devilfish

I noticed that at low RPM, around 1200-1400, the engine have some trouble running smooth. It doesnt matter if im going fast in high gear, or slow, crawling forward. But its more noticeable at low speed and low gears ( I can feel it better in the car ).
I can hear it on the exhaust note, tiny tiny popps/cough here and there and the car "bucks" slightly. Abow 2000 its mooth.
More timing did wounders, and now im pretty postive that someone else then me would not even notice it. But I do, its till there
I tried it "all" i think. Add even more timing,more fuel/less fuel. Keep it in closed loop, disabel DFCO etc etc. But I cant seem to tune this issue out.
And as I run a 6spd I got a "direct" link between the engine and the tiers, so I feel every tiny little "couch"/"jerk" the engine does. Im sure auto guys with the same combo wount feel this at all.

Can it be that I reach the "best i can do" point with the 730 ecm and my combo? perhaps next step is to change cam/inakte or even another type of EFI.
I start to think the issue is that lt1 intake wount work 100% with the 730 ECM.
perhaps its the "batch fire", or that I cant adjust for split BLMS like the lt1 guys can? And that shows its ugly face at low inj DC and low MAP/low RPM? Im fishing here...

Well, I just needed to ventilate.

Thanks for your time..

regads

DENN_SHAH

iTrader: (1)

ULTM8Z had some problems with a miss, im not sure if these will help you or not.

https://www.thirdgen.org/forums/diy-...-question.html

https://www.thirdgen.org/forums/diy-...ram-split.html

devilfish

Thanks for the links. I seen those before. And I dont think i have a missfire. I use the WB on the passenger side headers and the NB on teh driver side. And I got no mitchmatch between the cylinderbanks.

Thanks

Z69

You may not have adjusted the fuel/SA enough.
Also, a lot of the idle code uses a 15 mph qual.
You could have a DE tuning problem also.
There's a o2 Mv vs Map? table also. Not sure if it's in a public xdf.
(I've been playing with 6E lately so my brain keeps defaulting to g/s & LV8.)

devilfish

Thanks for the reply

The BLMs at the "probleme" RPM ( 1100-1400 ) is between 124-128, so the NB is happy, and I got no mysterious A/F spikes on the WB.
And I can feel it regardless of speed, they key is low rpm operations. But ofcrouse, its more noticeable at low speed and low gears. Where you more can "feel" it in the car.
Just like a small missfire here and there. You can crawl slow in first gear super smooth for 10,20, even 30-40 meters, then all of the sudden, a small surge. Then its smooth again. Its not much, not like you hit the head on the steeringwheel, but its there. Also I can hear in the exhaust note that its a "gargle" sound, like its getting to much/to litte fuel. And abow 2000rpm, super smooth, like a switch. I even tried to copy all of the ve +timing from the 1800-2000 area to 1100-1400, just to try. But no change.
What really helped whas to put in much timing, I whent from 34 degrees to 40 degrees, and this made a huge improvment.

I know im not "suppose" to drive it in those low rpms, but its annoys the hell out of me. And I driven lt1 car with the hotcam that got no probleme with low rpm driving. SO this leads me to hink its a fuel/air distribution probleme. And perhaps nothing I can do about. If I dont change ECM or intake.



What do you mean about DE tuning? If you mean de-accel fueling I tried to play with that to. But in the loggs I can se no evidence that de-accel is acivated during this.

o2 Mv vs Map? hmm, need to look for that.

best regards.

Z69

check out the 8d tuning section again. It's up there.
I've got 6E on the brain. 8D uses R/L in the description.
My thought is your setup has you running on the lean side and when the fuel is cycled by the ecm to get the o2 to cross count your going too lean for an instant at those rpm/airflow map values. Added timing making it run better is another indicator you may be lean in that area.
DE = Deceleration Enleanment. You could change the quals on it for one run to verify that is not the problem.

devilfish

I have disabel DE total. No change. I used open loop only, and tuned to a richer AF using my WB, still the same behaviour. I played with the IAC, and i have mange to get it better with the IAC, but I reached to the point where the IAC drives the car for you, not what i whant.

