Cflick

Almost.
When the throttle is opened, air density in the manifold increases, causing fuel to condense out and wet the manifold. The important thing is that *that* fuel is not reaching the cylinders ! AE is to compensate and so keep a consistent AFR in the cylinders.

When the throttle is closed, the air density in the manifold drops considerable, the fuel hanging on the manifold walls flashes to vapor, so the mixture in the cylinders is considerably richer. DE compensates by taking fuel out of the air before the fuel evaporating off the manifold can excessively richen the mix in the cylinders. ( in theory. You still get a spike )

In a word, yes, but mostly to add fuel and richen the mix, since gasoline produces max power somewhat richer than stoich. This is *not* the purpose of AE ! After the initial burst of power, more fuel to cool cylinder parts.

Cflick

In my early days of experimenting, ( long before you and I met ) I had at one point the dist advanced ( do not try this at home, use only under adult supervision, batteries not included ) about 70 degrees. ( I forget why )
Can you say "hard start" ? I thought you could, but once it did fire ( in a forward direction ) the timing returned to right where it was programmed, so I gotta wonder about which reference pulse is used for what when ? It would appear that there is considerably more range than one might think.

morgsie

iTrader: (1)

Glad it worked for you. Like rbob said though, make sure the "SA - Initial SA" in your calibration matches whatever you see on the balancer. Changing your initial advance should have no affect on idle quality. The ECU should be controlling the timing once the engine is running.

dabomb6608

iTrader: (3)

[quote=Cflick;5554966]Almost.
When the throttle is opened, air density in the manifold increases, causing fuel to condense out and wet the manifold. The important thing is that *that* fuel is not reaching the cylinders ! AE is to compensate and so keep a consistent AFR in the cylinders.


How would this be compensated for in the dry manifolds found with port fuel injection? I am chasing a AE problem(so I think). If i barely touch the throttle or blip it when at temp the car is hesitant and drops in rpms right before it raises. The AFR goes rich to as shown on my WB. Is this too much AE in the low rpm areas?

mhelander

That might well be the case. As I installed XE262H, don't remember anymore did I dial it straight or advanced. Could be one reason for mismatch between distributor advance and zero initial SA.

Absolutely. Engine was starting exceptionally easy and fast when dialed to estimated 14*. I calculated that angle so that measured diameter of distributor base where factory mark is for 0*, multiplied by Pi, used result for dividing measured distance from intake 0* mark and multiplied by 180.

Used same 14* in calibration.

Now I've calculated new distance for 10* and used that as initial SA. Cranking takes little longer, like 1-4 seconds, but starts reliably.

That could be the reason. As it could also be affected by still little too rich choke AFR, pushing my luck with Champion plugs with some mileage and possible difference in distributor and initial SA degrees. Now tune seems to be working better so reading plugs for next heat range will be easier and more constant.

Anyways idle is now with IAT #0 about 700-750, throttle response is almost as good as in 14* and this thing really moves and is way nicer to drive in urban area.

Edit: forget to state that MPG (or km per liter) value jumped about 10-20 %. Best I got before was 4-6 when driving with very light throttle in even road & speed. Now I get 5-8 in urban driving. That's E85 so not bad at all as 5 is 20 liters per 100 km which was about same it was consuming 95E gas with stock cam before.

RBob

iTrader: (1)

[QUOTE=dabomb6608;5555247]There is a lot less runner area to compensate for, so the required AE is also a lot less. On dry intakes (MPFI) getting AE is tricky as it is so easy to go with too much or too little. A wet manifold (TBI) has a large amount of capacitance to absorb the changes.

Back to port injection, reduce the AE to the point that the INT starts to increase to compensate. That typically provides the best compromise. Many times the MAP based AE can be nearly eliminated.

RBob.

Doober

So, you're saying that if everything checks out, it would be possible to run the SFI-6 ECM with the 3400?

dabomb6608

iTrader: (3)

[quote=RBob;5555386]If your running in open loop would you need to just watch the wide band and see how much it goes rich or lean when AE is activated? I realize there is a little lag in what the wb reads but is doable correct?

