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Title: diagnosing possible maf sensor fault Post by: slopster on June 23, 2014, 07:10:29 AM Car is not making the power it should and I suspect the maf sensor for following reasons. Anyone think I'm right/wrong/way off the mark - before I fork out for a new one. Car is A6 c5 4.2 with 6mt conversion. This issue was present before the conversion and ever since I've owned it.
1. Logged in vcds it I'm getting maximum 152g/s. Logged during 30-90mph roll ons in 4th gear. 152 seems a bit low when I hear it should equal 80% of expected power output (240g/s for 300hp) but not sure if thats a hard and fast rule. 2. When I accelerate from a standstill it pulls nicely for about a second then feels like a 2 litre engine thereafter (I was thinking the ecu is making enrichments for the rapidly opening throttle and then when it gets a solid maf reading it switches to that only the maf reading is low). 3. It idles smoothly but sometimes takes a while to settle when you put the clutch in suddenly. 4. Unplugging maf seems to have no effect (This is not what I expected) So do you reckon maf or something else. These issues occur with both the original .bin and the manual 559d one I've been playing with. Title: Re: diagnosing possible maf sensor fault Post by: slopster on June 23, 2014, 07:20:50 AM attached csv log
Title: Re: diagnosing possible maf sensor fault Post by: tjwasiak on June 23, 2014, 07:26:23 AM You should log your lambda voltage - even if you are running narrowband sensor it should show lean mixture if MAF is so low.
EDIT: You should rev it too limiter as it could be right to measure ~150g/s @~4k RPM! Title: Re: diagnosing possible maf sensor fault Post by: nyet on June 23, 2014, 08:59:52 AM maybe intake leak?
Title: Re: diagnosing possible maf sensor fault Post by: ddillenger on June 23, 2014, 09:03:12 AM Here is a log of a 2001 A6 4.2. 220g/s.
Title: Re: diagnosing possible maf sensor fault Post by: tjwasiak on June 23, 2014, 09:07:42 AM After quick comparision slopster's car is not showing small airflow as in ddilenger's log it is also reading ~150g/s @~4k RPM.
Title: Re: diagnosing possible maf sensor fault Post by: ddillenger on June 23, 2014, 09:12:01 AM After quick comparision slopster's car is not showing small airflow as in ddilenger's log it is also reading ~150g/s @~4k RPM. Check your intake manifold flaps. Chances are they're broken or stuck, and that will cause what you are experiencing. Title: Re: diagnosing possible maf sensor fault Post by: slopster on June 23, 2014, 09:13:49 AM maybe intake leak? That was my first thought but couldn't find anything. I'm guessing a small leak would only affect low speed running and a big leak would be blatently obvious.Title: Re: diagnosing possible maf sensor fault Post by: slopster on June 23, 2014, 09:19:05 AM Check your intake manifold flaps. Chances are they're broken or stuck, and that will cause what you are experiencing. Ah yes I should have mentioned this - they are broken (as in someone has tried to unstick them and snapped them) but do they really make that much difference. I reckon I'm only making 2/3 powerTitle: Re: diagnosing possible maf sensor fault Post by: ddillenger on June 23, 2014, 09:21:55 AM Ah yes I should have mentioned this - they are broken (as in someone has tried to unstick them and snapped them) but do they really make that much difference. I reckon I'm only making 2/3 power Yes. You will lose 40hp in the midrange and more on top with them broken (depending on which way they are stuck). Title: Re: diagnosing possible maf sensor fault Post by: slopster on June 23, 2014, 09:28:59 AM Wow I thought they'd only made 5 -10hp difference. I'll have to look at removing them or getting them to the mid range position. Or Finding another manifold
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