What causes a mechanical misfire?

[chrishamer]

So this thread is just out of curiosity really, but an audi main dealer has my A4 - 1.8TFSI 170 2012 in for repairs as the engine was misfiring.

They initially diagnosed a cylinder two fuel injector problem, but have since tried "2-3 injectors" and can't seem to fix it.

Their next step is to strip the engine as the mechanic seems to think it's a 'mechanical misfire'.

I'm just wondering what this might be or what might have caused it? I have the audi extended warranty (thanking my lucky stars I didn't let that lapse) but trying to understand what the issue might be?

Also, is there anything I should be asking them to do maintenance wise which might have a lower cost because they are stripping the engine anyway?

Thanks,

Chris

[Crasher]

Loss of compression due to valve guide wear causing an exhaust valve to seat poorly or a cam chain issue caused by wear due to the stupid long life (a VAG group “in” joke) oil change intervals and the crap oil we are forced to use that has had all the effective wear additives removed due to environmental legislation.

[chrishamer]

Loss of compression due to valve guide wear causing an exhaust valve to seat poorly or a cam chain issue caused by wear due to the stupid long life (a VAG group “in” joke) oil change intervals and the crap oil we are forced to use that has had all the effective wear additives removed due to environmental legislation.

Thanks, Crasher, I sense some frustration there but appreciate the explanation a lot!

Interesting what you say regarding long life oil, I did make a point of switching the car back to standard intervals, and I'm glad I did, even if it didn't spare me of this issue.

I'll let everyone know what the issue is, once I know. But my Audi dealer has now said they won't start stripping down the car till Wednesday / Thursday so I guess I won't know for a while...

[Crasher]

Oh there is frustration alright. The people who make the rules dictated that the additives in oil could not damage the cat because they have imposed such stupidly low Co2 emissions that manufactures have made piston rings so thin engines burn oil so they have dictated that the engine can get ruined but the cat can't-bonkers...

[chrishamer]

Oh there is frustrating alright. The people who make the rules dictated that the additives in oil could not damage the cat because they have imposed such stupidly low Co2 emissions that manufactures have made piston rings so thin engines burn oil so they have dictated that the engine can get ruined but the cat can't-bonkers...

Yeah, that is bonkers.

I hope my engine isn't totally ruined. Thanking my lucky stars on keeping the extended warranty...

[chrishamer]

Finally got my car back after over 6 weeks at my local Audi dealership...

The engine has been rebuilt and other than the injector(s), I've also had the crankshaft replaced and various other parts.

Seems to be driving well again, still can't believe how long the process took, but thought it might be useful feedback for someone else at some point.

[Crasher]

Rebuilding an engine is a time consuming proceed as it is not possible to know exactly what parts are needed until you are rebuilding, you always miss things and then have to wait and of course you don't give the car straight back, you test it for a few days. We are just putting the final touches to a Corrado VR6 engine rebuild, getting the parts has been traumatic!

[chrishamer]

Rebuilding an engine is a time consuming proceed as it is not possible to know exactly what parts are needed until you are rebuilding, you always miss things and then have to wait and of course you don't give the car straight back, you test it for a few days. We are just putting the final touches to a Corrado VR6 engine rebuild, getting the parts has been traumatic!

Thanks Crasher, yes I realise that it's a long process, it was more frustration about the parts of the process that seemed to have to do with the back and forth between the warranty department and the service department...

However, all seems well now, which is good. Hopefully it lasts another 50k, at which point I'll probably have sold it anyway.

Interesting to hear you guys are rebuilding a Corrado VR6, absolutely adored those cars, and especially that engine. I dread to think what the final bill will be on that, as I doubt there's a warranty involved there...

[Crasher]

I dread to think what the final bill will be on that

£5500 ish. Just told a chap with a 2010 TTS that his crank has eaten the block and itself because a thrust washer costing £8.90 failed and took out the turbo and the rest of the engine, going to cost him circa £9K....