Weird MAF table...
#1
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Weird MAF table...
See the attachment before reading on...
I did some datalogging with a wideband and Im seeing some funny results. It looks like there is a kink in the table for some reason. Its almost as if its two MAF curves superimposed over eachother. I dont think its anything on the computers side as it appears to be producing the correct output for a given input.
I suspected that there would be a point in the cars operating range where the flow through a big MAF would go from laminar to turbulent. It seems logical as, from the reynold's number, it should start off laminar and go turbulent at some point at higher flowrates. Anyone think this could be the possibility? Maybe the MAF is hosed? Its definatly the right direction as the car is wicked lean in that area with the stock LS1 MAF table. With that table, its fairly close for the most part. The intake track itself is basically a large cone air filter, MAF, and then the carb hat hooked up to the TBI. I dont know, maybe there really is such a thing as 'too big'.
I did some datalogging with a wideband and Im seeing some funny results. It looks like there is a kink in the table for some reason. Its almost as if its two MAF curves superimposed over eachother. I dont think its anything on the computers side as it appears to be producing the correct output for a given input.
I suspected that there would be a point in the cars operating range where the flow through a big MAF would go from laminar to turbulent. It seems logical as, from the reynold's number, it should start off laminar and go turbulent at some point at higher flowrates. Anyone think this could be the possibility? Maybe the MAF is hosed? Its definatly the right direction as the car is wicked lean in that area with the stock LS1 MAF table. With that table, its fairly close for the most part. The intake track itself is basically a large cone air filter, MAF, and then the carb hat hooked up to the TBI. I dont know, maybe there really is such a thing as 'too big'.
#2
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
See the attachment before reading on...
I did some datalogging with a wideband and Im seeing some funny results. It looks like there is a kink in the table for some reason. Its almost as if its two MAF curves superimposed over eachother. I dont think its anything on the computers side as it appears to be producing the correct output for a given input.
I suspected that there would be a point in the cars operating range where the flow through a big MAF would go from laminar to turbulent. It seems logical as, from the reynold's number, it should start off laminar and go turbulent at some point at higher flowrates. Anyone think this could be the possibility? Maybe the MAF is hosed? Its definatly the right direction as the car is wicked lean in that area with the stock LS1 MAF table. With that table, its fairly close for the most part. The intake track itself is basically a large cone air filter, MAF, and then the carb hat hooked up to the TBI. I dont know, maybe there really is such a thing as 'too big'.
I did some datalogging with a wideband and Im seeing some funny results. It looks like there is a kink in the table for some reason. Its almost as if its two MAF curves superimposed over eachother. I dont think its anything on the computers side as it appears to be producing the correct output for a given input.
I suspected that there would be a point in the cars operating range where the flow through a big MAF would go from laminar to turbulent. It seems logical as, from the reynold's number, it should start off laminar and go turbulent at some point at higher flowrates. Anyone think this could be the possibility? Maybe the MAF is hosed? Its definatly the right direction as the car is wicked lean in that area with the stock LS1 MAF table. With that table, its fairly close for the most part. The intake track itself is basically a large cone air filter, MAF, and then the carb hat hooked up to the TBI. I dont know, maybe there really is such a thing as 'too big'.
I am not seeing the same problem as you though.
This is what my MAF table looks like
It holds between 12.4 and 12.7 on the Wideband across the RPM band.
I think it is that large straight piece of pipe that you are using for an intake.
My intake setup has a couple of large sweeping turns too it.
#3
Supreme Member
iTrader: (1)
Join Date: Mar 2000
Location: Corona
Posts: 1,692
Likes: 0
Received 1 Like
on
1 Post
Car: 92 Form, 91 Z28, 89 GTA, 86 Z28
Engine: BP383 vortech, BP383, 5.7 TPI, LG4
Transmission: 4L60e, 700R4, 700R4..
Axle/Gears: 3.27, 2.73
This is TBI? Like standard 454 TB with big injectors? Or some other setup?
If it has something like dead-headed injectors, and a solid fuel system, I could imagine a harmonic resonance in the fuel system, but that would show a strong RPM correlation, not a MAF problem. Could add an accumulator (basically a fuel pressure regulator with the outlet blocked).
