Fuel Pressure Help

Fast_Mustang87 · Dec 25, 2007

Hey everyone, I'm having problems running rich with my 91 coupe. It's a 347 eagle stroker kit, Port and polished heads, Upgraded valve springs, Stock upper and lower, Crane cam 529 lift, Headers, Exhaust, ect. For some reason it's running rich and fowling spark plugs every now and then. It has a T-rex fuel pump also and stock 19# injectors with stock fuel regulator. I bought a adjustable fuel pressure regulator from BBK a week ago and i'm wanting to put that on soon. My question is, Would the stock regulator be my problem that im running rich? When i put the BBK regulator on what should i set the PSI to? Would i turn the PSI up or down? And why is it running rich? Any help would be great and thankfull!

86bluecobra · Dec 25, 2007

I believe you want 38-42 psi. As for it running rich well that could be a bunch of things. Have you checked for codes? It could be things like ect or air temp sensor. could be fuel pressure or a fowled injector on the cylinder that is fowling plugs. Run the codes you will get pointed in the right direction.

Fast_Mustang87 · Dec 25, 2007

No i havn't checked the codes yet but i'm going to. Like you said it could be anything. I'll check it out though. As far as setting the fuel pressure PSI i'll set it at 38psi and work my way up. Thanks for the info!

irish · Dec 25, 2007

19 lb injectors on a 347 with good heads? I am surprised you are rich.

2000xp8 · Dec 25, 2007

Explain your heads a little more.
Put the AFPR on, ditch the t rex for an intank 255, no reason to run the chance of losing an external pump and going superlean, on a car that has no need for an external pump. The sale of the t rex should more than pay for a walbro 255.
And i'd consider going to 24's, with the proper meter too.

I'm with irish, that combo should be lean, not rich. But at this point it's a mismatch anyway, get the right parts and start over.

Fast_Mustang87 · Dec 26, 2007

There E-7's that are port and polished. Yeah i'll prolly ditch the T-Rex and go with a BBK in tank. I believe it's running rich because it smells like gas when it comes out of the exhaust and my air/fuel ratio gauge is all the way on rich. I'm also looking into bigger injectors like you said and a meter as well but would 24's be enough fuel for my setup? Would a BBK 255lph be too big for my setup though? Also can you adjust them fuel pumps as well? Thanks everyone you have been helpfull!

2000xp8 · Dec 26, 2007

Since your heads are E7's 24's should do it, use a PMAS meter.
Get a walbro pump, walbro makes almost all pumps including the BBk, but is usually far far cheaper.
The fuel system on a foxbody mustang is return style, meaning the excess fuel goes back to the tank. So the pump doesn't adjust, just the regulator does.

Sounds like you have an a/f ratio gauge, the best idea is to just ignore it, it's just a light show.

Fast_Mustang87 · Dec 26, 2007

Sounds good, I hope this takes care of the problem. I just don't know why it's runnin rich but i'm going to get to the bottom of it. I have the fuel pressure regulator and i'm going to get some 24's, a meter, and a fuel pump soon. I hope this solves the problem! WHen i get the 255lph fuel pump on what should i set the fuel pressure to? Thanks alot!

v8only · Dec 27, 2007

those 19's are probably ok.....even with a 347, I doubt you're making over 300hp with that combo, and that stocker intake...

You seriously need to consider some good aftermarket heads and intake, it's killing you!!

as for the adjustable fuel pressure regulator, throw it in the garbage. They're useless. The stock ecu will compensate for fuel pressure regardless of where you put it at.

unless you go out and get a tune for it, it's not gonna do anything other than introduce more problems.

From your username it appears as if you have an 87???

I assume you've upgraded to mass air right?? If you're still running speed density, that's your problem.

Fast_Mustang87 · Dec 28, 2007

v8only said:
those 19's are probably ok.....even with a 347, I doubt you're making over 300hp with that combo, and that stocker intake...

You seriously need to consider some good aftermarket heads and intake, it's killing you!!

as for the adjustable fuel pressure regulator, throw it in the garbage. They're useless. The stock ecu will compensate for fuel pressure regardless of where you put it at.

unless you go out and get a tune for it, it's not gonna do anything other than introduce more problems.

From your username it appears as if you have an 87???

