MyE28.com

Okay, so a while ago I was on here trying to figure out my so called fuel issue. Todd suggested that I hook up a fuel pressure gauge to see what was happeneing under boost. I did that, and found out that my fuel pressure doesn't drop under load, nor boost. It actually increases like it is supposed to. Now im really confused. It seems that my lean out symptoms occur when im at partial (cruising) throttle for a while and then decide to punch it. If I try to do that, my a/f meter reads red (lean) and I have to get out of it. Yet, the fuel pressure stays the same. The only time I can really floor the car is after it has been idling for about a minute. My fuel pressure readings are at 45 psi at idle or no throttle, and 50 psi under boost/load. Additionally for the first few seconds of full throttle, regardless of going lean or not, the Fuel pressure psi fluctuates between 50 and 40 very rapidly. This seems to happen for longer and have a greater fluctuation when it decideds to go lean. The only things I could think of now are my injectors (TCD 30 lb/hr) or my chip (TCD as well). Todd, I'm looking at you for some advice or help. Please! It's annoying not being able to do highway pulls.

I'm not an expert, so this is a shot in the dark.

How old is your fuel filter?

That was removed completely to eliminate a possibility. I have the 255lph walboro intank pump, in addition to an external pump.

Did you remove the fuel pressure dampener installed inline before you get to the fuel rail. I removed mine and installed a gauge in place and the gauge seemed to bounce around a lot, but i resintalled the dampener and it seemed to get the bouncing around fuel problem fixed.

Im guessing since you are running a chip and larger injectors you are running the 059 535i ecu.

Have you done any tuning of the AFM to help eliminate or pinpoint the problem. Why did you remove the fuel filter? Its not the restriction problem and I think it should go back to help filter the fuel and eliminate other problem occuring while you are finding the problem.

Good luck.

have u tried using a WOT switch under boost?
had similar problems on turbo e34.
also, 50psi fuel pressure isnt going to make a difference under boost. i'd try closing the adjustmanet knob full, and try to get the fuel pressure at least to 70 psi under boost.

What is this fuel pressure dampner? I dont remember ever having one installed on my car. I removed the inline fuel filter because I have a very good intank one installed, although I plan on installing a high flow filter inline soon to replace the old one. Also, I have heard of that WOT switch, how does it work/how is it installed? I'd like to do that because I hate being lean under partial throttle even if it isnt really hurting anything. Also, I'm wondering if it could possibly be an injector issue, because a little while ago I pulled the plugs, and cylinder 4 was very rich, while cylinder 3 was very lean. Also, I really dont think it has much to do with puel pressure, because when the car seems to run rich, and when it runs lean it has the same fuel pressure. Therefore, I doubt more pressure would affect it much, although i can check.

WOT switch, used mainly on water injection systems, is just an adjustable air pressure switch that either opens or closes when it hits the set pressure.
since our cars use a TPS switch to go from the regular fuel map to the wide open map, when the throttle is wide open.

you install this boost switch parralel to the WOT switch, so it bypasses the circuit.
therefore the ECM goes into the WOT map when the car gets to 1 or 2 psi , rather than when the throttle is wide open

Papa,
While your solution of tricking the car to be WOT at part throttle may work, its not a solution I like. WOT map is just that, a WOT map where the air flow is high enough to make that map work.

Anyway, if the fuel pressure is ocsillating between 40-50psi, thats part of your problem. This shouldn't happen. Under bootst the fule pressure should be stable and rising with boost. It should get to your higher pressures as soon as you start runing boost. You need to adjust(tune) your FMU better or It may be faulty?

If you have differences in cylinder fuel richness, your inj's may be an issue. You may need to get them cleaned and flow tested. There are many places that do this.

RussC

Yeah, I have a crappy fmu from bav auto (I believe). It does not have the capabilities to increase rate of rise under boost. Because I am a poor high school student, im saving up for a cartech one. I think its a good idea to get those injectors flow tested. Any ideas why my injectors would be faulty? I got them around a year ago. Thanks for the info!

If your not runing a true FMU, your going to have problems.

The biggest issue is clogged inj's. If they sit around with old fuel in them, they will gum up and clog and hence need to be cleaned and flow tested.

RussC