I'd try a longer straight intake pipe between MAF and air filter, and then try a longer pipe between MAF and hat, and see if either makes a difference.
If it has something like dead-headed injectors, and a solid fuel system, I could imagine a harmonic resonance in the fuel system, but that would show a strong RPM correlation, not a MAF problem. Could add an accumulator (basically a fuel pressure regulator with the outlet blocked).
I'd try a longer straight intake pipe between MAF and air filter, and then try a longer pipe between MAF and hat, and see if either makes a difference.
#4
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Dimented one other thing, you might be setting up a standing wave in that particular area. My suggestion is to put a 45 or 90* corner in the intake tract and see if this anomoly goes away.
#5
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
The weird thing is that I dont have any piping. The maf, cone element, and carb hat are all hooked to each other. If it was resonance, id expect to see it be more a function of RPM. Id also think fuel, but that would show with RPMs as well. This seems to be global and based on MAF flow more then anything else. I was also thinking of trying the old setup with piping, but I recall having standing wave issues with that. Seems like it needs to be more non-uniform like the later intake systems. Ill have to keep looking...
Last edited by dimented24x7; 12-12-2006 at 07:49 AM.
#6
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
I lied. Im still stumped...
Last edited by dimented24x7; 12-15-2006 at 08:35 PM.
#7
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
I did reconfigure the MAF ducting. It did help, and the car does go 0-60 in 5 seconds or so, but its still lean down low.
Trending Topics
#8
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
On a side note, what engine are you running now Dimented.
Is that the deep dished piston HD 20270 crate 350 TBI with Vortec heads and 204/214 "RV" cam combo that you have been running? If so, I might need to pull out my Vortecs, blend the bowls a little, port the exhaust, cut them for 2.02/1.60s and swap them on.
Last edited by Fast355; 12-15-2006 at 09:01 PM.
#9
Supreme Member
Join Date: Jun 2000
Location: In reality
Posts: 7,554
Likes: 0
Received 1 Like
on
1 Post
Car: An Ol Buick
Engine: Vsick
Transmission: Janis Tranny Yank Converter
Can you post a pic of the intake tract?.
Might be your MAF table is reflecting something *reversion* wise going on. The air flow has to match what the engine's *demand* is. ie If the engine has some point where the mechanical VE goes high or takes a dip, the fuel *demand* will make the same change.
Might be your MAF table is reflecting something *reversion* wise going on. The air flow has to match what the engine's *demand* is. ie If the engine has some point where the mechanical VE goes high or takes a dip, the fuel *demand* will make the same change.
#10
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
I think I figured it out. After some more tuning, I got a standard MAF table with no kinks in it. Like you implied, the problem only happens below 1800 RPM. I think the issue is backflow from cylinder pulses in the intake. Easy way to fix it is not to operate the engine at low RPMs/high load, or run a baffle style MAF. Nothings perfect, I guess. Thats probably why GM has the dynamic fueling.
Fast, its a 350 w/ vortec heads, edelbrock intake and performer plus 'RV' cam. Has 8.7:1 or so CR. I finally got the timing fully dialed in (needs LOTS of it), and it is SICK. Doesnt pull real high, but has cummins turbo diesel like torque through 3600 RPM. Have you done any wideband datalogs? How about the timing? From tonight, the MAF is very sensitive to the intake configuration. Incidetally, at WOT, SD works fine with TBI as theres not much fuel dynamics at high MAPs. Its only at part throttle that I had all the problems.
Fast, its a 350 w/ vortec heads, edelbrock intake and performer plus 'RV' cam. Has 8.7:1 or so CR. I finally got the timing fully dialed in (needs LOTS of it), and it is SICK. Doesnt pull real high, but has cummins turbo diesel like torque through 3600 RPM. Have you done any wideband datalogs? How about the timing? From tonight, the MAF is very sensitive to the intake configuration. Incidetally, at WOT, SD works fine with TBI as theres not much fuel dynamics at high MAPs. Its only at part throttle that I had all the problems.
Last edited by dimented24x7; 12-16-2006 at 12:57 PM.
#11
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Ive seen that companies make probe MAFs specifically designed to handle reversion. Ill have to try one one of these days.
