Another dumb fuel pressure question.

[ViolatorTA]

Looking through the stock tunes I have DL'd I was comparing 02 TA IFR's to 02 Vette IFR's. Now as far as a know and with all the replacement part numbers, both use the same injectors and both are rated at the same fuel pressure. What I noticed was a difference in IFR values, though minimal, they are different.

So my question is. If flow rates are determined by fuel pressure and rated flow, why would these be different through GM cals? Could it be that this was part of GM's detuning of the F-Body to keep HP down from the near identical LS1 in the Vette? Could this actually skew the figures of IFR spreadsheets out there? ok...3 questions:nixweiss:

I ask mainly because no matter what combination of numbers I put into the spreadsheet that are possible for my injectors, be it 43.5 psi/58 psi or measured 61psi along with manufacture's rated lbs at 43.5 or 58, my 30kpa MAP row in logs stays extremely rich even with a nice smoothed VE table. I have even tried sspddmn's VE with -5/+5% differences in entire table. Figured his would be safe since cam is almost the same and got the same results just a little rich across the board from 800-3600rpms.

Came someone shed light on my non-experience. Just trying to increase that learning curve.

:cheers:

[vatman02]

just my .02. may be it is because of the cams being a bit different one has different fueling needs perhaps this is why GM used such a small injector that they are barely big enough to run a stock motor @ 80% duty cycle it is more dificult to control the injectors at such low map values. i was never able to dial in my 60's at low map pressures afr would be 10.9:1 no matter what i did that wont pass the sniffer so i opted for smaller ones

[joecar]

Looking through the stock tunes I have DL'd I was comparing 02 TA IFR's to 02 Vette IFR's. Now as far as a know and with all the replacement part numbers, both use the same injectors and both are rated at the same fuel pressure. What I noticed was a difference in IFR values, though minimal, they are different.

So my question is. If flow rates are determined by fuel pressure and rated flow, why would these be different through GM cals? Could it be that this was part of GM's detuning of the F-Body to keep HP down from the near identical LS1 in the Vette? Could this actually skew the figures of IFR spreadsheets out there? ... Can you post the two IFR tables (paste the values into a reply) identifying which one is the ZO6 and which is the TA...

:)

[ViolatorTA]

I'll get them up as soon as I return. It's not a Z06, it's just a base Vette compared to a TA which is what made me question it more. Z06 I may think differently.

[dfe1]

Injector flow rate is only part of the equation. Take a look at B3701- Pulse Width Voltage Adjustment. The values for Corvette and Camaro are different, so it stands to reason that the IFR values are also different. I think the problem you're having is an effect of the cam. Volumetric efficiency is so low at low rpm that you have to come way back on fuel.

[ViolatorTA]

I think you are correct. My last log shows every single cell from 30kpa down in fuel trim cell #21 regardless of rpm. What would be the best approach to set the VE table at for 15 to 30kpa?

[dfe1]

I think you are correct. My last log shows every single cell from 30kpa down in fuel trim cell #21 regardless of rpm. What would be the best approach to set the VE table at for 15 to 30kpa? I've always found that the best approach is to "listen" to the engine. If it says it's too rich, it is too rich-- keep reducing the data in the appropriate VE cells until the air/fuel ratio is where it should be (I assume you're using a wide band). I'm running a 232/236 cam and the VE table takes a sharp dive below 2000 rpm and below 35 kPa. It's not particularly pretty at the lower end, but AFRs are within 1% of commanded everywhere. Are you running open loop?

[ViolatorTA]

Yes. Running open loop with WB. I begin to worry about going too low in those cells in fear of hurting something and having a false reading.

