Audi 80 Avant - Intermittant misfire ?

[JohnnyBee]

Hi, chaps; I've just picked this one up from the list so I hope you don't mind a small suggestion; have either of you had the timing belt changed recently, or had cause to retime the front end?
I was foreman at Crypton Tuning in Brum for fourteen years, and you simply wouldn't believe the amount of customers we had in the place who had changed everything but the propshaft, yet missed the basic front-end setup.The dizzy is pegged (in theory!!) to remain in synch with the jackshaft, but if the jack isn't in synch with the crank/cam then the timing will be out.
Same goes for the cam; if that's half-a-tooth behind the crank then the bottom end pull goes right down the pan, along with the pickup.
It'd certainly be worth dragging the front covers off to have a look, and it may save you a lot more work in the future!
JB.

[kbowern]

Thanks for the thought : belt was change a long time ago, and timing was re-set after distributor change by an Audi mechanic with the computer box of tricks, although not at a Audi garage.

[VW Techniker]

Check ECT sensor - I've had lots of sporadic faults with these.
(This sensor influences fueling and ignition timing)

It's located in the coolant housing between No.3 & No.4 cylinders. If you connect a multi meter to the 'connected' plug from cold, you should see a steady decline in voltage, if it fluctuates or gives a constant reading, you should replace the sensor.

Good Luck

Rob

[brd]

I'd like to check that... but have a couple of questions. Could this give intermittant problems? It runs very sweet half the time.. and very lumpy the rest of the time... with no apparent pattern, other than it seems to mainly happen when warmer (i.e. not straight off from cold start). What you mean by 'connected' plug? I leave it connected and put the meter across the contacts somehow when the engine is cold? Would this show up on diagnostics? Cos each time when the Audi garage tries to find the problem, nothing comes up... but this can be due to the intermittant nature of the prob... ie fine when they check. Damn annoying. ... and thanks for the help.
Car is in with Audi

[VW Techniker]

I'd like to check that... but have a couple of questions. Could this give intermittant problems? It runs very sweet half the time.. and very lumpy the rest of the time... with no apparent pattern, other than it seems to mainly happen when warmer (i.e. not straight off from cold start). What you mean by 'connected' plug? I leave it connected and put the meter across the contacts somehow when the engine is cold? Would this show up on diagnostics? Cos each time when the Audi garage tries to find the problem, nothing comes up... but this can be due to the intermittant nature of the prob... ie fine when they check. Damn annoying. ... and thanks for the help.
Car is in with Audi

Hi,

Yes, this can certainly cause interm' faults and yes, leave the plug connected.

There are two different methods of "diagnostics"; Serial data ie through the OBD socket or intrusive, I prefer intrusive, its far more accurate. Personally I would use an ocilloscope on that sensor and record it over the warm up period; But multi meter should do just fine but keep you eye on the readings all the time, as you could miss any slight dropout.

Many garages say they have carried out "diagnostic tests" when infact they have only carried out a fault code interogation and 'if your lucky', may take a quick look at the live data, but because they dont know what to look for they tell you "Nothing showed up on diagnostics!".

Regards

Rob

[brd]

Thanks Rob,
Would this give any strange readings on the temp gauge if its measuring coolant temperature? I don't have any problems with the gauge, seems to be reading fine.
I got the car back again from Audi, still no solution. So now I think I have to start replacing some parts such as this ECT sensor, or the MAF, etc. As the MAF is a pricey option, the ECT could be a good start. I think they have been checking properly in the garage... it's on their time to get it fixed as I was given the car back saying it was fixed, and its their responsibility if not (other than parts) - useful french law I think. But I would have thought that the ECT would show up then on the diagnostics... although I know very little about the diagnostics side of things to be honest.
Thanks again for the help...

[joolz]

hi in a quest to sort out the random intermitancy of my a6 abk 2ltr engine i came across this thread having replaced the maf and still have the problem. apparently the supplys man in audi said he had only ever sold 3 units and would suspect something else, but because me and me mechanic mate had gone into the unit it would need replacing anyway. Having had many computer scans with audi vw and independants. i remember noticing temp guage wasnt working, it had just gone to poland and back with no probs so asumed previous owner had taken thermostat out to keep engine cool on long journey. So winters coming put thermostat in problem starts with vengance and since then replaced dizzy, rotar arm, ht leads maf, siliconed all electricals from damp all filters replaced new sparks, injector cleaner, will take themostat out tomorrow to see if eases the problem.

[joolz]

hi in a quest to sort out the random intermitancy of my a6 abk 2ltr engine i came across this thread having replaced the maf and still have the problem. apparently the supplys man in audi said he had only ever sold 3 units and would suspect something else, but because me and me mechanic mate had gone into the unit it would need replacing anyway. Having had many computer scans with audi vw and independants. i remember noticing temp guage wasnt working, it had just gone to poland and back with no probs so asumed previous owner had taken thermostat out to keep engine cool on long journey. So winters coming put thermostat in problem starts with vengance and since then replaced dizzy, rotar arm, ht leads maf, siliconed all electricals from damp all filters replaced new sparks, injector cleaner, will take themostat out tomorrow to see if eases the problem because the judder sometimes feels like its going to do damage to cam belt, engine mounts,exhaust system and my desire to drive the car.

[hunzan]

I have my Audi at the Mechanics at the moment still trying to find the cause was just wondering has anyone tried replacing the modulator in the distributor? and replacing the high voltage relay under the bonnet in the fuse box.

[brd]

Nope... haven't tried that... def be interested in results though!