#12
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Its definatly a reversion issue. Once the throttle passes a certain point, it bogs down at low RPMs. Let out a little bit and the AFRs immediatly come right back up. Its not a huge issue, but a little annoying with a stick. With the auto, it was never an issue as it was impossible to go below 1500 RPMs.
#13
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Yeah, its similar with mine. Goes lean at very low RPMs and high throttle. Other then that, it runs well. Guess Ill have to take the good with the bad...
#16
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
If I had MPFI or TPI I would... I have a CAI and its bad enough having the AE be a moving target. The MAF is also nice because its easy to tune.
Fast, have you looked at the timing in that area? Might also be a good idea to verify it with a WB before coming to a conclusion, if you havnt already. It could also be that the lower flows in the MAF table are off. My table needed alot of tweaking as the actual flow and the reported differed alot.
Fast, have you looked at the timing in that area? Might also be a good idea to verify it with a WB before coming to a conclusion, if you havnt already. It could also be that the lower flows in the MAF table are off. My table needed alot of tweaking as the actual flow and the reported differed alot.
#17
Supreme Member
Join Date: Jun 2000
Location: In reality
Posts: 7,554
Likes: 0
Received 1 Like
on
1 Post
Car: An Ol Buick
Engine: Vsick
Transmission: Janis Tranny Yank Converter
Hmm, easy to tune, and here you are having reversion/ tuning issues.... <G>
#18
Supreme Member
Join Date: Jun 2000
Location: In reality
Posts: 7,554
Likes: 0
Received 1 Like
on
1 Post
Car: An Ol Buick
Engine: Vsick
Transmission: Janis Tranny Yank Converter
So far thou, I haven't seen a combo., that didn't run it's best on MAP. With MAF your always, always having to fight the misreporting error of manifold filling. Well, as far as with a hi-po combination, goes. The transistional AE will always be something you have to chase around with a MAF. Long small runners, and a small plenum are all crutches to not needing much AE, interestingly enough that discribes TP to a *T*. But, even with those items, GM still went to MAP in the later TP's.
#19
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
As for the tuning, its one small area that normally would never be realized with an automatic. With 2.77's and a TKO, its real easy to duck into low RPMs, and even easier to dump down below 600 RPM where the timing is reduced to prevent the engine from kicking the starter clear off the block. Other then that, its quite drivable, and runs as well as an old **** heap can be expected to. 0-60 in 5 seconds with good low end torque aint bad for an old junker
We could go on and re-ignite the whole MAF vs. SD arguments, but in some apps, one system will work better while some apps the other will work better. Despite the whole low end bog at max throttle, I definatly prefer MAF with the TBI setup. It decouples the fueling from the engine and the fuel dynamics. If I had MPFI, Id probably run SD. The MAF has very good resolution, and is more versital then SD, but lacks the dynamic range. Conversly, with SD, the fueling and engine are closely coupled. Neither sysem is perfect... Such is life.
Last edited by dimented24x7; 12-17-2006 at 08:39 PM.
#20
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
You're right, nothing will cure a bad combination.
So far thou, I haven't seen a combo., that didn't run it's best on MAP. With MAF your always, always having to fight the misreporting error of manifold filling. Well, as far as with a hi-po combination, goes. The transistional AE will always be something you have to chase around with a MAF. Long small runners, and a small plenum are all crutches to not needing much AE, interestingly enough that discribes TP to a *T*. But, even with those items, GM still went to MAP in the later TP's.
So far thou, I haven't seen a combo., that didn't run it's best on MAP. With MAF your always, always having to fight the misreporting error of manifold filling. Well, as far as with a hi-po combination, goes. The transistional AE will always be something you have to chase around with a MAF. Long small runners, and a small plenum are all crutches to not needing much AE, interestingly enough that discribes TP to a *T*. But, even with those items, GM still went to MAP in the later TP's.
To some extent, the AE is also there to cover up delays as well as enrich the acceleration. One issue Ive had with both MAF and MAP is the need for a short pulse of AE to cover for lag in the system. The AFRs will go dead lean for a split second without some form of a short, quick pulse to cover the transition.
#21
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
I took another look at the datalogs from this. It doesnt look like an issue with the MAF at all. The MAF is reporting around 100-120 gms/sec at 1800-2200 RPM. This equates to VEs of around 95%. The PWs too are in line with the airflow. The PCM and MAF are doing what theyre supposed to be doing, but still the AFRs where dipping down to 20:1 at WOT until the RPMs come up a bit. Also not giving full throttle to the motor will bypass the issue to a good extent. It will also not happen at higher RPMs. the lower the RPM, the worse it is.
