Coilpack Testing Procedure?

[andrewd]

Thought it was about time I made an effort trying to figure out the cause of my UrS4's on-boost misfire.

I dug out UrS4Boy's excellent post on AudiWorld on diagnosing missing & hesitation, and I've gone ahead and ordered one of these:



Just wanted to go through what I think would be the procedure for testing the coils ...

I'll start by pulling the fuel pump fuse so that the car won't start.

Then I'll unbolt each coil from the cover and push them back onto the plugs (so that they are still able to fire a spark).

The one at a time I'll pull a coil (and boot?) off the plug and run it on the tester which I've clamped onto a ground, and then get an assistant to turn the car over while I see how far the spark will jump.

I presume after I've tested all five, one will stand out as being able to jump a significantly smaller gap than all the others and thus be the candidate for replacement?

How does that sound?

[kwlw]

How does that sound?

It sounds ok, however, how do you image to make around 10 bar of pressure in that tiny transparent chamber . When I saw industrial spark plug testing unit, they did that with air compressor.

Sau

[andrewd]

It sounds ok, however, how do you image to make around 10 bar of pressure in that tiny transparent chamber . When I saw industrial spark plug testing unit, they did that with air compressor.

Sau

Hehe. That could be a bit tricky! I guess that simply being able to wind out the gap is enough to be able to load the coil? And in this case we're just trying to test the coil's ability to put out power as opposed to testing a plug in realistic conditions.

[Fat Audi 80]

Sounds perfectly reasonable to me. The more voltage the bigger the jump. You should be able to find a "weak" spark with a little trial and error.

[UrS4boy]

Thought it was about time I made an effort trying to figure out the cause of my UrS4's on-boost misfire.

I dug out UrS4Boy's excellent post on AudiWorld on diagnosing missing & hesitation, and I've gone ahead and ordered one of these:



Just wanted to go through what I think would be the procedure for testing the coils ...

I'll start by pulling the fuel pump fuse so that the car won't start.

Then I'll unbolt each coil from the cover and push them back onto the plugs (so that they are still able to fire a spark).

The one at a time I'll pull a coil (and boot?) off the plug and run it on the tester which I've clamped onto a ground, and then get an assistant to turn the car over while I see how far the spark will jump.

I presume after I've tested all five, one will stand out as being able to jump a significantly smaller gap than all the others and thus be the candidate for replacement?

How does that sound?

All good except you DO NOT have to do anything to the coils. Leave them attached to the coil pack cover. Just test them one at a time with your tester (should have been available at a local car parts store BTW) stuck in the coil to plug connector, like a plug.

And yes, you are looking for the weakest coil, not the absolute strength, i.e. no need to pressurize to 10 bar. The weakest coil will be your suspect.

This assumes that you have checked your POSs and found them fine. (POS failure results in missing at all speeds including idle, whereas coil failures initially show up at WOT (high boost)).

[andrewd]

All good except you DO NOT have to do anything to the coils. Leave them attached to the coil pack cover. Just test them one at a time with your tester (should have been available at a local car parts store BTW) stuck in the coil to plug connector, like a plug.

And yes, you are looking for the weakest coil, not the absolute strength, i.e. no need to pressurize to 10 bar. The weakest coil will be your suspect.

This assumes that you have checked your POSs and found them fine. (POS failure results in missing at all speeds including idle, whereas coil failures initially show up at WOT (high boost)).

Thanks for that. As the misfire happens consistently only when hitting peak boost I'm tending towards it being a coil / boot / plug issue as opposed to POS. The plugs (W5DP0R) are less than a year old, and the boots are in reasonable condition. All coil wiring *looks* okay too.

I seem to remember having read that the coils that aren't being tested need to be grounded in order to avoid damaging them - hence my query about unattaching them from the cover so that they can still be individually connected to the plugs. I guess this could be accomplished in other ways though?

Thanks again for your help on this Dave (and others) - the internet is a wonderful thing for the S-Car owner.