Take the 2-minute tour ×
Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It's 100% free, no registration required.

My 80,000 mile 2.0TFSI Turbo Audi has lost a lot of performance but no check-engine-light (CEL) or codes. One month ago an independent garage looked at it and did $2200 of work including transmission fluid, air and fuel filters, new sparks etc...

When I got it back it was fixed, and boosting with a healthy sssh on acceleration from 2200 RPM, which lasted for about 6 days and then suddenly back to poor performance or worse, and no noise from the turbo except at 6000 when high pitched whistle/whine evident. Fuel economy seems really bad - about 15MPG.

Took it back to garage for smoke test, vac test etc. no CEL or codes. They say it's boosting at 7psi, but that they feel a lack in performance. I guess they used a physical gauge, but I don't know how or where they took that reading.


I got a PLX kiwi and dashcommander, and am trying to find a holy grail in the numbers. I don't know how to use this stuff.

I can't read Manifold Absolute Pressure (MAP), sadly, because I suspect a leak. Don't know if it's missing, broken, not in this model car or what. update vag-com reads it fine, must be a problem with my software.

The right hand curve below is me accelerating from 10 to 45 in 10 seconds, throttle mostly open, then foot off the accelerator. I max out at 4870rpm and 20lb! of (dashcommand estimated) boost and lambda hits .7, HP hits 97. It's supposed to be a 200 hp car :-(.

graph of two burst of acceleration - I'm describing the second

Fuel trim Long term is +5%. I don't understand how that tallies with .7 lambda. Driver information system indicates fuel economy is about 15mpg.

I don't know about cars, but turbo working, fuel trim adjusting for lean burn, good MAF... Suggests the turbo is firing up, but somehow not resulting in engine power.


Recent services: I had 2 coil packs replaced about 4-6 months ago, may be unrelated to this fault. I have not replaced the timing belt. Brakes and tires all replaced 3 months ago.


What do people suggest to fix and or diagnose? Don't want to replace the turbo if it's just a leak.

Can charge air sensor tell me a MAP that might show air leaks between the MAF and the manifold? (answer - that's the right sensor)

share|improve this question
    
sorry about the poor visibility on the graph, the tool I use makes them like this. –  Alex Brown Mar 18 '12 at 22:45
add comment

2 Answers

I wouldn't rule out a bad MAF so quickly - there was a generation of VW and AUDI MAFs that slowly went south without any indication from the ECU that they were doing so and IIRC the ECU managed to compensate for the dying MAF for a while.

Also, if the ECU thinks you might be boosting at 15psi and using a conventional gauge suggests you're boost 7psi, you either have a massive boost leak or a duff sensor.

The fact that the fuel trim it +5 (what unit is that, percent?) and not negative suggests to me that you get more air into the engine than is accounted for and the ECU is adding fuel to get the fuel ratio back to stoich.

For starters I'd pull the plugs and check if they look like the engine is running rich, lean or normal. That should give you at least a basic idea if the problem is upstream or downstream of the engine. Basically the idea is that if the plugs look like the engine is running really rich, you might have a problem with the O2 sensor(s), if they look like the engine is running normal there's a decent chance that the problem is upstream of the intake.

share|improve this answer
    
That's +5% trim. –  Alex Brown Mar 18 '12 at 17:33
    
What do I look for on the plugs? –  Alex Brown Mar 18 '12 at 17:36
1  
Check if the electrodes around the tips and down from the tips look sooty (mixture too rich) or if they're whiteish/tan. Here's a reasonable set of pictures to give you an idea what you're looking for: theultralightplace.com/sparkplugs.htm –  Timo Geusch Mar 18 '12 at 17:51
    
Thanks VERY much for the answer. I'll talk to my local garage and if it pans out I'll check this answer. In the mean-time I'm going to leave it open to other responders to chip in. –  Alex Brown Mar 19 '12 at 6:57
    
Problem solved. Thanks very much for your input, although the MAF turned out not to be the problem. –  Alex Brown Mar 20 '12 at 4:43
add comment
up vote 1 down vote accepted

Problem solved : sticking valve in turbo

After running a solenoid check at the independent mechanics - which toggles the solenoids for as long as you like, I get power and turbo back with a vengeance.

This means the problem is with a sticking solenoid in one of the turbo valves - either the wastegate or the diverter valves. The mechanic mentioned as we were running the test that this often unsticks solenoids, so I asked him to let it keep clicking for a whole minute.

Neither of these is very expensive. Now I'm just going to wait until it fails again, and get it replaced.

The diverter valve was replaced by audi less than a year ago, so will still be under warranty, and given that I was getting boost (MAF records lots of air going in) I think that's the most likely candidate.

share|improve this answer
    
Took to audi who said that wasn't the problem, and charged me lots of labor and parts to find out. I think they are wrong, and the car isn't boosting again. –  Alex Brown Mar 29 '12 at 19:46
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.