[s-cars] UrS4 running Lean fuel mixture

Dave Tremblay da_trem at hotmail.com
Fri Feb 13 07:20:35 PST 2009

Hmmm, interesthing i'll check the M5 forum..
Pump is seeing 13.5+ volts all the time(its relayed to the battery)
Injectors are still the stock ones and they have quite a alot of mileage.
I need to do a pressure test to see what the walbro unit feeds to the motor...i dont know if its me but the whining from the pump seems louder than before..i'll do the pressure test!
I've just tested another wideband sensor and it hasent changed a bit.
Until thats fixed,i'll stay off boost!!

Date: Fri, 13 Feb 2009 05:29:12 -0800From: mikellardizabal at yahoo.comSubject: Re: [s-cars] UrS4 running Lean fuel mixtureTo: s-car-list at audifans.com; da_trem at hotmail.com

Interestingly enough, there's a discussion thread in the BMW M5 forum about MAF's going bad.Although the Bosch Maf in the e34 M5 & Porsche 928,911's of the 90's are similar to the UrS4, its not the same unit, but the metering is similar.When the Bosch MAF goes south,usually attributed to age, it loses the ability to maintain the voltage needed to send the ECU the right  signals.,thus allowing the car to run very rich at idle and around town driving. Once at the 5-7500 rpm range a bad MAF can go dangerously lean. One guy put a hole right through his M5's block. So its kinda odd that you're just lean all the time.Hmmm...Couple of things to check:Battery voltage :Voltage from idle to load. ( You need at least 14+ volts @ WOT IIRC ) The Walbro might be voltage starved giving impeded flow.Stick a FP gauge before the rail.Make sure you've got at least 4 bar.Injectors ? a bad batch of dirty gas can really do a number on flow rate. FWIW- You're running scary lean at boost. I'd keep the revs under 5K for now.Walbro's are a hit & miss FP. Q control is moderate at best. Ask the Subie guys.Good luck.

More information about the S-CAR-List mailing list