Firing on 4 cylinders!?!

[merlin's S4]

Driving home on friday night I completely lost ignition one of the cylinders. I recently changed the sparkplugs so my first port of call was to put the old one's back in. That made no difference! I'm suspecting a coilpack failure and I'm about to go and test them with an adjustable gap spark tester to see if this comes up with anything obvious! I'll keep you posted but in the meantime I would welcome your ideas and comments!

[Jas11n]

Driving home on friday night I completely lost ignition one of the cylinders. I recently changed the sparkplugs so my first port of call was to put the old one's back in. That made no difference! I'm suspecting a coilpack failure and I'm about to go and test them with an adjustable gap spark tester to see if this comes up with anything obvious! I'll keep you posted but in the meantime I would welcome your ideas and comments!

My bro went through something like this not so long ago. Here.

It reared it's ugly head again three weeks ago. We followed info from here and determined that it wasn't a coilpack failure, but rather a failure of one of the power output stages. You have a one time fix for this explained in that link as they have 6 channels and you can use one of the redundant ones. My bro opted for a secondhand POS from Sal though.

[merlin's S4]

Well the spark tester has showed up coil number 4. It was sparking intermitantly with a similar gap to the sparkplugs but when the gap was increased it wouldn't spark at all! All the other 4 coils showed a consistant spark! I swapped two of the coilpack boots just to check but there was no difference. Next is to find out whether it is indeed the coilpack or as you say (Jas) something to do with a POS.

May be ding that 1.8T conversion sooner than I thought!!

[AAH!]

When I had this problem I changed all my coilpacks and wiring amoungst other things none of which worked. Then as suggested by Doug_RS2 tried the unused channel in one of the power output stages (POS) by rewiring the connector and all has been fine ever since.

Trying this fix first is a much cheaper and easier option than replacing the coilpacks or the POS's.

as well as the SJM link above, see here:

http://www.s2forum.com/forum/showthread.php?t=11198

Angus

[mcandmar]

I second the pos units, just had the same problem on our S4, they caused intermitant rough running and occasionly went onto 4cyls at idle too.

[Corey]

ditto the POS, VAGCOM showed nothing.
On my happening it turned out to be a dodgy pin on the car side of the loom as it connected to the POS. Once it had been realigned car was fine.

Before spending anything check the POS and wiring

[merlin's S4]

I've got a spare set of POS units which I've tried this afternoon and this again made no difference. I've not looked at the wiring too closely as yet so I'll check that tomorrow. I'm still leaning towards the coilpack as I've had an intermittant missfire for ages. Mostly at high load situations but it has recently got worse and had started to do it more often at lower revs and throttle positions!

[Jas11n]

I've got a spare set of POS units which I've tried this afternoon and this again made no difference. I've not looked at the wiring too closely as yet so I'll check that tomorrow. I'm still leaning towards the coilpack as I've had an intermittant missfire for ages. Mostly at high load situations but it has recently got worse and had started to do it more often at lower revs and throttle positions!

What condidtion are the spark plug connecting tubes in? Just mention it as a guy on fans with a urS4 had exactly the same problem, missfire slighlty for a while at high revs/full load, then a total loss of that cylinder.

[merlin's S4]

I swapped the boots from another coil when doing the spark test so I don't think it's that! Is it unusual to have total failure of a coilpack then? With so many of you saying POS I'm unsure! Obviously I don't want to go spending money on things that won't fix the fault but the S4 is my daily driver and I'd like to get to the bottom of it ASAP. Is there a definitive way of diagnosing the coilpack??

[AAH!]

The coil pack wiring can get brittle from the heat and deteriorate, maybe this is what has happened. I don't know if there is a way of testing the coil packs via the connectors.