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Old Thu, Apr-13-2017, 05:55:03 PM   #1
cpandrewschmidt
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Default rich condition and fuel pressure help

Hi all,
I have a 98 M3 with a Eurosport supercharger recently acquired and I have been doing maintenance. I'm chasing the P1108, 1109 CELs. Done just about everything in the book I can think of, vacuum leaks, new o2 sensors, ICV cleaning, vanos kit, valve cover, fuel filter, CCV, clean MAF. I'm running rich with fuel trims of LTFT -8.6% and STFT -20% ish at 2500 RPM.

I checked fuel pressure. With ignition on car not running I get 41 psi with FPR vacuum line plugged in. However, its pressure starts to drop off quickly. Like 30 psi within a minute. With car running FRP vacuum line in I'm at 41 psi and 51 psi with it off. So, I believe that's OK. Appears FPR is working then? So, I think injectors might be leaking. Unplugged injectors, turned on fuel pump watched injectors, no leaking.....but pressure still drops. So, car runs steady at 51 psi with FRP unplugged, 41 psi with it plugged in. When I start the pump FPR plugged in (not starting the car) the gauge instantly goes to 51, but immediately drops to 41 psi then pressure bleeds off somewhat quickly.

I started the car and turned it all the way off and pressure holds, doesn't drop off. That tells me it doesn't appear to be siphoning back when car is off, I've never had a hard start problem so it's not a check valve. Pressure only drops when key is in AUX position. When I pinched the fuel lines at the back of the rail the pressure on the gauge would go up and down, doubt that means anything.

So, still maybe a partially functioning FPR if there's such a thing? Hate to throw $90 at one not truly knowing. Or maybe it is tune related, but this problem didn't exist when i first got the car. I'm out of ideas. I took to a shop who could dig deeper with their code reader and he claimed if it weren't for the supercharger the car is running within BMW stock specs. He claimed it's probably the tune. I checked with TRM tuning who did the car and they said their specs would have the fuel trims targeted at 0%. So, I still think it's mechanically related.

Thanks for any tips you might have!
Andrew
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98 M3 Eurosport SC sedan
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