[s-cars] UrS4 running Lean fuel mixture

[Mark Strangways]

This just came to mind,
At some point the ecu goes from closed loop to open loop during boost.  
At this point the MAF would be used alone (with out the O2 sensor) to  
set the injector duty cycle.

Try unplugging the maf and see if there is a change, with out MAF I  
believe the ECU will go to its tables for the injector rate.

Mark
On 13-Feb-09, at 2:54 PM, Dave Tremblay wrote:

>
>
> I just swapped the fuel pump with a good oem unit. Same damn result!  
> At this point i'm really suspecting a bad maf..everything fuel-wise  
> as been changed.
>
> Next week i'll try another maf(RS2). Until then, i will continue  
> searching the problem.
>
>
>> From: blade.dawn at mac.com> Subject: Re: [s-cars] UrS4 running Lean  
>> fuel mixture> Date: Fri, 13 Feb 2009 11:29:25 -0500> To: da_trem at hotmail.com 
>> > > Dave,> > Do the volume test, it's more critical, even a weak  
>> pump will > build up pressure eventually. Call if you need  
>> details.> > Bruce Everett 574-935-4767> On Feb 13, 2009, at 10:20  
>> AM, Dave Tremblay wrote:> > >> > 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.> >  
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