hey everyone, gonna try to sum it up short as possible..

I had a vortech kit on my car for a while and everything ran great the whole time..All of a sudden one night recently i look at my a/f gauge and it is lean..If i lugged it down the a/f was on point until 3500 rpm then instantly lean, from 11's straight into the 13's..I figured i needed to re-tune and add more fuel or something due to me finding a few boost leaks and fixing them, figured i just needed more fuel..I was going to take the kit off at the end of summer anyway so this just gave me reason to so i could narrow down inline fuel pump problem or fmu problem or tuning problem due to fixing boost leaks..I took the kit off which is now sold and long gone and the car is still lean...I tested the sensor on my gauge and it is working correctly...

Now the car is back to n/a just bolt on intake and exhaust, etc...Still the same deal though so it had nothing to do with the vortech kit, if i lug it down and get on it in any gear it is fine but as soon as i get to 3500 rpm it is instantly lean..a/f is low 13's and then straight to 15's soon as i hit 3500rpm in every gear and i lift...The car starts right up and runs perfect and is in the normal 14.7 area while cruising and idle. I do feel a hesitation once i get up to 3500rpm area and it goes lean..I am basically looking for ideas...I have already cleaned the maf, I get the AAM adapter to test fuel pressure monday so that is my next step. I am guessing it is either a fuel pump problem and is not flowing the correct pressure or a clogged injector that is unable to keep up once it has to???? any other ideas? i feel if the maf sensor was bad it would act differently, also i dont hear any vacuum leaks while searching or exhaust leaks before the sensor..

open to ideas while i wait for my adapter to test fuel pressure before i tear the injectors out to test....

 

your thoughts are in the right direction, keep at it.. although i don't know what is normal a/f for a bolt on n/a car. Change the spark plugs would be my first step. Unless the your fuel is contaminated, it is highly unlikely it is a fuel pump/fuel screen issue

 

optimal is around 13.1 i beleive for n/a...15's is quite lean for wide open throttle, it will even go into the 16's if i hold it longer...My plugs are not old and not the problem, the car doesnt miss or skip or anything but does feel like is hesitates once i get to 3500rpm...also i have already ran through about 3-4 tanks since the issue started, its not the fuel..Im doubting its the fuel pump but i have seen in the past a fuel pump act this way and not flow the correct pressure while it was on its way out...My number 1 guess is a dirty or clogged injector

also no codes or cel from anything

 

low fuel pressure or volume.

 

^^i am hoping low fuel pressure, leading to weak fuel pump..easy fix..

i beleive from previous reading but not positive on what the fuel pressure should be..

51psi at idle? not positive on that or wide open throttle 52 psi wot?

 

for a while now my gas gauge has been messed up, at times will say i dont have gas when i do but has never made a difference in the way the car runs..Could that have anything to do with this? maybe the sensor in the tank or something is not sending gas or sensing there is gas, idk..? I will be testing fuel pressure later today after i get out of work..

still no check engine light or anything

 

Unfortunately there is not much information out there about the way the factory fuel system works. Yes, you should be about 51psi at idle. I've been having similar problems with a procharged 350 we have. Is it intermittent or just always falls apart around 3500?

 

It is always at 3500 rpm give or take in every gear, goes from low 13's straight to high 15's on the gauge once i get to 3500rpm, but then will return to high 14's by redline if i do hold it out...seems to feel worse at lower gears though as far as the holding back feeling once it gets to 3500rpm...

 

I've got a somewhat similar issue with this customer's car, although it goes rich and misfires around 3500 under load instead of going lean, then cleans up.

 

i tested fuel pressure today and it was a steady 52psi at idle and then under load was bouncing and wouldnt hold steady...it bounced around 48-49psi...thoughts?

fuel pump going bad?

 

sounds like it.

THe higher the rpm under load the more it will drop if it's bad and not supplying. That plays right into the symptom of a/f getting leaner and leaner as rpms get higher.

walbro is like 90$ so go for it.

also, on the stock system the fuel pressure doesn't rise. It should stay constant. If anythign it might come up slightly due to increased voltage over idle, but you would have to ask someone if it would even be enough to raise it 1psi. I don't think it would raise at all though.

 

^^ok but either way it should not drop at all correct?

 

I would think that it is going to drop some, injectors are firing more frequently and the pressure drop across the rails is going to be higher.

I've been down this road trying to diagnose the one I'm working on and the problem is that the info for these fuel systems just isn't there. On some of the later Ford and Mazda returnless systems the ECU ramps the voltage going to the pump to keep the pressure constant under load, other systems just compensate by increasing injector pulse width more.

I've been over the service manual again and again, the info just aint there.

In either case I don't think 2psi of fuel pressure should cause you to lean out to dangerous levels.

 

im losing 4psi of pressure, and yeah it doesnt seem like alot but i was told there should be no pressure drop from my tuner and that it should be very steady pressure and not bounce around and he recommended to change the pump first..i found a used oem pump with 5k miles on it for 45 bucks shipped so i figured id try it out and go from there and test the voltage to the pump at the same time...besides that idk, my only other guess is an injector being clogged still, but the little loss in fuel pressure gives me a little hope it might be the pump...fuel injected cars with electronic pumps are very sensitive to pressure drops from everything ive read and seen personally, i mean im not extremely lean but i am pretty lean..15's instead of 13's a/f, and i do have plenum spacer, test pipes, intake motordyne xyz nismo mid and tail section so i am gonna be a little more lean than i should be anyway on the factory tune...worth a shot to change out the pump, easy to do and narrows things down one further...ill let ya know how i make out

 

if you have 40psi, fuel pressure is not the cause of running lean, look elsewhere.

 

wait, so you saw a 4psi drop at what rpm and what load? if you're watching it then obviously you're not on the road and giving it hell. I'm going to guess as the a/f goes up the pressure drop becomes greater but you'll have to risk it to get that far.

If you had an injector that was clogged it would not cause a drop in pressure. That injector would be using LESS fuel so it would actually cause a backpressure on the system.

why don't you adjust your tuning? You removed all your fi stuff on there and i do'nt remember if you said you had it retuned or not.

 

why do you say that, the car should hold pressure under load and not drop? if there is pressure drop then that would cause a lean problem, thats a fact, have u tested this personally? where else to look?...

 

It drops as soon as i go wide open to 48psi from 52psi and is not steady, it bounces slightly up and down 48-49psi, i had a friend in the passenger seat holding the gauge, it is steady 52psi until i go wide open...he saw it and i saw it, the car is back to n/a bolt on just on the factory tune it came stock with there is no aftermarket ems in the car..

 

can u explain this a little more...does that mean that the pressure would rise if it were a clogged injector?

 

also remember there are no codes, or misfires or anything