I will try some more things this weekend, then call it.
I will NOT run smooht under 1600rpm no matter what.

thanks

Z69

What cam?
What WB AFR?

Actually, what's the whole setup?

You may have a preconceived notion as to what is going on or is needed.
Or you may have adjusted something an amount that you thought was enough but it wasn't.
Some people take right to this stuff, others need to work at it, and still others never get it.
Understanding what the engine is telling you is the key. Whether it's the o2 mv or how the throttle response feels.
Sometimes it's just a bad combination of parts that needs to be crutched to work decent.

RednGold86Z

iTrader: (1)

But usually it's just a spark plug or wire arcing to a place it's not supposed to.

3.8TransAM

Might want to take a look at a few different bins and check out how they have the proportional gains set up for the 02 sensor :-)

I tend to make it the last place I go, but if fuel/timing, both up and down dont change anything and u have 100% verified no electrical/mechanical issues I would take a look.

later
Jeremy

devilfish

thanks guys for taking the time.
I will try to explain it from the beginning. Sorry if the English is not top notch.

My engine combo:

355
TRW forge pistons 9.87:1 comp
SCAT forge rods and crank
Converted LT1 intake from lt1intake.com
Full headers
3" exhaust.
LT4 hotcam
comcams R lifter
Canfield/Jegs 197cc heads 64cc
Stock TB.

Car is a 1991 corvette 6spd with 3:54 rear end.

The probleme I experience is at low rpm operation. This engine combo is far from radical. So what I whant must be achievebal ( i think ).
Under 1800/2000 rpm I experince that my engine is not running smooth. Over 2000rpm, supersmooth.
If I go in slow traffic and first gear, crawling, the car tend to jerk/buck/cough time to time. I can go smooth for some meters then ( without any change in TPS ) it bucks/jerks/cough, then smooth again. I guess you can call it like a "missfire", but not as severe. During this I can also hear on the exhaust note, that the engine does not like it. Its like the combustion is not "smooth", I can hear "gargel" from the exhaust from time to time ( i have a whery open exhaust system ).
I have ofcrouse doubel checked the mechanical parts. Plugs, wires, injectors, cap, fuel pressure etc etc.

Tuning has made much improvment. Add timing helped. But i reach the limit with timing, more is worse, less is worse.
Also IAC has helped.
BLMS at those areas is between 125-129. No A/F spikes on the zetronix WB.
I tried to richen up aswell as lean it out, no change. Also tried to run in open loop, but the behavoir is still the same.

I search ALOT about this. And it seems that more then me has the same probleme with low rpm+"preformance" cam + manual.
As the manual tranny makes a "direct link" between the engine and the tiers I can feel any "cough/jerking" the engine makes.
I know im under the cams "powerband" but, I must be abel to use the car in a good way in stop and go traffic or its just ridiculous.
I ride in a friends 92 lt1 vette with the hotcam ( stock heads/6spd ) and that car is so much smoother then mine.
And that make me suspect that perhaps the lt1intake and the hotcam dont "like" the 730 ecm, perhaps its the "batch fire" mode or the lack of individual injector fuel trim, i dunno.
One last note, if I go at a fast speed but low RPM ( under 1800rpm ), using high gear, 5th or 6th. I can hear ,from time to time the ,same kind of "unclean" burn sound in the exhaust. But as Im in higer gear I cant feel it the same amount as in first/second gear.
I also provide my latest .bin file.
Thanks..

devilfish

Fuel and timing is what I belvied whas the probleme. But when you change those 2 factors and nothing seems to cure it. You tend to get lost. And the tuning goes from a somewhat controlled session to a "desperate" trial and error madness.
----------
Even thou i replaced both plugs and wires i will do it again. I even took ridiculous measures to keep the wiers from "touching" any engine parts.

One thing I have not cheked yet is if I have any intermittent electrical issus at the injectors. Like a bad wire or something. Thats next.