I have reduced my AE rpm %multi tables in the lower rpm areas but havent got a chance to test it yet. I will also lower the CTS % multi table to get a overall reduction in AE.

RBob

iTrader: (1)

Yes, as far as I know, just needs a cam sensor for sequential injection sequencing. Can run either a distributor or a DIS set up.

I take it the 3400 is the same as the 3.4l f-body engine, that it has a seven notch wheel machined into the crank?

RBob.

RBob

iTrader: (1)

Yes, check the WB reported AFR for AE.

I'm not sure I'd use the CTS % multi table for across the board changes. I would use it to make changes based on engine coolant temperature.

For across the board change I typically use the AE PW tables. Reducing the whole table by say, 10%.

RBob.

1991sleeper

iTrader: (-3)

HELP ASAP PLEASE !! I'm at lowes and my car will not crank or turn over or nothin .. The security light is on and it has never been on before .. How do I disable VATs with ebl ? My GF is bringin my laptop .. I thought it was already disabled in the base bins ? I was varying my keys in my hand with a bunch of bolts n stuff idk I guess it
Killed the chip in the key ? Thanks

RBob

iTrader: (1)

VATs in the ECM only stops the injectors from firing. And yes, the supplied calibrations have it disabled.

You need to bypass the starter enable relay. Which is controlled by the VATs module, not the ECM.

RBob.

1991sleeper

iTrader: (-3)

Ok thanks .. I finally got it to start yesterday .. I've never seen that security light on before .. Idk what happened or how I fixed it .. I fisconnected battery n waited n hooked back up n that did nothing so I just sat there about ten min and tried again and it fired right up .. If It does it again ill bypass it .. How is this done ? Where is this module ?

RBob

iTrader: (1)

Likely the key is dirty or the ignition tumbler contacts are worn or dirty. After 5 minutes or so of key-off the VATs module allows a retry. No need to access the module, the starter interrupt relay is in the drivers side kick panel. Lots of posts on here on how to bypass it.

RBob.

Cflick

Remember which is ( primarily) for what.

AE and DE are compensations for manifold wetting.
PE is to deliberately enrich the AFR while the engine is under high load.

If you had direct into cylinder injection, then you would zero out both AE and DE, and not use them at all. You would then tune PE for what the engine needs under high load.

With port injection, you're somewhere between, and that makes it more critical and more difficult to "get right."
If you disable PE, ( only under adult supervision. You can roast expensive parts quickly ) then when AE and DE is right, you'll see *no* change in AFR opening or closing the throttle. You can safely do this in the garage with the engine under no load at all, but with no load things happen *very* quickly, so you're looking to minimize AE and DE spikes at best.
It'll get you in the ball-park within a few percent of where the engine wants it.

For me, I raised the point at which PE came in quite a lot, something like 80% throttle, and did my best to stay below that for tweeking AE and DE. When I was happy ( as opposed to making it perfect ) reset PE to more reasonable numbers, and then tune that alone.

88gunmetalgta

iTrader: (1)

I just found out I had a wire pinned wrong on my P4. Sensor grounds for IAT TPS and CTS were wired to the P4's pin B6 instead of B5 where they belong. I recently started having problems with the engine basically just cutting out randomly during cruise (indicating a ground issue, I thought) SES light would flicker, and on the WUD I'd see TPS% of 0, and CTS and IAT trouble codes would flicker. I figured I had a bad wire somewhere but it turns out I was on the wrong pin on the ECM connector.

Why did it run fine that way all last year? and why is it acting up now? Just curious, and want to get some input on whether or not I've got the problem solved. What's on pin b6 anyway? its unused by the P4

RBob

iTrader: (1)

B5 and B6 are both grounds in the ECM. Check that the EFI harness block grounds are OK.

RBob.

Napster134

Hello all,

I'm back and started tuning my supercharger for the summer. I've done a bit of cooling system work (3 core aluminum radiator, trans oil cooler, stewart al. water pump) but I think I'm going to need some fans to keep everything cool as the engine stays cool as long as I'm moving and the overheating only happens after extended stop and go driving.