[vatman02]

I've always found that the best approach is to "listen" to the engine. If it says it's too rich, it is too rich-- keep reducing the data in the appropriate VE cells until the air/fuel ratio is where it should be (I assume you're using a wide band). I'm running a 232/236 cam and the VE table takes a sharp dive below 2000 rpm and below 35 kPa. It's not particularly pretty at the lower end, but AFRs are within 1% of commanded everywhere. Are you running open loop?

i tried this with my 60#ers i had the low map/rpm areas down to 10 and it didnt change a thing it still ran at 10.9:1:bash: i hope i wont have the same problem with my new 42's

[dfe1]

Yes. Running open loop with WB. I begin to worry about going too low in those cells in fear of hurting something and having a false reading.
It really shouldn't be a problem as long as logged pulse width is longer than minimum pulse width. Also, if you get more aggressive with DFCO, those areas of the VE map won't be an issue because in most cases, fuel will be shut off.

[ViolatorTA]

Should I be logging with DFCO on or off. Tutorial says off. I know I seen some IPWs that I logged earlier that were .55 if you clicked the down arrow on the map. The averages were all above my lowest pw settings.


Vatman.....That is the size injector I'm messing with now.

[dfe1]

Obviously, you have ot log with DFCO off if you're trying to check air/fuel ratios, but a lot of the data in the MAP will become irrelevant when DFCO kicks in. I'd advise you to get AFRs in the low MAP/low rpm areas close to commanded, but don't go nuts with it if you plan to reactivate DFCO.

[ViolatorTA]

What would you consider close? I'm seeing .89 to .92 in areas where FTC's are all 21.

[ViolatorTA]

Ran a test tune, now I'm skeptical.

[RacerChris]

i tried this with my 60#ers i had the low map/rpm areas down to 10 and it didnt change a thing it still ran at 10.9:1:bash: i hope i wont have the same problem with my new 42's

I would check your injectors because I run the Mototron 60lb injectors with a 222/224 cam and my VE in the lower area doesnt go below 22%.
Just a thought!

[redhardsupra]

i tried this with my 60#ers i had the low map/rpm areas down to 10 and it didnt change a thing it still ran at 10.9:1:bash: i hope i wont have the same problem with my new 42's
that just means you've hit some sort of 'floor' and it's not able to dump less fuel than what will give you 10.9. easiest way to fix it is to raise your idle (if that's your problem, usually it is) so it gets more air, so the minimal amount of fuel you give it matches it.

[redhardsupra]

Injector flow rate is only part of the equation. Take a look at B3701- Pulse Width Voltage Adjustment. The values for Corvette and Camaro are different, so it stands to reason that the IFR values are also different. I think the problem you're having is an effect of the cam. Volumetric efficiency is so low at low rpm that you have to come way back on fuel.
do you have a method of arriving at a sane(er) pulse width voltage adjustments, short pulse, default pulse, any of that stuff? i'm extremely interested in these, and i found next to no info on it.

[dfe1]

do you have a method of arriving at a sane(er) pulse width voltage adjustments, short pulse, default pulse, any of that stuff? i'm extremely interested in these, and i found next to no info on it. Based on my experience with GM engineering, I don't think sanity is an option. In the case of the Corvette versus Camaro IFRs the operating systems for both vehicles were the same (12212156) which means the differences are a result of the preferences of the engineers doing the calibrating. There may also be some esoteric data that indicates marginally different flow characteristics for the fuel systems in each vehicle, but I doubt it. I think if you did an in-depth analysis, you'd find two different methods of achieving the same results. That's why I always go back to "listening" to the engine. It doesn't care who did the calibration or how the final results were achieved. All it cares about is receiving air and fuel in the proper amounts. If you arbitrarily assume that a Corvette calibration is "better" than a Camaro calibration, and use a portion of it (like the IFR table) you're going to shoot yourself in the foot more often than not. In regards to pulse width adjustments, I haven't seen any data that inspires any kind of confidence. A friend of mine has an injector flow bench, and we're going to run a set of injectors, vary the voltage and actually measure the fuel flow. I suspect that we'll find our results match neither those in the Corvette or Camaro tables. Obviously, voltage variations affect each type of injector somewhat differently, so we're going to check several types of injectors to see how wide the variations are. I'll post more information when I have it.

[ViolatorTA]

I believe the 2 methods of getting there. Looking carefully through 02 Vette and TA tunes with the same OS's but diff. cals I noticed these major changes.

