spcearle

ok was doin some work on my car today and disconnected battery...when i hooked it back up i noticed my fuel pressure gage reading only about 32psi..after running it and driving it readjusted to 43psi now heres my question...the car has always run rich on me and i have an afpr....should i adj the pressure on that to lean it out or vise versa...does anyof this make sence...could my computer be addng to much fuel to composate for the pressure at the regulater ,,,if so which way should i be turnin this sucker and to what...should i eset the comp again and bring it to the comp setting of 43psi or would i want higher to trick it into leaning out...any input would be great....thought i was just dealing with a overheating issue on the car now i have a fuel and overheating issue

RamAir95TA

Adjusting the fuel pressure by itself is a fruitless operation as the PCM will quickly see the change in target AFR, resulting in a change in injector pulse width.

How do you know your car is running rich? I see you have some substantial mods - what are you using for tuning?

spcearle

strong smell of fuel and black plugs.....the tune on the car right now is a mad mail tune ....looking for a place now and saving up some cash to get a dyno tune done....so what your saying is the comp wont add air or fuel to adjust to the comp setting just adjust the pulse in the injectors to get to that setting

Injuneer

The fuel pressure was 32psi under what conditions? At idle, with the vacuum compensation line connected, that may not be far from the acceptable pressure level. Take the vacuum line off, and see what the pressure is without the vacuum compensation. That's when it's supposed to read 43.5psi. GM accepts anything in the range of 41-47psi as withing spec.

At WOT/max RPM, you should not drop below 40psi.

If you are running at 43.5psi, WITH the vacuum line connected, the AFPR is set too high.

The computer bases the injector pulse width on the injector rating that it is programmed with. When the pressure drops below rated, the injector flows less fuel than the PCM thinks it will. The O2 sensor indicates "lean", the PCM starts increasing the long term fuel corrections (BLM's) until the A/F ratio returns to the hard-coded 14.7:1 closed loop value.

If you reduce pressure to lean it out, the PCM increases the BLM's in closed loop. Then when you go WOT (power enrichment mode), the PCM uses the elevated BLM's to fuel the engine, and it runs as rich as it did before you tried to fool the PCM by lowering the fuel pressure.

Tune with the PCM, not with the AFPR.

spcearle

i think your misunderstanding my original post ...now im trying to right a poss wrong....i reset my comp when i diconncted my battery...when i started the car up the pressure was only at 32 or so....after a while of running and driving the pressure reset to about 43 or so.....i had my comp tuned to the setting..i dont tune with the regulater..its been on the car now for a cpl years un touched,....what i was asking is if it might have something to do with the richness i am bburning.....how can i set the thing right or am i not doing anything difference making with it at all......just wondering if with the thing set where it is at if the car is forcing in more fuel by thinking it is running to lean....i have the thing on the car only because at the time my stock was shot/got a good deal on it/and it enables me a port to hook up my electric fp gauge and still have the schradder valve for mechanical tests....also at 1/2 to full throttle wacks my fp rises to about 50psi.....thats all i'm trying to figure out...should i reset comp again and adjust the fpr till its at 43 or so or go higher this all being with the vacoom line hooked up

RamAir95TA

How do you know you are running rich? Most every mail-order tune on an aggressive setup will always be rich for safety's sake. I would have it scanned and see what you come up with. You might just need a good dyno-tune.

spcearle

burning fuel smell...black plugs after a few runs is all i know so i cant possitively say i am but those are usually good signs...and yes i deff need a dyno tune the mail order was just supposed to be a temporary thing..now about 4 yearslater still a tempory just a very long one...lol

Injuneer

The PCM can't "reset" the fuel pressure. The PCM has no way to know what the fuel pressure is.

Again, if your fuel pressure gauge changed from 32 to 43, something happened in the fuel system. The pressure should always stay the same EXCEPT for the vacuum compensation.

Again... when your fuel pressure gauge said "43", what were the operating conditions? Full-temperature idle? .... vacuum line connected?

If as you indicated, the PCM was tuned for injectors that were flow rated at 43psi, why would it be getting too much fuel when the system is running at 43psi.... unless you are ignoring the whole concept of vacuum compensation, and the need to maintain the DIFFERENTIAL pressure (rail pressure minus manifold pressure), not the rail pressure.

All you had to do was answer the original question - "The fuel pressure was 32psi under what conditions?"

You set the pressure WITH THE VACUUM LINE DISCONNECTED.

I'll risk asking another question - is you AFPR made by Aeromotive?

spcearle

and as i stated b4 the car was off for prob 18hrs so it was cold....the battery was diconnected ...when i reconnected the battery with everything hooked up normally meaning the vacoom line going to th regulater it was at 32....i ran the car at idle for about 15mins bleeding my coolant system....drove the car around town for about 20 mins....car was well into operating temp and the fuel pressure rose to normal press.....when the regulater was installed back in 05 i cant recall how it was adjusted...ive only had it removed a cpl times since when doing stuff with my injecters.....i'm not trying to be a dumb *** here thats why i'm asking cause i know there are people here that know more about these systems ....so i am trying to answer your questions at the get go..i guess people just arent understanding my explanation...and yes it is an aeromotive...

Injuneer

The Aeromotive LT1 AFPR has a very high failure rate.

The pressure should not be changing based on engine temperature, how long the engine was running, etc. The AFPR should hold it at the set pressure (minus vacuum). You need to find out why the pressure is jumping around.

spcearle

i know thats why i'm on here looking for advise and direction

Injuneer

First you have to set the pressure correctly. Why not start there?

spcearle

once i get the car back from the shop if its still running which is a whole nother issue and story...i'm gonna go through the steps of readjusting the pressure to where its suppose to be and see if it stays put and go from there...mind you i never adjusted it to be low and i know it has a problemsome afpr in it but right now i'm tryin to make do with the means that i have...kinda low on funds from being outta work and starting school so trying not to throw parts or repairs into it if i dont have to right away ...

spcearle

i readjusted my fp with the vacuum off to about 43-5 psi.....i noticed it really doesnt make any difference in er with the line connected or not but thenagain it might also be my gauge is no longer accurate which used to be right on the money with a mechanical but elctric stuff does fail after time so i'll track down a mechanical to comfirm....my pressure stays right around the 43 area with maybe a 1 or 2 pound diff across the throttle.....monday i'll bring er to a real shop around the cxorner and have them drain and flush out everything right to see if that helps.....one thing i did notice though was at the c100 connector there were 2 wires not connected heading towards the front half of the harness a brown and light blue and at the pcm side the 2 browns may be switched in the wrong spots from when i did the wire mod but it makes no diff with how it runs with everything hooked up...basically this all started with an overheat issue and then me being a complete dumb *** and bringing it to pepboys for a simple coolant flush and them messing it up even more

Injuneer

Was there a vacuum at the end of the line from the manifold to the AFPR? Was that vacuum line cracked or damaged? Was there any fuel in the vacuum line?

If you have manifold vacuum at the end of the line, the AFPR is not working correctly.