I tune while its at good operating temp and just recently I bumped up my fuel pressure and started some learns. Now that I got the vortech supercharger in I raised my base FP on the 454 tbi with 80" injectors to about 30 psi (according to my liquid gauge). Previously it was at about 25 lbs and my DC was still exceeding the 100's.

Now it starts to jump past 85% after about 4400 RPMs... The DC% is going all the way to 180-190% when the RPMs reach 5500 RPMs... This sounds really bad to me although my AFR is at 10.0 reading from the WB.

Now that its VRFPR I find it funny that the DC is going so high...when the engine was N/A with 18lbs static fuel pressure it would not go past 100% ... will a SC really bump things up this much or could the default boost parameters in my tune just be over compensating with too much fuel now that it sees boost due to the 2bar map? ... guess this would also explain the 10.0 AFR.

I uploaded a datalog screenshot... and ideas?

Thank you!

Ronny

iTrader: (1)

The WB should be very accurate assuiming it was calibrated. Does the WB show realistic numbers under light load(cruise)? If so I bet it is accurrate.

You bring up a good question on the DC% reported. I wonder if it is showing accurrate or did you provide eroneous info in the tune making it report high. I know RBob prvides a calculator in Utility for BPC vs VAC. I would consider using a Mighty Vac and get the real numbers. Once over 0VAC I would think you need to bring in + pressure with another devise. I plan on doing just that this summer. I have an Aeromotive 13301 VAFPR.

ownor

iTrader: (5)

you might have something funky going on with your NBO2 setup. look at the "O2 mv", there are some data points where you'll find it at .6xx or one even at .430 volts, which imho could be the culprit to make the commanded AFR and hence the DC that much higher. if i'm not mistaken these ecms, when in OL for WOT, will check O2 voltage and it shouldn't be any leaner than say 0.9V or whatever the set limit is, otherwise it will add fuel.
you can also dump that log to csv or excel and look at the "AFR" column, which displays the commanded AFR. i would suspect that this would be much higher after the lean voltages occur at the NB O2.

edit: just more of a routine question, but you did enable the right bits for the 2 bar MAP, and not 3 bar? and also might wanna recheck if all the BPC tables are correct for boost, and maybe BST tables. haven't messed with these yet tho.

Ronny

iTrader: (1)

I assumed poster has a gauge seperate from EBL reporting? Possibly not.

That may be an issue as well. EBL not reporting real A/f. My WB does not report to EBL. It goes onto Innovate controller memory or shows on pillar gauge updating ever .5 sec or so.

I have 75 lbs inj(aka 80) at 21 lbs FP and show 85% DC in EBL in PE (12.8)being NA. I can see boost needing a lot more. I read recently fuel demand could double for large blowers.

RBob

iTrader: (1)

Once the injectors are at 100% DC they are open all of the time. The DC is a calculated value based on RPM and the injector PW.

With the AFR being so low you need to reduce the values in the boost fuel multiplier table. This will also lower the injector duty cycle. But that still needs to be in the 85% area.

Note that you can put negative values in the boost fuel multiplier table. This is sometimes required with systems that are as efficient.

The BLM at 113 isn't helping either. As when inn PE mode it is lower then 128, 128 is used.

RBob.

dirtyracer64

I have a couple questions about an issue, well maybe more of an annoyance about the idle quality of my new motor.

First off, this is what I'm working with.....

92 Z28 original 350 TPI/auto
Motor is a 355 1pc rms
ProComp 215's w/64cc combustion chambers
Forged flat top 10.1:1 compression
HSR for std SBC heads w/twin 58mm TB
30#/hr injectors
Howard's hyd roller 294 302 adv duration .550+ lift w/1.6 rockers
1.6 roller rockers
Hooker shorty headers into hooker/custom fabbed ypipe/midpipe into 4" Mufflex catback with Magnaflow race muffler.

Here's my problem. I have it idling at about 750rpm and has a manifold pressure at around 60-65kpa once at operating temp and shows on the WUD a WB AFR of about 13.0-13.3:1. It seems to idle....fair. Sometimes though, maybe every 15-20secs it will seem to faulter slightly, WUD shows a instantaneous drop to 45kpa or so and a momentary rpm jump to 950-1000rpms. Curiously though at the same instant the Launch Mode indicator light on the WUD comes on. The timing doesn't jump nor do the IAC steps jump.

