I got a 300 tt from '93 (originaly sold in Germany if that matters). Two weekends ago, we did some minor repairs on it. One of the things we wanted to do was to correct a problem with one of the front lights. This involved getting in to the front light unit and unless we did a lot more work than needed (it was the first time, so how knows), getting that unit out means taking of the front and some stuff behind it.

 

This seemed to work well, but when I took it out for a spinn, the engine died on me by a red light. No obvious cause so I had to get towed back home again. It seems only logical to start with the areas we touched when we did our repairs and the only engine related thing we touched was the air flow meter. Fiddeling a little with the connector seemed to magically solve the problem. Testing this a day later, the car started without a hitch. I left the engine running for 5-6 minutes, no problems. Tried to drive away, 50 meters later, the engine caughs twice and I have to be towed for the second time in three days. :(

 

The engine managed to run ones more for a short while, and now it won't start.

 

First we tried to run the self diagnostics of the ECU. Mode I reports that it is working correctly. Mode II - an utter failure. The diagnostic mode selector isn't there! There's no trace of it. Could it be placed somewhere else (not on the ECU) in my car, or did they make versions without it?

 

We've checked the different parts of the engine. There's gasoline in the clyinder and there's a spark on the spark plug but it doesn't ignite. The only thing that I can se missing would be air. Wich brings us back to the air flow meter. As I understand it, there's a fail safe system if the air flow meter should fail. If it fails, the car will still run but at a maximum of 2400 rev/minute so it doesn't sound like that's it.

 

I'm out of ideas. Any help will be apreceated.

Try disconnecting the airflow meter altogether, that may help if it's got a problem.

There is an easier way to do the ECU diags :- http://www.twinturbo.net/ttnetfaq/FAQpages/ECUdiagnostics.html

 

See how you get on, them come back with more questions

sounds more like the PTU.

 

Vijay

My AFM had an intermittent problem - it would just cut out totally - not do the 2500 revs thing - car wouldnt start and it was happening to me all the time - got so bad was gonna sell car - wish I would have tried disconnecting it to see if it would start and run at 2.5K - but I didnt. I think if it has probs it an cause your car to cut out.

I ran the diags on mine and it reported ok - buit died a week later again.

Replaced it and never had a problem since.

Thanks for the help and the good suggestions.

 

We tried disconecting the AFM the day after the first time the engine died, when we still could start the car again. Doing this made it impossible to start the engine, connecting the AFM made it work again. That's why we thought connector wan't properly mounted the first time.

 

I'm going to try the diagnostics tonight and see if it reports anything.

The self diagnostics first returned code 55 (everything is fine) but after attempting to start the engine, it returned code 21 (ignition circuit), pointing at the PTU. Indeed, testing it gave varying results if you tapped on it. Opening the PTU revealed that one of the connections to ground was broken. We'll see if we can fix it (soldering on heat sink is always fun) so that we can use the car until we can get a new one.

 

One strange thing though, whatever we did with the PTU, we could only give it no connection or make it behave with reversed polarity compared to this.

When you replace the PTU it would be advisable to go for the series 2 PTU...These are more reliable and have a lower failure rate ;)