I assume you've upgraded to mass air right?? If you're still running speed density, that's your problem.

Thanks for the info, 87 was the year i was born and i have a 91 coupe. I'll end up geting the tune in the spring time when the weather gets warmer. Thanks for all the help

Foxfan88 · Oct 5, 2008

v8only said:
as for the adjustable fuel pressure regulator, throw it in the garbage. They're useless. The stock ecu will compensate for fuel pressure regardless of where you put it at.
QUOTE]

actually the EEC doesnt "compensate" for fuel pressure at all.

in closed loop operation where the EEC is trimming fuel delivery based on o2 feedback the EEC will correct for slight lean and rich conditions, the EEC can correctly up to 25% (12% in either direction)

but when you got WOT, the EEC pretty much goes blind and doesnt rely on feedback to trim fuel so its just dumping fuel into the engine according to what it thinks is right.

the stock EEC "thinks" that the stock injectors flow 19 lb/hr with stock fuel pressure which is around 39 psi, increasing the regulator pressure with no vaccum higher than 39 psi will result in more fuel. more pressure on the stock injectors results in more fuel at WOT

lowering it under 39 psi will mean less fuel.

v8only · Oct 5, 2008

i'll have to do more research, but it's a well known fact that the aftermarket regulators are junk without a tune.

I'll re-iterate my previous statement that the computer will tune it out with an adjustable fuel pressure regulator.

don't use one without a tune, it won't make a difference.

the computer is more than capable of controlling the amount of fuel pressure, and the flow through the injectors.

joel5.0 · Oct 6, 2008

Foxfan88 said:
v8only said:

as for the adjustable fuel pressure regulator, throw it in the garbage. They're useless. The stock ecu will compensate for fuel pressure regardless of where you put it at.

Click to expand...

actually the EEC doesnt "compensate" for fuel pressure at all.

in closed loop operation where the EEC is trimming fuel delivery based on o2 feedback the EEC will correct for slight lean and rich conditions, the EEC can correctly up to 25% (12% in either direction)

but when you got WOT, the EEC pretty much goes blind and doesnt rely on feedback to trim fuel so its just dumping fuel into the engine according to what it thinks is right.

the stock EEC "thinks" that the stock injectors flow 19 lb/hr with stock fuel pressure which is around 39 psi, increasing the regulator pressure with no vaccum higher than 39 psi will result in more fuel. more pressure on the stock injectors results in more fuel at WOT

lowering it under 39 psi will mean less fuel.

Actually..... it does compensate for fuel pressure, even though the O2's input is "ignored" in open loop, the system has alternate fuel control strategies to deal with that..... BTW, the calibrations in a GUFB strategy are based in a fuel pressure of 42 PSI, not 39 PSI.... reason why the acceptable FP specification window of SEFI systems is 35-45 PSI engine running. The A/F feedback to trim fuel pulse width while in open loop, is based on the other system inputs...... otherwise, the EEC-IV systems wouldn't have passed the emissions requirements of their time.

Even though WOT is an open loop based fuel control event, the adaptive strategy (learned when in close loop) does affect WOT fuel tables....... reason why any change in the fuel pressure, eventually gets canceled out by the adaptive strategy..... if it cannot correct it within its limitations, A/F control failure codes will be logged..... reason why running the self tests is key to ID the causes of any problems and verify A/F control is within the EEC "corrective" capabilities.

Foxfan88 · Oct 6, 2008

joel5.0 said:
Actually..... it does compensate for fuel pressure, even though the O2's input is "ignored" in open loop, the system has alternate fuel control strategies to deal with that..... BTW, the calibrations in a GUFB strategy are based in a fuel pressure of 42 PSI, not 39 PSI.... reason why the acceptable FP specification window of SEFI systems is 35-45 PSI engine running. The A/F feedback to trim fuel pulse width while in open loop, is based on the other system inputs...... otherwise, the EEC-IV systems wouldn't have passed the emissions requirements of their time.

