90' V8Q surging under acceleration...
04-21-2009, 12:01 AM
#11
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someone refresh my memory on where the fuel pressure regulator is? is it that little easy to replace box on top with the two allen wrench bolts and the fuel line going to it? fairly cheap? about 80 bucks or so? be nice to me im on pain meds 
09-07-2009, 12:01 AM
#13
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I have the same issue under acceleration. Only it's quite faint on normal driving. So why do you guys think it's ISV causing the problem? It's not even being used when driving, only when the car is idling.. I checked mine but it's rotating quite easilly so i don't think it's the problem.
Next i was going to check the fuel pressure, so i can see if it's the FPR doing the problem. Hard to find the proper connector to tap into the fuel line, since the thread is weird like 14x1,5 i think.. :/
Next i was going to check the fuel pressure, so i can see if it's the FPR doing the problem. Hard to find the proper connector to tap into the fuel line, since the thread is weird like 14x1,5 i think.. :/
09-07-2009, 04:43 PM
#14
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The ISV allows air to bypass the intake. If it's not functioning properly, it may cause inappropriate air/fuel mixing even beyond the time the engine is at idle. So it could cause uneven acceleration. I recall postings on the audifans V8 list to the effect the fuel pressure regulator has a "life span" between 30k and 40k or so miles, after which it can develop variable behavior.
09-22-2009, 01:39 AM
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I replaced the O2 but that did have little to no effect. But i noticed my fpr was leaking to the return line when engine not running, so i suspect that could be the problem. At least replacing that should fix the long cold starts i've been having.
10-25-2009, 05:26 AM
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A little update, i found that when i unplugged the O2 sensor the pulsation seemed to disappear. But the O2 was brand new so i suspect there is something else wrong with the fuel mixture and the O2 is trying to compensate-hence the pulsation..?
But, i have already recently replace fuel pump/fpr and havent found any vacuum leaks, so i guess there is not much other thing to check than the injectors?
But, i have already recently replace fuel pump/fpr and havent found any vacuum leaks, so i guess there is not much other thing to check than the injectors?
10-25-2009, 11:39 PM
#17
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Unplug your ISV? I put a new ISV in mine and it started to do this..had to use the old one which was properly sealed (and broken).... oculd have simply done a direct connect to remove the ISV from the loop. ONly issue is typically cold starts (requires some throttle) but once a bit warm all is well...not fixing that any time soon.
i had the same problem though with my automatic v8 even after changing the o2 fpr and cleaning out and replacing the ISV and MAF. was getting terrible gas milage too. 13mpg. Surging usually went away after a few miles and warming up. never did figure it out. I suggest maybe trying to get a hold of or barrow a VAG-COM.
Last edited by Calbha; 10-25-2009 at 11:42 PM.
10-26-2009, 12:59 AM
#18
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I thought 13mpg is normal for an automatic V8? 
In my case, vag-com doesn't help too much since there are no fault codes and it's not able to monitor live-data on these old control units..
In my case, vag-com doesn't help too much since there are no fault codes and it's not able to monitor live-data on these old control units..
10-27-2009, 07:24 AM
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