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Join Date: Nov 2009
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930 intermittent over fueling

Hi,
I have an 86 930 and it normally runs fine, but about once or twice a week it will start and run rough with a very very rich fuel mixture which will create smoke and it will produce very little power and be reluctant to increase RPM. Even when it warms up the problem continues.
Stopping and restarting the car doesn't help but the car will normally work fine again the next day. Both fuel pumps were replaced only a couple of years ago and I have checked the fuses and they are fine. Any ideas would be very helpful.

thanks,
Jay
Old 10-25-2011, 06:00 PM
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Have you checked the rear fuel pump relay...which provides power to the WUR heating element? Just because the fuses aren't blown doesn't necessarily mean power is getting to the pumps (has to go through the relays for that). Or, the next time it acts up, have a voltmeter in hand and pull the plug from the WUR and test for voltage. I bet you are seeing a loss of voltage and the WUR is reverting to cold-start mode. And/or, get your hands on the gauge setup for checking control pressures....connect it and test the control pressures when the car is running well...and leave it connected until the next time your car weirds out - then check the pressures at that time. Bet you would see low CP's.
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Last edited by mark houghton; 10-25-2011 at 06:14 PM..
Old 10-25-2011, 06:08 PM
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Thanks for your reply Mark, I thought the relay often stopped it starting and hadn't checked them as mine always starts up quickly. But I will definitely get the voltmeter when it occurs next time.
Thanks again
Old 10-26-2011, 01:39 PM
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Do you by chance have an O2 sensor hooked up in your car? I had a similar issue with mine, where it was smoking huge and burning so rich I barely got 60 miles to a tank. I changed the O2 sensor and that fixed the issue (although i run without one now).
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Old 11-09-2011, 01:29 PM
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Without known AFR's it can only be assumed that this is an enrichment issue.
If so there are a few things that control/affect the mixture:
> vacuum leaks
> WUR cold start circuit and warm up, electrical and mechanical
> system pressure (fuel pumps)
> fuel injectors
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Old 11-09-2011, 03:43 PM
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