Knowlegeable D3 mechanic/garage needed?

centurion · #1 22nd June 2015, 03:58 PM

afternoon,

I have this very weird issue with my car that I have taken to several reputable places to date and they haven't been in position to diagnose or provide a 'fix'... hence was wondering if this is something you could advise on and recommend someone who actually knows D3 A8's and especially 4.2TDI motor?

Issue:
cold - working fine;
temp slightly up: starts stuttering/juddering at low revs
nominal working temp.: all fine again

to date I have replaced MAF's, air filters with genuine Audi, checked VCDS several times to no avail.
MAF's were replaced due to similar symptoms I had on an A6 2.7T when it failed.

something to note that A8 worked brilliantly when MAF's were off [Check Engine light came on but there were no juddering at any point and I have driven it for a week like that]. Thinking MAF's were erroneous I ordered new Denso parts (x2)- replaced them and the issue reappeared so to speak. I also ran several scans on VCDS w/o anything tangible that could point to the malfunction.

and to add... I had driven the car around Europe like this [with 'an issue'] there were no problems having covered 4.5k miles apart from what I described earlier. I must say that I did 155mph on several occasions and having brushed off several 911's en route

I don't think that car has a major problem... it must be something electrical that controls fuel-to-air mix etc.

I'm not perfectionist by any means but this had been bugging me and I'd really appreciate need someone who understands these beasts to diagnose the fault hence the pleas for assistance

?

any advise would be appreciated... thanks.

carmel120 · #2 22nd June 2015, 04:30 PM

hi have you tried a remap.

cheers trev

snapdragon · #3 22nd June 2015, 05:40 PM

Hmmm, during warmup the bypass on the fuel filter head will close. Maybe worth checking the seal on that or reading up on it.
What about EGR flow actual vs specified in VCDS? If you use the graphing feature and advanced measuring blocks do they correlate? EGR can use lambda probe after exhaust manifold or air mass to feedback it's flow.

Turbo Tony · #4 22nd June 2015, 07:01 PM

My Volvo had a similar issue and it turned out to be the engine temp sensor.

Normally, it would produce a fault code, but maybe it's only misreading slightly at certain temps?

Adrian E · #5 22nd June 2015, 07:24 PM

Apols if I've missed it, but can't see a location in your post for a recommendation?

Johnmed · #6 23rd June 2015, 09:38 PM

Yeah we need your location mate.

centurion · #7 24th June 2015, 09:25 AM

Quote:

Originally Posted by snapdragon

Hmmm, during warmup the bypass on the fuel filter head will close. Maybe worth checking the seal on that or reading up on it.
What about EGR flow actual vs specified in VCDS? If you use the graphing feature and advanced measuring blocks do they correlate? EGR can use lambda probe after exhaust manifold or air mass to feedback it's flow.

I will do another run tomorrow night... in the meantime will you be in position to share with us what needs to be done [and How pls

]?

centurion · #8 24th June 2015, 09:26 AM

I'm based in London and travelling is not an issue for a right mechanic

.

Thanks

ainarssems · #9 24th June 2015, 10:49 AM

I second other member views about temp sensor an EGR valve. Temp sensors are known to go on VAG cars and are cheap enough to do as preventative maintenance or part of troubleshooting, not sure how easy access is on 4.2TDI.
Another cheap thing to do not mentioned yet is fuel filter and making sure all the fuel line joints are sealed properly and not leaking. After that you are getting in more expensive territory like injectors, but needs more investigation, looking at measuring blocks etc on VCDS.

Unfortunately cannot recommend any garage as I am not near London and I do pretty much all work on my cars myself anyway.

Johnmed · #10 24th June 2015, 11:04 AM

Quote:

Originally Posted by ainarssems

I second other member views about temp sensor an EGR valve. Temp sensors are known to go on VAG cars and are cheap enough to do as preventative maintenance or part of troubleshooting, not sure how easy access is on 4.2TDI.
Another cheap thing to do not mentioned yet is fuel filter and making sure all the fuel line joints are sealed properly and not leaking. After that you are getting in more expensive territory like injectors, but needs more investigation, looking at measuring blocks etc on VCDS.

Unfortunately cannot recommend any garage as I am not near London and I do pretty much all work on my cars myself anyway.

I concur about temp sensors. Not saying it may be your culprit, but they're cheap and easy enough to change, depending on location.