Audi 80 Avant - Intermittant misfire ?

[kbowern]

I have an Audi 80 Avant with a ABK engine, which I call full fuel injection,
with an intermittant misfire.

Well it feels like a misfire. Very lumpy at low revs and lack of power,
but it still goes.

Over the course of time it's had a new coil,
distributor ( iffy hall effect sender ), new plugs, distributor cap, leads.

Problems goes away and comes back after various lengths of time.

I can find no pattern.

Just tried cleaning, Air Flow Meter sensor, not easy as it's in a plastic housing. Unsure if this has changed anything.

It passes it's emissions test at the MOT so don't think it's the Lamda sensor,
unless it's an intermittant fault on that.

Very tricky one.

[brd]

I have the same problem.... and was about to update my recent posts for when I asked for help... as I though it had gone, but unfortunately not.

I am checking another possibility at the moment which may be a cause. The vent on the petrol tank (which could be through the cap?) could be blocked... there was always a pssshhhttt when taking it off. I put the cap on after the last refill of the tank only half way (under the cover so shouldn't fall out - I hope! - but will get some cheap one that doesn't seal for the test)... and so far no problems with running. I need to drive more to see though as I thought I had it sorted before.
I do know that in changing the air filter, plugs, leads, dristributor cap (and soon the fuel filter) that it runs much better... but the stuttering was still there.... generally when hot and in traffic... but also on the motorway too.
I'ts been bugging me big time now for a while... so am trying my damnest to fix it as I use the car quite a bit. If you find something, do post, as I could realy do with ideas (if the fuel cap thing doesn't work)!

[kbowern]

That is another idea, something else to bear in mind.

At one point in time I did think that if I run the petrol tank low
I'd get the misfire problem. I was thinking I could be drawing muck
in from the bottom of the petrol tank. But it could be
a blocked breather pipe, as you say. I'll investigate.

[brd]

Damn... has happened again... the intermittant stuttering. Weather has warmed up a bit, and immediately its not running good again. I just got the fuel filter, so I'll check the flow rate from the tank aswell when changing it. I do go from full to empty to full all the time, so if there is rubbish in the tank, I may get close to it... but would expect the fuel filter to sort that out.

I'm going to check the water temperature sensor on the radiator aswell. I found a french manual that covers the ABK engine, so i have readings to check against now. Will keep you posted.

[adamss24]

Get a cheap OBD2 lead of ebay and an old type 2+2 adaptor for older audis and download the shareware version of vag-com on an old laptop and you should be able to see if there are any trouble codes in the memory !

[brd]

I like your thinking ... and have been considering that alright.... just not so sure which to get, nor where exactly it plugs in. You know?

At least maybe then I can test for errors when it's happening.... as its intermittant. I have already got two Audi garages to check it out, but they say nothing comes up on the diagnosis systems.

[adamss24]

The two conectors are inside the box on the driver side in the plenum/bulkhead and they are black(brown on some moddels !) and white in colour. Look for obd2 2+2 on ebay and you will see witch is it. They different in shape and wont go in the wrong plug. Check if there are 4 cables going to the conectors because if they only 3 the diagnostic wont work ! I had tried myself with great success on a l reg audi 80 2.0L petrol so i think yours will work just fine !

[kbowern]

since cleaning MAF ( air flow sensor ) car seems to be running OK, but
I haven't done a lot of miles recently so not really convinced

[brd]

I'll check that out... how did you clean it?
The car has been back in with Audi again... they still can't find anything wrong. Thankfully though I drove it to them with the problem actually happening and one of their guys took the car out and confirmed that there is a problem. Only, then he booked it in for the following week and it was running fine then... phew... ! Weather is colder now, and seems like prob happens less when colder.
Am running out of ideas now.... !

[kbowern]

I cleaned the air flow sensor with a solvent cleaner and a cotton wool bud.

If i did it again i would use "Ambersands" which is a de-greaser and just spray if on. I guess you need to be careful with what you use.

[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 :1zhelp: 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!