It could be a fuel issue, but the pressure is steady at 18 PSI, so the pump is ok.
Could this instead be some cam timing issue, or maybe the fuel pulses being scavanged out of the cylinder by the cam overlap? something wacky with the injectors? This is definatly one wierd and very strange problem. Even at full injector duty cycle at low RPMs it still leans out a little. When it does have fuel, it goes like hell. It also has a slightly lopey idle, which is strange for a cam with only 204 degrees of intake duration. In addition, it sounds like theres ball bearings bouncing around in my y-pipe when the engines under load. Sounds like fuel burning off in the exhaust.
It could be a fuel issue, but the pressure is steady at 18 PSI, so the pump is ok.
Could this instead be some cam timing issue, or maybe the fuel pulses being scavanged out of the cylinder by the cam overlap? something wacky with the injectors? This is definatly one wierd and very strange problem. Even at full injector duty cycle at low RPMs it still leans out a little. When it does have fuel, it goes like hell. It also has a slightly lopey idle, which is strange for a cam with only 204 degrees of intake duration. In addition, it sounds like theres ball bearings bouncing around in my y-pipe when the engines under load. Sounds like fuel burning off in the exhaust.
#22
TGO Supporter
Join Date: Aug 2001
Location: NJ/PA
Posts: 1,008
Likes: 0
Received 0 Likes
on
0 Posts
Car: Yes
Engine: Many
Transmission: Quite a few
Sounds an awful lot like where the cam starts it's effective range. You start scavenging more effectively, and the engine VE is going to be high. You might be stripping the fuel off of the intake walls, and causing a momentary lean spot. Could be that on the throttle transition, you need to kick out some extra fuel.
#23
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Aye, captain, shes giving us everything shes got...
Ive gotten to the point where Im at 100%+ DC with the added MAP and TPS AE during transition. Fast355 reports his engine is pig rich with these settings during AE, so its definatly me. In third or fourth with sudden WOT, it starts off dead lean and gradually gets richer and richer until it comes up to the desired AFR at 3000 RPM. The MAF and PW readings look good. Sometimes its ok, but alot of times it just goes dead lean and doesn make much power. My theory is that maybe the fuel pulse is being sucked clear out into the exhaust.
Ive gotten to the point where Im at 100%+ DC with the added MAP and TPS AE during transition. Fast355 reports his engine is pig rich with these settings during AE, so its definatly me. In third or fourth with sudden WOT, it starts off dead lean and gradually gets richer and richer until it comes up to the desired AFR at 3000 RPM. The MAF and PW readings look good. Sometimes its ok, but alot of times it just goes dead lean and doesn make much power. My theory is that maybe the fuel pulse is being sucked clear out into the exhaust.
#24
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
I wonder if slewing the injector firing timing would help? Maybe delay the firings enough to give the exhaust valves time to seat on the cylinders that will be on their intake cycles.
#25
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Dimented,
How much fuel are you running on your combination?
I have been tuning Kurt's (OldRed95 on FSC) 1995 C1500s TBI 350 and have found that I had to peak out his VE table around 2,000-2,800 rpm, despite running 61 lb/hr injectors at 25 PSI. His engine is basically the same as yours. The more fuel we keep giving it, the more it responds with that fuel.
How much fuel are you running on your combination?
I have been tuning Kurt's (OldRed95 on FSC) 1995 C1500s TBI 350 and have found that I had to peak out his VE table around 2,000-2,800 rpm, despite running 61 lb/hr injectors at 25 PSI. His engine is basically the same as yours. The more fuel we keep giving it, the more it responds with that fuel.
#26
Supreme Member
dim,
You think your experience is analogous to what I have been discussing in this thread?
https://www.thirdgen.org/forums/diy-...n-pattern.html
You think your experience is analogous to what I have been discussing in this thread?
https://www.thirdgen.org/forums/diy-...n-pattern.html
#27
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
It could be, but this seems to be a high MAP problem on my car. At low kPa's, its fine. At higher kPa's is when it starts to lean out and make that annoying bouncing ball bearings sound in the y-pipe.