I tried to find this anamoly on the datalog, but when the time stamp is looked up on the log, it's not picking it up for some reason.

Anybody have a clue what might be causing this?

Given my engine combination, does the 750rpm @ 60-65kpa 13.0:1 AFR sound reasonably tuned at idle or do you see it needing improvement still?

Thx guys!

RBob

iTrader: (1)

With that much cam a higher idle speed can be helpful. Can also set the open loop for idle option flag. That will prevent proportional gains along with the INT moving.

Option Word 1 - Bit 2 - OpIdl

For launch mode, it is likely tripping up on the delta MAP parameter, this one:

LM - Delta MAP Threshold Enter

Set it higher, say even 10 KPa.

The 60 - 65 KPa at 750 RPM is about right. Try setting the idle to 800 RPM and see how it is.

When data logging tapping the space bar places markers in the data stream. These can be search in the Analysis display via the Find Mark button. They show up as lines highlighted in green.

RBob.

dirtyracer64

Thx for the info Rbob! I'll make the adjustments!

Once that's done I'll work on the cold start and running from cold start to operating temp parameters. It's runs fairly rough til about 160* cts.

Thx Again!

Napster134

Ronny:

The WB values look pretty decent at Light load and cruise... I did some WB VE learns and they are starting to look much better although DC is still exceeding 100%.

I used the calculator Rbob provided me with to calculate those values (Vac Ref for 0-100map and non vac ref past 100map due to the boost). My values are actually a bit higher than the calculator recommends ... about a 30point difference. The calculator recommends a min of 78 & max of 108. My min is at 113 and my max is 143... I heard this aint much of a big deal since these are used as reference values but could be wrong?

I have the same Aeromotive as you too!

Ownor:

I noticed that too but I remember that on that run my tbi stopped to chug a bit in the middle of the WOT run...bad example to post. I dont know why but could have been because the tune was really off since I didnt do any WB learns after adjusting the FP so hopefully thats where that hickup came from. I'm going to try that excel spreedsheet thing... I didnt know there was more info behind what the EBL analysis showed... thats pretty cool!

Double checked just now... I have the "Option Word 2 - Bit 3 - 2-Bar" checked off and the 3bar option right above it is unchecked.

Ronny:

I do have the WB TT1 controller and what I like to do is plug that into my laptop first before I plug the EBL in to make sure its working by itself... then once I verify that the WB AFR needle is moving around on the TT1 software around I plug the EBL in... I have the EBL getting the WB info from the com port its setup on.

Hopefully boost doesnt make me switch injection systems :/

RBob:

I really hope thats where the answer is at... I noticed those boost PW tables are pretty high with values near 13-16% where I'm starting to see the extreme DC's. This would make sence since the boost SA tables were so dramatic that the car felt completely powerless as these tables were taking 10 degrees of SA when seeing boost. They must have really wanted to make sure someone didnt blow up their engine with these pretunes lol. If these values really mean that the PW is being increased by 16% then I'd be pretty convinced that this boost tables could be the culprit... hopefully!

I'll try to decrease those a bit and see what the DC's start doing.

Here's a few more screenshots of what things look like after decreasing the FP back down to 24psi and running some WB VE learns. (Couldnt stand the strong fuel smell with the FP near 30) The learns seemed to have bumped the AFR to something a lil more reasonable.

Now that I think about it... I think I'm going to be OK as far as my setup goes... correct me if I'm wrong but if I was truly running out of fuel then wouldnt by AFR be leaning out? Instead its too rich?

Thanks for all the help everyone!!

RBob

iTrader: (1)

Yes, if there wasn't enough fuel the engine would be going lean. Note that the latest WUD's and documents are now available on our web site, on the Updates page.

RBob.