Thanks

Jaysz28

iTrader: (30)

isn't that rpm 'area' about where the two spark tables overlap? If so, could a descrepancy might cause something like this


also double check the overlap in the ve table area

good luck with it.

-jason

devilfish

Yep, i go from closed TPS spar tabel to main tabel. But the transition is smooth.

thanks

Cflick

I wouldn't be surprised if the problem is there above 2000, but you just can't sense
it as it's smoothed out by the RPM.
Have you put a timing light on each cylinder ? Detect any cross-fire ?

devilfish

I have not put a timing light on each cylinder, just on no1 to set base timing.
Can you explain a bit more about "cross-fire" ? Im open to all suggestion. As I have not yet tuned this probleme out.
Thanks for your help

Devil..

Cflick

Basicly, leakage from one spark plug wire to another.
I've seen it on mine. Generally, a sign that the wires need replaced, or a dist. cap.
The effect seems most prominant at idle, and low RPM, when I've seen it.
A V8 fires every 90 degrees. I put a tape ( masking tape, 'cause I'm a cheap SOB ) and marked it for every ten degrees. Watched #1. Firing at whatever it fires at idle, perfect.
Moved the light to each wire. Two of them each showing two different numbers on the balancer.
Let's use #1 just as an example. Light shows, say 20 BTC. As you watch it,it shows
20..........20...........20...........20..290...20........20........20
Ah HA ! It's NOT supposed to fire at 290, ever. Not the #1 cylinder anyway.
Put the light on the cylinder that's supposed to fire at 290 and see..
290..........290...........290...20......290........290
Well, THAT cylinder should never fire at 20 !
Grab the wire that goes to that cylinder to move it. POW ! The wire moved me. Violently.
In my case, it was I think 4 and 7, whichever wires cross at the dist. cap. #1 looked good all the time. ( short wire that crosses nothing else )
Off to the wires store. Change the wires. Idle was instantly smoother. No noticable difference at 3000 RPM on the freeway.
The thing was "cross firing" the wrong cylinder sometimes.
Note that an inductive pick-up light fires on spark current, not voltage.
A random failure to flash indicates a miss on that cylinder. New plug time.

You say you have taken great pains to avoid wires crossing other things, so note that the light fires on current.
You can run an injector wire through the pickup, but only one of the conductors, not both, and the light should flash on injector firing.
The trick here, would be to look for a pattern that doesn't match the other injectors.
I don't know what you should see, but whatever it is, it should be the same as the others.
It won't tell you if there's a spray pattern problem, a stuck pintel, or anything like that, but if it shows an electrical weirdity on one injector......
Say the light fires reliably on both wires separately for each injector, except one.
I'd look hard at the one that's different.

The light might not fire at all on a single injector wire, in which case you can wrap the wire around the inductive pickup a few times, and it will. Of course, you do need enough slack in the wires to do that. Might not be practical for you.

Found a spray pattern problem with an injector on a TBI system that way, since the light
fires on THAT injector only, and only exactly when it sprays.

It's not what a timing light is meant for, but it's *my* light, so I can use it any way I want.
It's taught me a few things.
Just a few thoughts.

devilfish

Thanks for explaining. I will try what you posted m8

slowolej

It's really tough to give suggestions without driving the car. Provided that the electrical and mechanical components are ok, I've found that when light throttle surging isn't due to EGR or cam overlap issues, it seems to be excess timing more often than not. I know, that doesn't match up with what you've found. But it didn't sound like you had to increase VE when you increased timing, and generally adding 6 degrees advance would tend to cause the NB to show leaner readings. So I'm wondering if you had a little too much advance and too much fuel along with it.

If it is a problem with too much timing you might see it in your oil temperature if you have a way to monitor that parameter. You could also reset timing back to 34 degrees then try using the NB and INT as an indication of whether or not the VE needs to be reduced to match.