It definatly responds to more fuel, but the calculated VEs are around 150%, which doesnt make much sense. Once the RPMs build, the AFRs come back in line. Due to the fact that it can fuel it even at increasing PWs and speeds leads me to believe around 160 PPH should be enough to feed it down low, unless there is something really FUBAR. I donno...
My best guess is that the exhaust pulses are vacuuming out the manifold at higher vacuum and low RPMs. Its really bad at around 400-600 RPM. Starts reading in % oxygen on the wideband. It was also an issue with the old ECM and ignition system. Its a damn strange problem. Ill have to keep looking, maybe theres some more logical reason for it.
It definatly responds to more fuel, but the calculated VEs are around 150%, which doesnt make much sense. Once the RPMs build, the AFRs come back in line. Due to the fact that it can fuel it even at increasing PWs and speeds leads me to believe around 160 PPH should be enough to feed it down low, unless there is something really FUBAR. I donno...
My best guess is that the exhaust pulses are vacuuming out the manifold at higher vacuum and low RPMs. Its really bad at around 400-600 RPM. Starts reading in % oxygen on the wideband. It was also an issue with the old ECM and ignition system. Its a damn strange problem. Ill have to keep looking, maybe theres some more logical reason for it.
#28
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
It could be, but this seems to be a high MAP problem on my car. At low kPa's, its fine. At higher kPa's is when it starts to lean out and make that annoying bouncing ball bearings sound in the y-pipe.
It definatly responds to more fuel, but the calculated VEs are around 150%, which doesnt make much sense. Once the RPMs build, the AFRs come back in line. Due to the fact that it can fuel it even at increasing PWs and speeds leads me to believe around 160 PPH should be enough to feed it down low, unless there is something really FUBAR. I donno...
My best guess is that the exhaust pulses are vacuuming out the manifold at higher vacuum and low RPMs. Its really bad at around 400-600 RPM. Starts reading in % oxygen on the wideband. It was also an issue with the old ECM and ignition system. Its a damn strange problem. Ill have to keep looking, maybe theres some more logical reason for it.
It definatly responds to more fuel, but the calculated VEs are around 150%, which doesnt make much sense. Once the RPMs build, the AFRs come back in line. Due to the fact that it can fuel it even at increasing PWs and speeds leads me to believe around 160 PPH should be enough to feed it down low, unless there is something really FUBAR. I donno...
My best guess is that the exhaust pulses are vacuuming out the manifold at higher vacuum and low RPMs. Its really bad at around 400-600 RPM. Starts reading in % oxygen on the wideband. It was also an issue with the old ECM and ignition system. Its a damn strange problem. Ill have to keep looking, maybe theres some more logical reason for it.
I had to ditch the cone style filter on mine. Put in an Astro style air box with matching filter. The cone filter was disrupting the MAF sensor readings.
I honestly still have not touched the stock 5.3 MAF tables, except to put 5 gms/sec in the lowest cell.
#29
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Just remembered this... Know what else is interesting, they force async fire at 80 Hz above 1300 RPM and around 55 kPa in these PCMs. Basically Im in async whenever Im at higher loads. I wonder if that is the issue? It seems plausable as the large, sudden intake pulses could be left high and dry with the injectors dribbling out fuel at 80 Hz rather then delivering it all in one shot in sync fire. With my luck itll agrivate the problem more being full sync, but if it cures the lean issue, Im going to drop a nuke on its *** and blow the manditory async code out of my bin. Im praying for thick clouds of black smoke out the tail pipe next time I hit the gas.
#30
Supreme Member
Just remembered this... Know what else is interesting, they force async fire at 80 Hz above 1300 RPM and around 55 kPa in these PCMs. Basically Im in async whenever Im at higher loads. I wonder if that is the issue? It seems plausable as the large, sudden intake pulses could be left high and dry with the injectors dribbling out fuel at 80 Hz rather then delivering it all in one shot in sync fire. With my luck itll agrivate the problem more being full sync, but if it cures the lean issue, Im going to drop a nuke on its *** and blow the manditory async code out of my bin. Im praying for thick clouds of black smoke out the tail pipe next time I hit the gas.
Interesting that you bring up asynch fueling. I have asynch disabled in my bin.