Ronny

iTrader: (1)

13 min 53 sec in log....160% DC and a WB read of 12.5/1 does not add up unless the injector is open all the time and can just maintain the A/F you are seeing. No control over the injector by ECM yet it just makes the 12.5/1 by dumb luck.

I see you have plenty of fuel with a Walbro 255. You really need to crank up the fuel pressure.

How is it you are only at 190-199 grams/sec on airflow?

Is that max the EBL can measure?

I guess not. I just pulled a datalog done this AM. I was at 229 Gms/sec at 4900 rpms 100% TPS 90 MAP 91 MPH. And I dont have a blower?

Napster134

Well I think it comes back to that DC value being only a "calculated" rather than a realistically calculated value but im not sure...

The FP is at about 25 base so it should be jumping up higher under boost at a 1:1 ratio

as far as the grams/sec values go... What do these mean and what are they calculated from ?

Napster134

Sounds exciting! Anything really cool I should know about as far as features or changes go ?! Ill download them when I'm home from work

Ronny

iTrader: (1)

You are right. I forgot the VAFPR add fuel under boost. I guess I never had to think about it. How much does it add? 1:1 ratio is what?

the grams/sec I believe is the rpms vs CID. air pump. Not sure if barometric press factors in? But boost is more BP....

RBob

iTrader: (1)

The injector DC% is the real value. It is straight forward math, based on the amount of time between the injector firings. At 95%, the injector is open 95% of the time between this firing and the next firing.

Once at or over 100% the injector is always open.

I agree with Ronnie, more fuel pressure is required. Looks like about 6 - 7 psi and the AFR is at 12.3 - 12.6. With the DC over 100%, there is no headroom to get the DC at 85%.

The gms/sec is not used in the fueling other then for the INTegrator and proportional gains logic. Which is why it is in the analysis displays. That value is required to get the proportional gains dialed in.

Note that once in boost the VRFPR just keeps the same injector flow rate, no increase. This is due to it being a blow through set up.

RBob.

Ronny

iTrader: (1)

Same injector flow rate?

IOW if you see 150 MAP kpa maximum then you up fuel pressure and adjust BPC(downward) to show 85% DC at that RPM/MAP ? If so would not the idle be an issue?

RBob

iTrader: (1)

Shouldn't, whenever not in boost any decrease in manifold pressure (higher vacuum) will also lower the fuel pressure.

RBob.

Ronny

iTrader: (1)

When the Aeromotive FPR sees the increase in manifold pressure at its diaphragm does it not respond with increasing fuel pressure as Napster suggested? Which increases the injector flow rate?

Conversely with more VAC less MAP it decreases FP (as we know).

RBob

iTrader: (1)

Yes, no. The fuel pressure will increase. However, being a blow-through set up so does the pressure on the outlet of the injectors. So the injectors continue to flow the same throughout the range of boost.

If it were a draw-through set up then the injector flow rate would increase as the fuel pressure increased.

RBob.

Cflick

DC is pretty straight forward, so hard to argue with.
We know that above 85% or so, the computer has lost control. ( due to the time it takes for the injector to physically open and close ) Let's call it V-fib. It needs a de-fib, badly, else engine damage is likely.
We know that at 100%, you've run out of fuel, regardless of any other suggestion.
Above 100% is a fictitious number. The computer is telling the injector to turn on again before it can tell it to turn off ! The injector physically can't. It has some suggestion of how much fuel ( pressure ) is lacking, but only a rough suggestion. You need more fuel.

At the other end, idle is much easier to deal with, and much less likely to melt pistons.
1% DC is fine.

ownor

iTrader: (5)

... is only true when assuming all the electronics are in good working order, because otherwise it might still be trying to enrichen the PE mixture thinking that it's running lean from a wacky O2 feedback, right?

ownor

iTrader: (5)

This is actually a very interesting post. AFAIK also any system that has its injectors after the throttle body (MPFI) by design requires a vacuum referencing FPR. If I'm not mistaken there is a pressure differential across the injector with one side (nozzle) being subjected to manifold pressure (read: vacuum in most NA conditions) and the other side to fuel rail pressure, whereas in a TBI system or any injectors before the throttle body will see "ported vacuum" at the nozzle tip?

