Hi, I have a very curious fault on a car that came to me today. ABF mk2 seat that runs until hot then misfires, backfires and dies. Leave it a couple of minutes and it fires up on the button. It had been in a garage that diagnosed the dizzy as being faulty so that was replaced by a new bosch unit along with rotor, cap and leads. Crank sensor was also replaced along with a coil pack. I tested the coolant temp sensor and that was finished so replaced that. The plugs were also replaced as they were totally finished. I swapped out fuel pump relay and ECU relay as a matter of course for known working ones. Throttle body was pretty filthy so that was removed and cleaned properly, potentiometer was also checked for free movement. So, car starts from cold, runs sweet as a nut, temp needle sits at 12 oclock and idle settles to approx 900 rpm. Oil temp increases to 82 degrees after about 10 mins. The car begins to run lumpy and at this point, if you press the throttle it reaches about 1500 rpm and then the revs just pulse regularly. Then it misfires, backfires a lot and dies. ISV clicks into life and operates as you would expect. No codes found on VCDS Lite. Does the same with Lambda unplugged. I have a spare lambda but I really doubt it will solve the problem, will swap it out anyway to be thorough. What I have not done yet is continuity check the ecu loom. I am wondering about itbeing an ecu fault. It's like it is dumping unburned fuel into the exhaust manifold.. overfueling or losing spark is unknown yet. All plugs fire sequentially witha decent spark. Any advice would be greatly appreciated guys Cheers Stu
Yeah I have had many issues with them in the past, 3 spares have now been tried, including a known working one from my own car.
The owner reminded me that the ECU had been chipped some time ago.. it had also had a u281 diagnostic reader plugged into it while the ignition was on just before this issue arose. I know they are a cheap reader but I havnt heard of any issues with them??
Talking to the owner a bit more about it, he said it didnt seem to fit right and had to hold it in quite hard. I am thinking that the ecu could well be the issue as it religeously starts from cold and once it gets up to temp it's like the ignition timing screws up and misfires dumping fuel out of the exhaust valves causing loud backfires. Possible the warm running variables are corrupt? Get it started again and it runs for tops 2 minutes before doing it again.
I would look in the area of the hall sender / distributor - when the seals start to break down it can cause all sorts of running issues, including the ones you mentioned above - cutting out, kangarooing, pops, bangs etc. As if you had put the HT leads on incorrectly. I had this issue on an 8v Golf - ok it is a different engine, but the same can still apply. Took me ages to track down, changing so many needless parts in the process till I came to this. It also only did it once the engine was warm, whether this is because the oil was hotter and runnier, so could squeeze through degraded seals, I'm not sure. Worth a shot
Cheers Dennis, there are so many red herrings with this car it's unreal. Fuel pump was running constantly the other day and then it packed up after getting very hot.. motor wouldnt run in it even with an artificial feed. Replaced it for a worker.. still misfires and dies when hot. The dizzy is a totally new bosch unit so should be ok. ECU was ruled out once it was tested with a known worker. Not getting to spend much time on it just now but the whole loom is being tested for shorts/breaks on saturday.
Hi mate, Did you fix it yet? I am having similar problems on my MK2 Scirocco with ABF fitted. When it gets hot it would run roughly then die. If I press the gas pedal down it would start running even more roughly... and will eventually die... Any ideas? Cheers, Tom
