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AudiDoc
AudiDoc, Independent Audi Shop Owner
Category: Audi
Satisfied Customers: 6426
Experience:  I've been working on Audis since I was 18 and own an independent Audi repair and performance shop
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Audi A6 Quattro: 2004 Audi A6 2.7T / hesitation while driving

Resolved Question:

2004 Audi A6 2.7T / hesitation while driving at 2000 rpms
Submitted: 1 year ago.
Category: Audi
Expert:  AudiDoc replied 1 year ago.
Hello, I'm Jason.
I will do my best to answer your question quickly and accurately using the information you have provided.

Ok, fuel trims are in spec. Got a few questions for you:

1) How many miles have you driven since shutting the check engine light off?
2) what codes were present before doing any repairs?
3) what tool/scanner are you using?
4) when was the last time plugs and coils were replaced, and what brand (this is important)
5) how did you check for air/intake/boost leaks, and did you check wastegate/boost solenoid hoses?
Customer: replied 1 year ago.

1 ) approximately 100 miles


2 ) 17965 charge pressure positive deviation / 17545 fuel trim bank 1 add / 17547 fuel trim bank 2 add / charge pressure faults gone after replacement of split intake boot / fuel trim within spec after replacement of MAF


3 ) VAG-COM


4 ) Plugs replaced last week with OE bosch


5 ) Pressure test on boost side / vacuum test for wastegates / tests ok


 


Now that engine parameters are within spec I am looking at transmission values. The shudder is consistently occuring around 1700 rpms. Torque convertor slip speed is inconsistent during the shudder until it is locked at higher speeds. Vehicle has 188,000 miles on it. Previously checked trans fluid level at correct operating temp and it was ok.

Expert:  AudiDoc replied 1 year ago.
Ok, great info back. Thanks for being detailed.

So, 100 miles should be plenty to get valid fuel trim numbers back. I assume all 4 are within +/- 3%? Considering you have vag-com, any chance you can grab a helper, so that I can walk you through a boost datalog?

Have you also checked both turbo diverter valves to see if they hold vacuum?

Ever see any P0741/17125 fault codes in engine or transmission controllers?
Customer: replied 1 year ago.

Between intake boot and MAF the fuel trim immediately came into spec.


at idle & partial. Operating within 1.8% to -.08% on all 4 values while driving.


 


I do have another set of hands


 


Bank 1 divertor valve is ok. Bank 2 divertor valve bleeds down slowly when vacuum is applied. I did not feel it was enough to effect engine performance.


 


No P0741 codes in ecm or tcm. No fault codes at all in tcm at any point.

Expert:  AudiDoc replied 1 year ago.
Ok, agreed on the diverter valve performance and possible affect.

Fuel trim percentages look great.

So let's do a couple of things with vag-com.
1) reset throttle adaptation. Key on, car not running, foot not near the throttle pedal. Go into engine electronics, basic settings, enter 060 in the group field, click go until field 4 reads ADP OK. If the car is an automatic, then enter 063 in the group number, click go, hold throttle to floor until field 4 reads ADP OK
2) then start the car, grab your helper, and find a stretch of road to do a complete 3rd gear wide open throttle pull from 2k to 6500 rpm. Select measuring blocks, group 115. Click the log button, find your stretch of road, click start, and go WOT through 3rd gear. Your helper will be able to watch fields 3 and 4 for requested VS actual boost. I'd like to know if the two numbers are more than 100mb away from each other. This will also show up in the datalog dump you can do into MS Excel once you get done.
Customer: replied 1 year ago.

I reset throttle adaptation


 


Specified vs actual values in channel 115 followed closely dependent upon engine load / max variance was 100 mb


 


Issue happens on light acceleration. Rpms flucuate by 200 - 300. Almost feels like engine is back firing or stumbling. Observed misfire recognition values. All zeros. Ignition coils appear to be ok visually. I would suspect a coil issue would demonstrate a misfire.


 


I am also using exxon premium fuel to rule out a fuel issue.

Expert:  AudiDoc replied 1 year ago.
Ok, good to hear about the 115 log.

And block 14-15-16 were clean.....
Agreed, if there was a coil problem, you'd see counters increasing.

This really sounds very wastegate-related. It would be interesting to get a mechanical boost gauge installed temporarily, since the sample rate on vag-com is so low...likely about 3 samples per second. Possibly an imbalance between the two turbos and the cracking pressure of each wastegate.
AudiDoc, Independent Audi Shop Owner
Category: Audi
Satisfied Customers: 6426
Experience: I've been working on Audis since I was 18 and own an independent Audi repair and performance shop
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