Cflick

Um.....
Yes, and no.
Yes, a defective O2 sensor could cause the system to deliver a flood condition, in which case you haven't run out of fuel necessarily.
No, because regardless of anything else, an injector can only do static 100% on and no more.

Cflick

Um, no.

Correct, and that's the pressure differential that will determine the maximum flow rate, or the amount of fuel delivered for a given duty cycle.

TBI systems, the injector fuel pressure is pretty much the difference between the rail pressure and atmospheric. Standard gauge pressure.
Port injectors the real injector fuel pressure is the difference between the rail pressure and the absolute manifold pressure, which is *probably* less than atmospheric.

In any case, the VE table controls the duty cycle of the injectors relative to the amount of air the engine is ingesting. So long as the injectors remain within range, a duty cycle between ~1% at the low end, and below 85-90% at the high end ( depending on peak RPM top end ) the actual fuel pressure really doesn't matter.

An interesting side note is that the actual upper limit to the allowable injector duty cycle is dependent on the time it takes the injectors to open and close, which is a fixed period of time that does not change. As such, you can run closer to 100% at lower RPM.
If you red line at 2000, then 97% is probably fine, but if you red-line at 24000, then 80% is likely much too high.

The purpose of a vacuum regulated fuel pressure regulator, is idle !
At the high end, if you run out of fuel you have only two choices.
One, bigger injectors.
Two, higher fuel pressure.
At the low end, in the event the minimum duty cycle still delivers too much fuel, you have only two choices.
One smaller injectors. ( not compatible with top end )
Two, lower fuel pressure, easily dynamically achievable with a VFPR.

The VFPR dynamically extends the range of the injectors, *provided* the pump/pressure can flow enough fuel for the top end.
Whether the injector nozzle is before or after the throttle plates is irrelevant.
It simply causes a slightly different curve when you plot the VE table.

If all of your VE table is between 2% and 85%, and your O2 sensor ( wide or narrow ) shows a good AFR under all conditions, you don't need a VFPR regardless of what type or where your injectors are located.

ownor

iTrader: (5)

i'm with you here on that, sure.
in general, i didn't seek to express any offense by my posts but instead interest on the topic, so please bear with the necessity of explaining things to me as an intellectual challenge

Imho that would be the exact reason for a PFI system to require a VRFPR. Two cases for example, assuming 4.0 bar rail pressure (about 59 psi for you non-metric guys ..or times 100 for kPa = 400 kPa) and a non-referencing TBI-style fuel pressure regulator, hence static fuel pressure over all conditions at the injector feeds; at atmospheric manifold pressure -> pressure differential = 400 kPa.

Engine at WOT, assume 100 kPa (atmospheric) MAP, or no vacuum. Port injectors will flow at a pressure of 400 kPa. this would be about the same as a gauge measurement of the rail pressure, because gauges are usually calibrated to show the pressure differential from the measured pressure to ambient pressure.

Engine idling, say you have 30 kPa absolute manifold pressure (MAP), atmospheric pressure is still 100 kPa (so 30 MAP = 70 VAC). Port injectors will effectively flow MORE, whatever they can put out at pressure differential of 470 kPa (we have 70 kPa less than atmospheric in the manifold!).

hence idle fuel flow would be bigger than at WOT. not making any sense to me (and probably most engine/EFI designers at the OEMs, too.. every PFI engine i've looked at so far - that might not be a too big number - they all had a VRFPR).

VRFPR PFI: Setting 400 kPa "static" fuel pressure at atmospheric conditions with engine off.
Results in pressure differentials of 400 kPa at idle and 400 kPa at WOT, because the pressure differential is REFERENCED to manifold pressure (vacuum) and NOT ambient (which is what it would be set at with engine off and a simple TBI/non-referencing FPR). the pressure differential between rail and manifold will actually track the manifold pressure and not fixed to ambient.

The TBI system will flow pretty much the same regardless of MAP, without a VRFPR. The PFI system won't.

Does that sound viable? I might be completely wrong.
Just feel free to correct me if applicable, I'm always keen on learning. Sorry for the metric units :P

edit, in regs to the rest of your posts there are some very good points made concering the merits of a VRFPR and injector DC issues related to engine speed timings.

