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Forced Induction Forum
Discuss supercharging, turbocharging and even nitrous and water injection here.

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Old 07-23-2013, 11:46 PM   #1
low flying
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Join Date: Jan 2012
Location: Santa Rosa, CA
Posts: 50
My Ride: 2003 M3
HPF Stage 1 going lean

From the first day that I tracked this car 2 years ago with stage 1 low boost, I have had a problem with the AFR going lean (above 11.5) starting at 6000 RPM WOT and getting to 12.5 at 8000rpm. The car only had about 67,000 miles 2 years ago and 75,000 now. I used 100 octane to keep the siren from going off. (I have never tried high boost so I have no idea if the problem carries over to high boost.)

Does the Walbro inline pump only come on during boost and at what point if that is the case?

Thanks to this forum, I was able to unlock the AEM and my tuner here at Sonoma Raceway was able to try to correct what John (at HPF) and I thought was a minor adjustment. John had tried once when I sent the AEM to him a year ago for a tweak. My new tuner said that I have either an injector problem or a fuel volume or pressure problem. All the plugs right after a hard track session look good with no varience. I'm inclined to think fuel delivery. We ran out of time today on the dyno to check fuel pressure. The car dynoed at 450 rwhp but I'm thinking it just isn't getting enough fuel. The problem has been consistant over the last two years so I'm inclined to believe that the in tank pump is working (and not getting worse) and the inline pump isn't.

I sure could use some ideas as how to proceed. I wish that we could have checked fuel pressure today. That seems to be the first thing to do but dyno time is hard to get locally and I have another track day coming soon.

So, again, when is the inline pump supposed to run and what switches it on if it isn't on all of the time?

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Old 07-24-2013, 12:12 AM   #2
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Join Date: Jun 2010
Location: Socal
Posts: 4,025
My Ride: 1000rwhp Turbo M3
Terry if the car isn't running right...fix it before you track it.

Fuel pump comes on during boost...not sure where it's set. Log into your AEM and familiarize yourself with the settings.
1000+RWHP, Lab22 Built Turbo S54 - BMW Half Mile Record Holder

Last edited by Commanderwiggin; 07-24-2013 at 12:12 AM.
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