86graphitecoupegt

On Friday the CGT just started really losing power and stumbling after driving for 15 or so minutes. I was able to drive at 10 to 12 mph to park it. On Saturday, it started after turning it over for a while while playing with the throttle and then the revs came back up and I was able to drive for 10 minutes when it stumbled back to a crawl again. I had it towed to my local garage where they put a new fuel filter in - which apparently didn't help. This morning I started it again by playing with the throttle and drove home - after letting it idle for a while. I drove around the block a few times and then it stumbled back to a crawl again and a I drove home at 5 mph and parked it. I should mention that just prior to all of this I put some gas in it because the light went on on the gauge - which was why I first thought of dirt in a fuel line. I should also mention that when I was driving it home at normal speed (prior to stumble) it did feel like it didn't have all the usual power. Any ideas anyone?

Max'sCoupeGT

I had this problem on a 5000S I was driving. All of the rust/gunk from inside the tank settled on the screen right above the pump. The car would try to suck fuel through the screen and all of the rust would get in the way. Toss the car around a little or stop it and start it up again, the symptoms would disappear. I'll bet if you pulled the tank, you might find a little suprise. Luckily, resealing the tank is no big deal and pretty easy.

AudiSport4000

The Coupe GT's with the digi dash have a low gas light? I was unaware of this!

Does it feel like the car is just losing power?
Car start up fine and runs fine for 10-15 minutes?

86graphitecoupegt

The car seems to have power at first but doesn't really accelerate - and then when it goes zip it just drops to no power - I just play with the gas pedal to settle to a rough idle and drive in first at 5 to 10 mph.

Actually the light story is a whole different story - because the digi-dash lights haven't worked for months. They went on and I could see the trip computer miles remaining lights, showing I'd better pull in quick.

But what is wierd is that the digi dash lights are all working at the moment ever since Friday night! There I think I have a ground or other wire connection issue to lighting circuit on the circuit board in the dash. I can see that the dash is still working sometimes when outside light is shining on the dash at just the right angle, so I know that it's just the lights (all 3 are either on or off) at the same time). And I can't find anyone that works on those digital dashes - but like I said that's a whole different story.

AudiSport4000

I didnt know if there was an actual "gas idiot light" on the CGT digital cluster or not.

DavidHH

Fuel System
While it could be dirty gas, and a bottle of techtron would help break the dirt down, it might just make it worse by loosening up the crud.
[I have used techtron for the last ten years and have not replaced any fuel system parts on our cars except the vanagon westy's fuel filters that crack at high altitude.]

Electronic
When you diagnose the problem, keep in mind that the wiring was barely adequate when audi built the car, and it's ability to conduct electricity has only been getting worse over the years.

I would my fluke multi meter with a clamp on AMP meter,
to check the current to the fuel pump, the distributor, computer, etc.

You can easily make a blade fuse and fuse holder into a test loop so that you can see if anyone is being starved of current by overheated wiring.
As it heats up the current flow will decrease, it will also melt insulation, relays, etc. in a way that may still pass a continuity test.

[you want to replace this]
---fuse---

[with this]
--+ +--
| |
| clamp on meter or
| standard auto amp meter gauge
| |
+fuse+

Happy hunting,
David

Katman

IF the o2 sensor goes really 'bad', you could get similar symptoms.

But for it to be the o2 sensor, the problem should ONLY show up if you are starting out with a cold motor, and the symptoms will go away once the motor is cold again.

How that works:
ECU doesn't look at the o2 sensor, until the coolant temp sensor tells the ECU that the motor is warm. So.. If you have a bad o2 sensor, it won't show up until the ecu goes to use it, and that only happens after driving it a bit.

Easy to test the theory though: Undo the o2 sensor (Sort of below the distributor, near the heater valve). Actual o2 sensor connects to a odd black boot, on the end of a thickish green wire going into the wiring harness.

Disconnecting the o2 sensor makes the ECU go into open loop mode, using it's default mixture setting.

Or..

Strap the full throttle switch on the top of the throttle body closed (with a tie wrap or similar)

Full throttle (where you click the switch on the top of the intake) also overides the o2 sensor, so if the motor works ok at full throttle, another clue to problem being the 02 sensor. (although a bit of a pain, driving full throttle or nothing!)

Jretal

my solution was to yank the motor and install the turbo motor/EFI/034 :-P

BUT, I believe it was caused by bad ECU grounds... might want to check those and see how they're looking.

My 4000 would sometimes start, and othertimes just kinda stumble over itself when it started. WHen it would work right it'd be fine, but then suddenly it would not rev over 4k rpm, even with the throttle to the floor.

WHen it's doing it, have you tried jerking the car left and right? Give it a try... if it comes back to life, it's a wire somewhere dealing with the CIS stuff or the grounds to the ECU.

86graphitecoupegt

Actually the fuel gauge symbol and fuel level indicator bar start to blink when there is only about 2 and half gallons left.