#31
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Just remembered this... Know what else is interesting, they force async fire at 80 Hz above 1300 RPM and around 55 kPa in these PCMs. Basically Im in async whenever Im at higher loads. I wonder if that is the issue? It seems plausable as the large, sudden intake pulses could be left high and dry with the injectors dribbling out fuel at 80 Hz rather then delivering it all in one shot in sync fire. With my luck itll agrivate the problem more being full sync, but if it cures the lean issue, Im going to drop a nuke on its *** and blow the manditory async code out of my bin. Im praying for thick clouds of black smoke out the tail pipe next time I hit the gas.
#32
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
The RPM thresholds dont actually do anything as the MAP thresholds are checked FIRST. If these are met, the PCM enters async. Ive had the same issue, a strange, high frequency shudder at high RPMs. Hopefully deleting the code will kill two birds with one stone.
#33
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
I am going to bump the MAP up as high as it will go and do the same with the RPM. Will let you know how it goes. At WOT, it definately waits until 4,000 rpm to enter asynch though.
#34
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Oops... I stand corrected. Went back and checked and the RPM threshold will disable it.
#35
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Man, got my hopes up too that I might have found the problem, lol...
I dont know, then. Maybe async is the answer. It does seem to be ok and starts recovering once its gotten up past 1500 RPM. Ill have to tinker with it and see if it makes any difference.
I dont know, then. Maybe async is the answer. It does seem to be ok and starts recovering once its gotten up past 1500 RPM. Ill have to tinker with it and see if it makes any difference.
#36
Moderator
iTrader: (1)
Join Date: Mar 2002
Location: Chasing Electrons
Posts: 18,432
Likes: 0
Received 227 Likes
on
212 Posts
Car: check
Engine: check
Transmission: check
I've found that to run async for the main fueling that the injector duty cycle has to be high. Greater then 90% is best. Otherwise it just doen't run right. I figured it had to do with fuel distribution. Some cylinders will be lean with others rich. All depends upon when the injectors fire and which cylinders are inhaling at the time.
RBob.
RBob.
#37
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Ive found that out as well. At lower DCs, the engine acts odd at higher loads and speeds.
Whats driving me crazy, though, is that at low speed/high loads its going really lean for no real reason at all. The fuel should be getting in there. At part throttle its fine, but once the loads build, it leans way out at low speed. I wonder if delivering the fuel as shorter pulses at a high frequency would help when its under low RPM, high load?
Whats driving me crazy, though, is that at low speed/high loads its going really lean for no real reason at all. The fuel should be getting in there. At part throttle its fine, but once the loads build, it leans way out at low speed. I wonder if delivering the fuel as shorter pulses at a high frequency would help when its under low RPM, high load?
#38
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Ive found that out as well. At lower DCs, the engine acts odd at higher loads and speeds.
Whats driving me crazy, though, is that at low speed/high loads its going really lean for no real reason at all. The fuel should be getting in there. At part throttle its fine, but once the loads build, it leans way out at low speed. I wonder if delivering the fuel as shorter pulses at a high frequency would help when its under low RPM, high load?
Whats driving me crazy, though, is that at low speed/high loads its going really lean for no real reason at all. The fuel should be getting in there. At part throttle its fine, but once the loads build, it leans way out at low speed. I wonder if delivering the fuel as shorter pulses at a high frequency would help when its under low RPM, high load?
I turned the asynch off and redyno'd in hotter conditions. On a 15* hotter day with the clutch fan engaged, it lost 10 ft/lbs of torque, but held the same peak HP. It felt much stronger at high RPM when the fan was disengaged.
#39
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Thats exactly what mine does at high RPMs. The cylinder intake cycles are much faster then the injector firings at high RPMs in async and it gets a strange high frequency vibration from it. Probably the rich, lean, leaner, rich, lean, leaner... as the injector firings are out of sync with the intake cycles. Im going to disable it and see how it works then.
Im also wondering whether or not this is still an AE issue down low. How much fuel does an accelerator pump deliver over time in a carb? Im going to max everything out as a last ditch effort and see what happens.
Im also wondering whether or not this is still an AE issue down low. How much fuel does an accelerator pump deliver over time in a carb? Im going to max everything out as a last ditch effort and see what happens.