Cflick

Methinks you're over-analyzing.

An injector is a mechanical device.
It takes a certain amount of time for the poppet to move.
When an injector is commanded on, there is a finite period of time for the poppet to traverse the distance between closed and opened. During that period, the injector flows some what less than it's rating, but more than none. When the injector is commanded to close, the reverse happens.

The injector requires the fuel pressure to be higher at the fuel rail than it is at the exhaust port of the injector. How much higher is only secondary. It needs to be enough to obtain the required flow. That's all.

At high speeds, somewhere between 80 and ~95% duty cycle, there isn't enough time for the injector to close. It merely flutters somewhere in the middle, flowing some unknown and uncontrollable value less than its rating. The engine goes dangerously lean.
At even higher duty cycles, there isn't time for the poppet to move at all. The injector remains full open. Goes "static" and flows everything it can, which is generally a LOT of fuel. Again, we've lost control. The engine usually goes rich.
The point is that control is lost. The ECM is not controlling fuel no matter what. AFR is random. Bad things can happen quickly.

One solution is bigger injectors, so that we have enough time for them to open a more brief period and still deliver enough fuel, AND still have enough time remaining to close them. We retain control of the fuel flow.
Another solution is to increase fuel pressure for the same effect.

Theoretically, if RPM is high enough, there simply isn't enough time for the poppet to move at all. At that speed, a different fueling system would be required.
Multi-port, for instance, so that each individual injector has a great deal more time to work.

At the low end, we have the same situation in reverse. The injector is commanded to close even before it's open, so it flutters somewhere in the middle. The AFR goes wacko, the engine stumbles and may even die. We may even get into a situation where we're commanding the injector closed before it can open at all, and they again go static, but closed. Fuel goes to zero, and bad things happen.
One solution is smaller injectors. Another is lower pressure. In both cases to reduce the fuel into the range the injector can control.
Perhaps multi-port, so that each individual injector can be much smaller, and so have much more time to work.

The purpose of the VFPR is to reduce fuel to the injector, so that we have enough time for the injector to open before we command it closed, allowing us to retain control of the fuel flow. The injector can remain open longer, allowing time to command it closed.

Note than in none of this do I mention the fuel pressure relative to anything other than the time it takes the injector poppet to move, because it doesn't matter !
What matters is time, and the inertia of the injector poppet.

The VFPR reduces fuel available to the injector at the low end, allowing a bigger injector that can be capable of handling the high end and at the same time allowing that bigger injector to stay within the finite range of control.
The absolute pressure at the exhaust port of the injector is irrelevant, as long as it's high enough for the fuel to atomize.

Therefore :
The requirement ( or convenience ) of adding a VFPR depends on whether or not the injector can be controlled over the full range of operation.
It does not depend on where the injector is located in the intake tract. Only whether we can accurately control the delivery of fuel over the entire range.
By regulating fuel pressure directly ( easy ) we are indirectly regulating the time available ( difficult ) to control the injector.

Does this make sense ?

ownor

iTrader: (5)

Cflick, I think I do have a rather good idea of the dynamics of the fuel injectors, including latencies for switching on, off and its relation to poppet inertia and injector actuation with duty cycle commanded and engine speed related requirements for timing constraints, etc. But I'm really sure your post is of merit to spreading knowledge and ideas about fuel injector control for other people

I was really focusing on the fuel pressure regulator or let's say, how much actually is dispensed by the opened injector. Based on pressure present at the tip and in the rail, and the injector location and its corresponding "ambient" pressure (locally). That was all in reference on RBob's post on how changes under boost (pressure over atmospheric) have an effect on fuel delivery.

.. which is exactly what i stated by my numerical example of the VRFPR, idle vs. WOT.

In my humble understanding of fluid dynamics, this statement is wrong. Given the exact same conditions (same amount of time, same opening ramp, poppet mass, engine speed and what not), there will be a difference in how much fuel can be dispensed by the injector! Because the pressure differential over the injector is what matters when it comes to calculating the actual amount of fuel delivered through the nozzle.

agreed

nope, this is the part I think is incorrect as stated above.