VE table
IPW voltage adj
IFR which averages 0.011+
Min IPW which is 0.015- across the board
Default Min. IPW 0.015-/0-800 3200-8000rpm
0.182-/1200-2800rpm
Small pulse adj which varies

IAC effective area
Desired airflow(could cancel out due to diff. air ducting.)
TC in gear- large difference
TF airflow

All are % difference


Thats just some. Seems to me GM used inj flow,airflow and ve changes to get there, just different ways of calculating each. Charge temp values are the same but who knows what's hidden.

I'm beginning to believe Base, TC and TF play a big role in these equations but then again, I think too much. Could it really be that simple and too much thought has been put into the proper way to tune?

[joecar]

... Seems to me GM used inj flow,airflow and ve changes to get there, just different ways of calculating each. Charge temp values are the same but who knows what's hidden.

I'm beginning to believe Base, TC and TF play a big role in these equations but then again, I think too much. Could it really be that simple and too much thought has been put into the proper way to tune?That's what it seems to me... different ways of adding different amounts of the components to obtain the same result.

[vatman02]

I would check your injectors because I run the Mototron 60lb injectors with a 222/224 cam and my VE in the lower area doesnt go below 22%.
Just a thought!

i think alot of the problem is the altitude i have 20% less baro here thus 20% less air anyway i just sold the 60's and am waiting for some 42's

[redhardsupra]

That's what it seems to me... different ways of adding different amounts of the components to obtain the same result.
yes, but some of these tables describe very particular behaviors, like the short pulse issue is very weird and does not follow a normal behavior, so it's not a simple lookup but lookup with modifiers. it would be nice if they just made it into a one bigger model instead of go case by case, but i guess this is simpler to deal with from a simple cpu's point of view.

i could make my IFR to be artificially lower at the MAP/MANVAC where i idle just to produce the right idle, but then if i happen to be driving at the same manvac (but different RPM, so it yields a different VE, thus airmass!) then my fueling is going to be off because it's dumping more than supposed to. and you're chasing your tail. again.

there's no point in avoiding understanding of these issues. we cannot ignore them. as much as i'd like to ignore gravity every time fall on my ass, it's not going to go away, so might as well learn to anticipate it.

[dfe1]

It's a mistake to think that GM engineering always operates on consistent, logical principals. In many instances, I've found that the personal preferences of the enginer in charge of a particuar project are the controlling factor. This is fairly apparent if you examine the many about-faces GM has made over the years. One that comes to mind is the reverse cooling system used in the LT1 engine series. I remember the cooling system engineer showing all types of documention to illustrate the superiority of reverse cooling. That was in 1991. By 1996, when the LS1 engine was introduced, reverse cooling had gone the way of carburetion.

Calibration practices are similarly random, based on the preferences of the individual calibration engineer. I fully agree with RHS that it would be helpful if we had a full understanding of all the modifiers, but I'm not so sure that we'll find a consistent enough pattern to uncover the method to the madness. I tend to think that a lot of modifiers are included to address unique conditions which may not exist in some engine combinations. (Have you ever noticed that a number of tables are filled with 0s or 1s in some stock calibrations?) I'm farily certain that some values are the result of altering one calibration to fit a different engine/drivetrain/vehicle combination.

[redhardsupra]

i dont want a consistant pattern, i just want a consistant method to reveal any patterns we need ;)

lately i've been 'entertaining' myself using some general modeling tools like multi-variable non-linear regression to optimize parameters we cannot measure empirically. it seems to work, i just need some time to verify it.

I haven't used it on short pulse stuff yet, but it'd be interesting to see if it'd work. anyone got logs with very pronounced problems due to the short pulse not being calibrated for aftermarket injectors?

[ViolatorTA]

pronounced such as?

[vatman02]

might this be what you are looking for if so i will post it up i didnt log ibpw for the one that has the 60# injectors the other is the stock 28's what i dont get is why the gm injector flow and the calculated flow dont match when i was logging at idle (and didn't save) i was seeing pulse widths of 1.6-1.8

[vatman02]

man i suck at this i cant get the pics up so i posted both loggs you can see what i was saying without even pushing play