Last edited by dimented24x7; 01-23-2007 at 12:00 PM.
#40
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Thats exactly what mine does at high RPMs. The cylinder intake cycles are much faster then the injector firings at high RPMs in async and it gets a strange high frequency vibration from it. Probably the rich, lean, leaner, rich, lean, leaner... as the injector firings are out of sync with the intake cycles. Im going to disable it and see how it works then.
Im also wondering whether or not this is still an AE issue down low. How much fuel does an accelerator pump deliver over time in a carb? Im going to max everything out as a last ditch effort and see what happens.
Im also wondering whether or not this is still an AE issue down low. How much fuel does an accelerator pump deliver over time in a carb? Im going to max everything out as a last ditch effort and see what happens.
Holley uses 30 and 50 cc accelerator pumps.
#41
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
30-50 CCs is around 20-35 grams of fuel. Wonder how fast its delivered? Over 2-3 seconds? Thats actually a decent chunk of fuel.
----------
Ive thought of enriching down lower, but Id like to actually get it to target the correct AFR. It seems the MAF is reporting a reasonable ammount of flow for the load and engine speed, so it should be in the ball park AFR wise.
----------
Ive thought of enriching down lower, but Id like to actually get it to target the correct AFR. It seems the MAF is reporting a reasonable ammount of flow for the load and engine speed, so it should be in the ball park AFR wise.
Last edited by dimented24x7; 01-23-2007 at 02:17 PM. Reason: Automerged Doublepost
#42
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Im definatly thinking this is an AE issue. It seems like this manifold needs LOTS and LOTS of fuel during transition. Added alot more and it definatly helps. Now, though, the AFRs are pegged at full rich when the throttle closes after AE. Its really bad after cruising on the highway. Hit the gas and booooggggg. Ive felt the manifold and it gets really cold while driving the car. Im probably going to have to put an RTD right in the manifold wall so I can actually see what temperature it is. Right now the AE is all over the place when its based off of the cool temp as the manifold is at whatever temp if feels like being.
#43
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Think I figured out the other half of the problem. I didnt have any filtering set for the MAF at high loads, so the computer seemed to be fueling per the instantanious airflow, which is near zero when there arnt any intake cycles. No intake cycle when the MAF is read, no fuel... Set the filtering so Id get more of an integrated signal, and it seems to work much better. No bogging down low and it tolerates lugging the motor. This car likes to get my hopes up, so Ill wait and see how it works when I try it again with a little less AE.
Last edited by dimented24x7; 01-24-2007 at 11:24 PM.
#44
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Think I figured out the other half of the problem. I didnt have any filtering set for the MAF at high loads, so the computer seemed to be fueling per the instantanious airflow, which is near zero when there arnt any intake cycles. No intake cycle when the MAF is read, no fuel... Set the filtering so Id get more of an integrated signal, and it seems to work much better. No bogging down low and it tolerates lugging the motor. This car likes to get my hopes up, so Ill wait and see how it works when I try it again with a little less AE.
Last edited by Fast355; 01-24-2007 at 11:35 PM.
#45
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
I think it was a big mistake on my part to underestimate the speed of the sensor. In reality, its probably faster then greased lightning. It makes sense as the lower the RPMs, the more discrete the signal is, so the fueling would crater if the sensor reads and intake pulses where out of phase with eachother. Another strange problem... Im surprised it ocured to me in the first place to check it.
In the later MAFs, they may have put something in to integrate the signal internally. If its blowing black smoke and is rich on the wideband, then I wouldnt sweat it.
This is what I was using and it seems to help alot. Potentially itll never be perfect, though, as there will always be some aliasing in the signal at low RPMs.
In the later MAFs, they may have put something in to integrate the signal internally. If its blowing black smoke and is rich on the wideband, then I wouldnt sweat it.
This is what I was using and it seems to help alot. Potentially itll never be perfect, though, as there will always be some aliasing in the signal at low RPMs.
#46
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Works ok now with the filtering to integrate the signal. Acts the same way it did when I put it back in speed density last night. Momentary stumble at low RPMs and then it goes fine. No stumble at all when warm, so it must be too much AE when cold. About time...