The other item I noticed is that there are large changes in timing around the rpm range where you're having troubles. Between 800 and 1400 rpm timing advances between 6 and 7 degrees. That's quite a change for just 600 rpm and that alone could cause surging Maybe you can try increasing timing some at the lower rpm, or try decreasing timing at the upper end of the table?

Just a few thoughts.

anesthes

iTrader: (12)

I don't believe that table actually works.

Or maybe I need to re-read the hack, but if i'm coasting at 0tps, and my closed tps table says 29 degrees, why do I see 40 degrees in the log? heh.

-- Joe

Cflick

More than once have I had to go back through the various write-ups, particularly RBob's very old write-ups on spark, and trace through step by step to understand why the log didn't agree with the light. In every case, I'd overlooked something, and got an offset wrong, usually in the ALDL stream definition file.

devilfish

Hi

First, thanks for the time you take to help me. I really appreciate it.

I made some progress the last days, I will try to sum it up for you.

Im now pretty sure that the jerking/bucking at low rpm is due to "unclean" combustion for some reason. I can hear it on the exhaust note, gurglin/poping sound. Not much, but its there.
And the jerking/buking almost always accur just before/after or during these moments of "pops/gurgel".

I tried to duplicate that condition at higher rpm ( 2500 and abow ) but faild to do so. From 2000-4000 to WOT the engine is spinning like a cat.

I reworked my timingtabel. This engine is WHERY sensitive to changes in the timing tabel at low RPM/MAP. I did a drastic change at the "troubel area" and reduced timing to 28-32. Almost a 8 degree drop, and that seemd to help drivability.
As a side note I can say that 38degrees is better then 34 but 30 is better then 38. So again, whery time consuming to tweak the timing on this engine. Cant seem to find trends..

BUT in the end I suspect that this only "mask" the condition more then help it...
( I can still hear it on the exhaust note ).

I made one interesting note.
I drove the car in bad weather for the first time with this engine combo. A little rain and the temp where around 57 degrees Fahrenheit ( it has been around 75-78 and suny on my other tuning sessions ).
I could tell the engine liked it. Much smoother. I can even say it where a 80% improvement.
I even tried to drive at ridiculous low rpm, just to check.
This is interesting, because this make me belive I can still cure it

More things I noted.
My INT is not whery stabel at low rpm. The BLM is stabel, around 126-128. But the INT is "pendling", from 118-134 and back again. Perhaps normal at low rpm?
My BLM at idle is never constant. Sometime its dead on 126-128. Sometimes its 134. BUT after searching on this site, I found its pretty "normal" to have a mixed results on tuning IDLE with a "preformance" cam.

Next is.
New spark wires.
New plugs
New coil

Then I will try to reduce the 02 "proportional gain" tabel. To calm the 02 down. Just have to patch in the gms/sec into datamaster.

Thanks

Cflick

Odd, but *I* would stay around 30 and sneak back up s-l-o-w-l-y.
In fact, I'd back off till performance definitly drops, then sneak up on it.

And, makes me believe you can too. It's a clue.
Much denser air, lower temp, high humidity.
Tends to suggest it's running rich. ( denser air at the same fuel is leaner ) but the BLM/INT should show that as well.

As long as the BLM is staying between limits, *I* would let that go for a bit.
It suggests fuel is within the range of the machine to respond and control it to final target.
Timing will affect the apparent fuel mix, so that's not going to settle as long as you're tweeking timing anyway.

A note on idle....
With the 7747 in my truck, same day, within an hour, same engine temp, same gas, same everything, I'll see idle BLM settle around 138-140. 1/2 hour later, it'll settle around 112-116.
Go figure !? A rather dramatic difference for essentially no-changes otherwise.
With the 8746 in the truck ( which uses an IAT sensor ) solid at 128.
Both of these allowing it to idle several minutes, like 20, so it's well past the 12 second BLM delay in the 8746 that's not in the 7747.
A clue, I know, but a clue of what ? Likely IAT, but I don't see how the intake air is THAT different, but the IAT is not in the ALDL ( replaced by spark advance ) so it could be.