Worrying electrical gremlin.....Help!

[NorrS2]

Folks


I am currently traveling 100miles round trip to work and there is a worrying intermittent issue with my ABY Avant! (i don't want to get stuck in the middle of nowhere!!!!)

This morning was the second time in the last week that at very light throttle cruising at 70 on the motorway (the previous occasion was at about 45 on B road) the car seem to completely "cut out" for a split second. The revs only droped by about 300 rpm and instantly resumed normal service. This was not a miss-fire on any given cylinder as you could feel the complete loss of ignition and backed up by the rev counter droping instantly.

My worry is that this is the start of something that could render me stranded at the side of the road. My confidence in making a journey is drastically reducing

Is this something that VAG-Com will pick up? i.e would that brief "fault" be picked up by ECU?

Has anyone else here experienced anything like this before?

Any suggestions GREATFULLY received .

Thanks folks

[dm80]

I'm no expert, but this was happening to me for a while. Eventually it would completely cut, and I'd have to stop by the side of the road. It would re-start eventually. Turns out it was a dodgy ECU. Replaced it (reluctantly) and I've had no probs since. Hopefully it won't be this for you and something simpler and cheaper, such as a dodgy sensor or whatever.

VAG-COM will probably point you in the right direction - you don't wanna see the dreaded 'checksum error' though!

[S2central.net]

Thats an odd one - I would check earth straps and the solidity of all the electrical connectors you can find in the engine bay - particularly those for the POS units.

Could also be a dicky fuel pump relay - hard to prove if the fault is intermittent, but buying a spare one of those is wise for anyone. Reminds me I need to get a spare one some time. Its one dopey cheap little relay that could have you stranded... Though of course you can hard-wire round it if you know what you are doing.

Paul

[NorrS2]

Thats an odd one - I would check earth straps and the solidity of all the electrical connectors you can find in the engine bay - particularly those for the POS units.

Could also be a dicky fuel pump relay - hard to prove if the fault is intermittent, but buying a spare one of those is wise for anyone. Reminds me I need to get a spare one some time. Its one dopey cheap little relay that could have you stranded... Though of course you can hard-wire round it if you know what you are doing.

Paul

POS Unit was replaced about 8 months ago, after the mechanic changing a Coil Pack tightened down the centre housing and squashed a coil pack wire at the bulk head side of the CH, which eventually shorted out one of the POS switches and blew the fuse for the ECU. Local stealer coudn't get a fault code from ECU but found blown fuse and traced back to coil pack wire shorting out. This is after replacing the other POS switch 3 weeks earlier when car was running on 4 pots.

I would have thought if there was a loose POS switch connection, the car would just miss-fire and lose a cylinder or two/three. This fault definately entailed a "complete" cut-out, however brief.

Spare Fuel Pump Relay is definately a good idea though Paul. Would that simulate a "total" cut-out?

Thanks for the responses so far

[S2central.net]

POS Unit was replaced about 8 months ago, after the mechanic changing a Coil Pack tightened down the centre housing and squashed a coil pack wire at the bulk head side of the CH, which eventually shorted out one of the POS switches and blew the fuse for the ECU. Local stealer coudn't get a fault code from ECU but found blown fuse and traced back to coil pack wire shorting out. This is after replacing the other POS switch 3 weeks earlier when car was running on 4 pots.

I would have thought if there was a loose POS switch connection, the car would just miss-fire and lose a cylinder or two/three. This fault definately entailed a "complete" cut-out, however brief.

Spare Fuel Pump Relay is definately a good idea though Paul. Would that simulate a "total" cut-out?

Thanks for the responses so far

I hope the butchery hasn't damaged your ECU...

But yes a fuel pump cutout would feel similar to this in my opinion.

[MidnightBlueS2]

AFAIK, it could be a cutting out MAF. Exact same symptoms on my previous BMW 530i V8 and a thorough cleaning of the MAF cured the problem... It also started happening when the weather got colder so there's maybe a correlation here...

[Graham]

Wouldnt a faulty Hall sensor cause it to do this aswell, if it was failing it would kill the rev counter and engine wouldnt it?

[S2central.net]

No - the CMP is a bit queer - if it fails while the engine is running, the ECU is clever enough to use crankshaft timing to keep going. However the engine will not start if CMP is dead.

Easy one to prove out if you like - just idle the engine and disconnect the CMP plug - it keeps running !

I'm talking ABY here - dunno if the 3B is as smart about hall sensor failure inside the dissy.


Paul

[Graham]

Ah Cool, well there is about an £80'ish guess saved. Cheers

[GT500]

I had this on a customers car, it was the ignition switch!!

Just change it, very cheap. white plastic thing.


Rob.

[NorrS2]

AFAIK, it could be a cutting out MAF. Exact same symptoms on my previous BMW 530i V8 and a thorough cleaning of the MAF cured the problem... It also started happening when the weather got colder so there's maybe a correlation here...

Ah!, the MAF, whilst the car is not consuming excessive fuel (as is did the last time I had to change the MAF about 50k ago) I am not getting the surge of torque I was getting a couple of months ago. Prior to getting the Timing Belt done 3 months ago I was also getting very intermittent boost cut-out, so I did the Mark H mod to ensure that the o'ring replaced 2 years prior was not leaking again. I have not had boost protection coming in since, so maybe that was the cause of that. As I say the low end torque has reduced which has propmted me to get the Isoprop**** stuff to clean the MAF as recomended previously on here. But would a MAF fault cause cut-out given there's no obvious fault given normal fuel consumption?????

@Paul

Although I didn't previously know (Hall Sender failure does not cause the car to cut out until restart), I believe Paul to be correct - when My Hall Sender failed 3 years ago, the car was running normally when I parked at work, but when I went to leave from work, the car would not start at all. It was diagnosed as the Hall Sender.

Fortunately, I have a spare ABY ECU although not Homefried . I would have thought, if the previous faults had damaged the ECU, it would have materialised before now, as the car has covered a good few K since then!

This is great guys, thanks for all the suggestions, I feel we are already grinding out the likely causes - keep it coming

[NorrS2]

I had this on a customers car, it was the ignition switch!!

Just change it, very cheap. white plastic thing.


Rob.

Was this an Audi / S2 ?

[GT500]

It was a 20v UR, I bet there the same.... not the lock barrel, just the switch its self..

[mcandmar]

I had the same problem as GT500 with my cq20v. Large bumps would kill the engine, turned out it was the elecy part of the ignition switch. If you wiggle the key in the ignition lock does it cut out?

Fuel pump will be a soft cut, i my car runs for 30secs or so with the fuel pump unplugged before it splutters and dies.

[S2central.net]

Yes - I have heard of this also... I know a couple of guys with S2's that have had this - seemingly its a common niggle on the Audi 80 and Coupes. Well remembered !


Paul