#47
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Did some real time high speed datalogs and the MAF output is a very dirty signal at WOT. Alot of it is from the engine intaking air, but a good chunk is also from the resolution limits of the hardware. Without the filtering, the PCM was tracking along the signal. Slide filtering helps alot and the car doesnt go dead lean for a long time like it did before. Leans a little, but recovers and goes just fine. Think adding a moving average filter would help on the frequency side?
The first graph is a 300 msec snap shot of the frequency output at higher RPMs. The second is another 300 msec snapshot of taking off in second gear from a dead stop.
The first graph is a 300 msec snap shot of the frequency output at higher RPMs. The second is another 300 msec snapshot of taking off in second gear from a dead stop.
Last edited by dimented24x7; 01-27-2007 at 06:30 PM.
#48
Where are you picking off the data? Is that data taken directly off the MAF sensor itself through a F/V converter? What hardware are you saying lacks the resolution, the PCM or your logging hardware? A lack of resolution acts as a filter in and of itself. From the looks of the datalog and then looking at a MAF table from an LS1, you are varying about 200 Hz at 7.6 kHz. That is about an 8.8 gm/sec swing at 108 gm/sec. Right at 8%, a whole lot. A moving average filter will definetly help but I think the 20 point filter in the graph is too much. JMHO
#49
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,121
Received 428 Likes
on
368 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Where are you picking off the data? Is that data taken directly off the MAF sensor itself through a F/V converter? What hardware are you saying lacks the resolution, the PCM or your logging hardware? A lack of resolution acts as a filter in and of itself. From the looks of the datalog and then looking at a MAF table from an LS1, you are varying about 200 Hz at 7.6 kHz. That is about an 8.8 gm/sec swing at 108 gm/sec. Right at 8%, a whole lot. A moving average filter will definetly help but I think the 20 point filter in the graph is too much. JMHO
The setup has the frequency straight from the MAF going into the speed sensor circuitry in the ECM. Straight shot, NO converters of any kind.
I am running the stock 85mm MAF sensor on mine from a LS1/5.3 Vortec. I am running the stock MAF table from the newer LS1. Sits right at 125-131 BLM at all times, except at idle with the A/C on where it creeps up around 140 BLM.
Still don't fully understand his problem with the setup.
I think Dimented is talking about the rate at which the MAF signal is read by the code as well as possibly the datalogging equipment.
On the other hand, I have Monday off and am going to have to change yet another U-joint. HORRIBLE vibration again while accelerating around 2,500-3,500 rpm at part throttle. Checked and its the rear U-joint AGAIN. Crappy Taiwan U-joint. Anyone know of a good old quality AMERICAN piece to replace it with. Its taken a horrible beating lately.
Last edited by Fast355; 01-27-2007 at 09:56 PM.
#50
Supreme Member
Thread Starter
iTrader: (2)
Join Date: Jan 2002
Location: Moorestown, NJ
Posts: 9,962
Likes: 0
Received 3 Likes
on
3 Posts
Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Where are you picking off the data? Is that data taken directly off the MAF sensor itself through a F/V converter? What hardware are you saying lacks the resolution, the PCM or your logging hardware? A lack of resolution acts as a filter in and of itself. From the looks of the datalog and then looking at a MAF table from an LS1, you are varying about 200 Hz at 7.6 kHz. That is about an 8.8 gm/sec swing at 108 gm/sec. Right at 8%, a whole lot. A moving average filter will definetly help but I think the 20 point filter in the graph is too much. JMHO
Fast, it shouldnt be, and never was, an issue with an auto as youll never actually get to low RPM, high load operation. At low RPMs, the instantanious airflow varies by +/- 20%. This causes the motor to run real erratic. When Im going around a corner in 2nd, without the filtering, the engine would plain crap out when I got back on the gas. Works ok with the filtering, but still goes somewhat lean at 800 RPM or so. Even that is more then tolerable, but Id like to see if using a rolling average filter on the frequency can help smooth things out even more. Ill have to tinker with it in excel and see what looks good. GM has one in these PCMs for filtering the derivative of the TIS input. That uses a full 50 samples as well as a convoluted method for weighting the start and end values in the sample set. Im going to take that over for the MAF and tweak it a bit. Maybe have the # of samples used be variable based on RPMs.
Last edited by dimented24x7; 01-27-2007 at 10:37 PM.