Even though WOT is an open loop based fuel control event, the adaptive strategy (learned when in close loop) does affect WOT fuel tables....... reason why any change in the fuel pressure, eventually gets canceled out by the adaptive strategy..... if it cannot correct it within its limitations, A/F control failure codes will be logged..... reason why running the self tests is key to ID the causes of any problems and verify A/F control is within the EEC "corrective" capabilities.

adaptive strategy can only be applied to a condtion where adaptive strategy "learned" the correction right??

the EEC needs feedback to "learn" which are the o2s, in OL or WOT, there is no form of feedback for the EEC to use to correct any errors.

as far as i knew, adaptive control is only used during closed loop operation and the correction multiplier is only applied to those condtions from there on out in CL and the same condtion in OL. since the o2s are only useful for feedback around stoichiometric, there is no way for the EEC to know if its running rich or lean at WOT condtions, there is nothing to let the EEC know. thats why we need a WBo2 to log and manually adjust and correct the maf tranfers or inj slopes or w/e needs adjusting.

if i'm wrong then please explain to me how it works, i would like to know and understand as much as i can.

since i have been tuning with my tweecer. i have always disabled adaptive control to make tuning easier, i have a WBo2 and dont need KAMRFs to skew things up for me.

joel5.0 · Oct 6, 2008

Foxfan88 said:
adaptive strategy can only be applied to a condtion where adaptive strategy "learned" the correction right??

the EEC needs feedback to "learn" which are the o2s, in OL or WOT, there is no form of feedback for the EEC to use to correct any errors.

as far as i knew, adaptive control is only used during closed loop operation and the correction multiplier is only applied to those condtions from there on out in CL and the same condtion in OL. since the o2s are only useful for feedback around stoichiometric, there is no way for the EEC to know if its running rich or lean at WOT condtions, there is nothing to let the EEC know. thats why we need a WBo2 to log and manually adjust and correct the maf tranfers or inj slopes or w/e needs adjusting.

if i'm wrong then please explain to me how it works, i would like to know and understand as much as i can.

since i have been tuning with my tweecer. i have always disabled adaptive control to make tuning easier, i have a WBo2 and dont need KAMRFs to skew things up for me.

Adaptive is "learned" under close loop conditions, but also applied to open loop conditions.... sort of a way to anticipate or predict system behavior.

In OBD-I and OBD-II systems it is known as the "LTFT" or Long Term Fuel Trim correction factor.... add a 1 and 2 suffx for bank ID; and "STFT" or Short Term Fuel Trim correction....... same as INT or INTegrator for short term and BLM or Block Learn Multiplier or LTFT for OBD-I GM's..... they had to comply with the same emissions rules.

Even though no A/F feedback is present under OL or WOT conditions..... LTFT trims are applied to both OL conditions via functions in the logic. This is also the main reason why, in OBD-II systems, a "readiness state check" is required......IOW, a minimum adaptive strategy applied for an OBD-II system to be able to pass emissions.

By not allowing adaptive to be used + not tuning it..... you literally have an A/F control system that compares with a carburetor....... you are not using/allowing the EEC/computer adaptability features to cancel out any non-EEC variables that could/will affect A/F & spark control.

I worked on a SC SN95 CBAZA setup, and I used the STFT/LTFT values to center the tune..... no matter what the non-EEC variables changed (FP, altitude, etc).... the fuel trim corrections stayed within ±4% of the tables targets. This made sure it stayed within its ±12.5% (higher in the CBAZA strategy) fuel trim correction window. We were at 12 PSI boost and used the OEM FP regulator w/out any problems.

Foxfan88 · Oct 6, 2008

makes more sense now, i also did some more reading on it and i guess i stand corrected.

v8only · Oct 10, 2008

wow. How did you guys learn all this?? I'm pretty well off with my mustang knoweledge, but this passes my capabilities.

Should I pick up a tweecer?? I'd love to learn more on this subject, and just reading isn't working for me

joel5.0 · Oct 10, 2008

v8only said:
wow. How did you guys learn all this?? I'm pretty well off with my mustang knoweledge, but this passes my capabilities.

Should I pick up a tweecer?? I'd love to learn more on this subject, and just reading isn't working for me

Yep... or a Moates gear. When you have to deal with engine/ECU/TCU/ABS/etc/etc problems every day.....you need to make sure you don't cause a customer to spend his hard earned $$ in unneeded replacement parts due to a bad diagnostic, and the only way to do that, is understanding what you're trying to fix.

Fuel Pressure Help

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