Help me diagnose a P0171 fault
Discussion
https://youtu.be/llH9ec1a6MY
I'll understand if you don't have any interest in this whatsoever but thought it worth an ask.
2006 Kia magentis/Optima 2.0 4cyl 47k miles. Throws a P0171 code but only if take it for a good 20 mile run at motorway speeds. Once cleared it doesn't come back on unless do a similar journey.
Other symptoms include
- slight lumpy idle
- can sometimes take a bit longer to crank than you'd think, starts on about the 4th or 5th turn from cold, starts on the 1st when warm.
- revs holding a little high (1500) for several seconds before returning to normal idle speed.
To be fair it runs fine otherwise, pulls cleanly with no hesitation of loss of power right up to redline. Because of this I'm assuming the fuel pump is good.
So far changed spark plugs as needed doing anyway. Not had chance yet to check for vac leaks with a spray can of carb cleaner.
I'm suspicious of the upstream O2 sensor but not sure, does that trace in the video look suspect to you? I thought they were supposed to oscillate at idle? Other culprit might by a dodgy maf sensor, injector or a vac leak.
Amy pointers welcome.
I'll understand if you don't have any interest in this whatsoever but thought it worth an ask.
2006 Kia magentis/Optima 2.0 4cyl 47k miles. Throws a P0171 code but only if take it for a good 20 mile run at motorway speeds. Once cleared it doesn't come back on unless do a similar journey.
Other symptoms include
- slight lumpy idle
- can sometimes take a bit longer to crank than you'd think, starts on about the 4th or 5th turn from cold, starts on the 1st when warm.
- revs holding a little high (1500) for several seconds before returning to normal idle speed.
To be fair it runs fine otherwise, pulls cleanly with no hesitation of loss of power right up to redline. Because of this I'm assuming the fuel pump is good.
So far changed spark plugs as needed doing anyway. Not had chance yet to check for vac leaks with a spray can of carb cleaner.
I'm suspicious of the upstream O2 sensor but not sure, does that trace in the video look suspect to you? I thought they were supposed to oscillate at idle? Other culprit might by a dodgy maf sensor, injector or a vac leak.
Amy pointers welcome.
Judging by fuel trims i'd go with vac leak. Your fuel trim at idle is showing roughly 20% more fuel getting added to compensate for a lean situation, your trim shows an improvement at revs and comes down, because more fuel is naturally added which is now naturally compensating for the air leak.
At idle, a vac leak has a larger effect as there's little fuel going in.
At idle, a vac leak has a larger effect as there's little fuel going in.
Edited by robbocop33 on Thursday 17th January 08:58
Thrilling update!!
So I couldn't find a vac leak. But unplugging the MAF sensor smoother things out a treat. So got hold of one off a broken car etc voila...sorted.
Fuel trims now sitting at zero and smoothed everything out a treat.
Car is up on eBay now though as we happened upon a rather lovely BMW over the weekend and it's no longer needed.
So I couldn't find a vac leak. But unplugging the MAF sensor smoother things out a treat. So got hold of one off a broken car etc voila...sorted.
Fuel trims now sitting at zero and smoothed everything out a treat.
Car is up on eBay now though as we happened upon a rather lovely BMW over the weekend and it's no longer needed.
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