Yeah. Fuel pressure linked to MAP = engine load = fuel requirements sure does make it easier because time available can't be changed in most configurations. Time available as affected by mostly engine speed and poppet inertia, and maybe another parameter by switching latencies of the electronics. Oh yes and fuel injector quantity, or if you will "fuel injector resolution" as in how many injectors and how many cylinders
Think we are on to the same on this one at least ^^
Sorry folks for the long posts, hope this is not too misleading.

edit:
ha! buddy with the 84 with the LS1 in it (we're sharing this account sort of) just told me the returnless fuel delivery system of the 99-up LS1 only runs at static fuel pressure since the FPR is in tank... haven't messed with that before though so sorry i was unaware of such applications. but how does that work out then??

edit2:
dynamicefi.com states:

Cflick

Then I did misunderstand, to a point. ( dontcha love print vs a real in-person conversation ? )

You are absolutely correct, that the real fuel pressure is the pressure differential across the injector, which is seldom gauge pressure.
The injector is rated at X flow for Y pressure, across the injector itself.

SO, if you're running boost, then the gauge pressure across the injector is the rail pressure MINUS manifold pressure. It's the pressure across the injector that will determine how much fuel the injector can flow, regardless of what the gauge says.

In a normally aspirated port injected engine, the fuel pressure across the injector is always some-what higher than gauge pressure, so the injector *can* flow more fuel at idle than at WOT. Exactly opposite of desired. In a TBI system, real injector fuel pressure is always very close to gauge pressure.

In a blown engine, it's theoretically possible to get the manifold pressure higher than the fuel rail pressure, so that when the injector opens, the manifold pressure will blow air back into the fuel rail, and no fuel will be delivered at all.

All of the things I scribbled apply, *plus* the added problem of keeping fuel pressure *enough* above manifold pressure to flow adequate fuel under boost, *and* still being able to control the relatively minimal fuel requirements at idle.

There are a few ways to approach that problem. My choice would likely be a fuel pressure regulator referenced to absolute manifold pressure, with the injectors commonly available. ( which is a type of VRFPR ) And, a fairly high pressure high flow pump.

88gunmetalgta

iTrader: (1)

Still trying to track my cutting out issue down. What I've found so far is that the actual sensor voltage readings are not fluctuating as wildly as my WUD is saying they are! I haven't gotten a flicker of voltage to indicate a loose connection or bad ground. Every +12v pin and every ground pin stay rock solid even while the data logging shows voltage jumping around from 5-12, MAP, IAT, and CTS are all over the range, but with the DVOM on them, they seem rock solid.

What would cause the ECM to sense incorrectly if the sensor voltages themselves are correct? If I had a power/ground issue, I would expect to see the voltages varying as the reference voltage or ground resistance varies...

ownor

iTrader: (5)

Yeah well it happens, no prob Good points on the need for even higher fuel pressure when referencing boost in the manifold. But the point I still dont get is how the LS1 returnless tank system doesnt need a VRFPR. I would imagine there's far too much fuel at idle and not enough at high load/rpm? Maybe really good injectors (small poppet inertia) and actuation can solve that problem so that idle fueling is still consistent with very small DC, thus leaving enough fuel for the high DC sitations.

gunmetal, for me personally i would maybe consider the ECM being out of whack. could still be some weird kind of voltage level reference issue but it's strange since you tracked down all that with the voltmeter and it seems perfectly fine..

RBob

iTrader: (1)

ECM is likely intermittent. Can ship it back to us for repair or replacement.

RBob.

RBob

iTrader: (1)

{LS1 returnless tank system} There are a handful of large tables that handle the varying injector flow rates along with the varying injector compensations. The PCM knows the manifold pressure from the MAP sensor, so can compensate in real time.

RBob.

88gunmetalgta

iTrader: (1)

I went out again and checked sensor voltage. It is fluctuating, my volt meter is just too slow to pick it up. So back to square 1. Providing the ECM with known good power and grounds does not solve the issue.