My new purchase / science project
06-05-2007, 08:48 AM
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My new purchase / science project
Against all common sense and the advice of several people, I just bought a white 97 A8 yesterday - I had been looking at it for a couple of months and finally got it for a pretty decent price. Although it has a rebuilt transmission, it has some issues, the main one being that it appears that it needs a new Transmission Control Module (TCM). At least that's what the Denver Audi dealership has told the previous owner. It also seems to match behaviors indicative of a ECU that has/had moisture issues.
The two main symptoms are a multiple cylinder misfire that starts after driving it for about 15 min on the highway (temperature related?) and rapid cycling between 3rd and 4th (I think?) gear concurrent with the misfire. This is accompanied by a flashing CEL. The car runs/shifts like a top before this "event" happens. I posted the error codes previously.
I am having a hard time figuring out what the symptoms of a bad ECU vs a bad TCM would be. Could a faulty TCM cause rapid shifting between gears resulting in concurrent random misfires? Could a faulty ECU cause misfiring that would then result in rapid shifting errors? Could it be that BOTH units are fried? Could it be a wiring harness issue? Could it be something else entirely?
I think the best way to proceed is to buy/beg/borrow another TCM, follow the dealers diagnostic of a bad TCM and see if this is the problem. Replacing the ECU might be a second step? I have opened the electronics case by the firewall and inspected the ECU, fuses and TCM - they didn't look too bad, but it appeared like there was some water marks at the bottom of the case. There was some standing water under the cowl by the fender, but not in the box - easily fixed by pinching the drains free of debris. Plus there was a brass screw seat loose on the box body likely causing the seal not to seat.
I know I need to get a VAG-COM plus the diagnostic software - I'll order that in the next couple of days.
I'm trying not to drive it much until I've resolved the issue - but its hard to resist. What an incredible car!!! Elegant, refined, comfortable, athletic, easy on the eyes...
-Eric
The two main symptoms are a multiple cylinder misfire that starts after driving it for about 15 min on the highway (temperature related?) and rapid cycling between 3rd and 4th (I think?) gear concurrent with the misfire. This is accompanied by a flashing CEL. The car runs/shifts like a top before this "event" happens. I posted the error codes previously.
I am having a hard time figuring out what the symptoms of a bad ECU vs a bad TCM would be. Could a faulty TCM cause rapid shifting between gears resulting in concurrent random misfires? Could a faulty ECU cause misfiring that would then result in rapid shifting errors? Could it be that BOTH units are fried? Could it be a wiring harness issue? Could it be something else entirely?
I think the best way to proceed is to buy/beg/borrow another TCM, follow the dealers diagnostic of a bad TCM and see if this is the problem. Replacing the ECU might be a second step? I have opened the electronics case by the firewall and inspected the ECU, fuses and TCM - they didn't look too bad, but it appeared like there was some water marks at the bottom of the case. There was some standing water under the cowl by the fender, but not in the box - easily fixed by pinching the drains free of debris. Plus there was a brass screw seat loose on the box body likely causing the seal not to seat.
I know I need to get a VAG-COM plus the diagnostic software - I'll order that in the next couple of days.
I'm trying not to drive it much until I've resolved the issue - but its hard to resist. What an incredible car!!! Elegant, refined, comfortable, athletic, easy on the eyes...
-Eric
06-05-2007, 10:05 AM
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Re: Welcome fellow Coloradoan! Where- abouts are you located?
I'm up in Fort Collins (where I bought the car) but will be relocating down to NW Denver in July. Any other Colorado A8 owners on this site?
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06-06-2007, 05:28 AM
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We have had nearly the same Audi lineage...
My list includes a 4000Q, '91 200TQ, RS-2'd S4 and a highly modified urQ. Wifey had A4 & A6. Time to schedule a CO GTG soon...