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Hi,

Last year i had a coil failure and changed and replaced all 8 coils. At that time the failure mode was continiues misfire on one of the cylinders. Some weeks ago i started having trouble again. The engine clearly was running on less than 8 cylinders, but only for a period then it become fine again. This has continued over the last weeks with short intervals with misfire and then it runs ok. When the failure occur the car feel the same as last year, but the failure comes and goes which is different from last year. The Vagcom showes Random misfire and misfire on cyliner 2. Since it was an on/off failure i started changing the spark plugs since it was due anyway, but it did not make any differance. I am now pretty sure it is the coils (could be injector, but i do not know the nature of a injector failure..?) and i plan to purchase coil and replace the one sitting on cylinder 2. I might purchase 8 and change them all as have seen suggested in other topics, but since i changed all of them 1 year ago i have to think about it..

Last year when i purchased the coils which are in use now i did it on Ebay from and US supplier. I start to wonder if the coils i purchased was of bad quality. I see that VAG part number i 06B905115E and read that this was an upgraded version (E) compared to the ones provided with the car, maybe mine is an older vesion as there is no serial number on them it is hard to tell. Is the VAG coild with partnumber 06B905115E the most reliable coils out there or is there other replacement coild out there which are better and more reliable?

Please advice.

Fredrik

another thing to check would be the injector O-ring seals

I had an intermittent mis fire on one cylinder after romoving my rocker covers for powder coating, seems i upset an already brittle oring causing the seal to break. I replaced all 8 injector O-rings and the misfire cured.

you might be able to hear a slight air leak it if it is this.

Why not just move the coil pack to a different cylinder and see if the fault follows, if not then you can attack something else. Have you tried moving the wires attached to the coil at No8 to see if the misfire starts?

Could be cylinder head gasket failure.

/humour

chunky79 wrote:Why not just move the coil pack to a different cylinder and see if the fault follows, if not then you can attack something else. Have you tried moving the wires attached to the coil at No8 to see if the misfire starts?

Chuncky,
Thanks for you advice.

My plan is to do as you describe. I just wanted to check up if there are coils out there which are better suited for the RS6 than the OEM ones so i am prepared.

Fredrik

Shoppinit wrote:Could be cylinder head gasket failure.

/humour

Shoppinit,

Lets hope not! The head gasket was replaced August last year, hope it is not failed already.

I checked the cooling water reservoir, no reduction in the level and no smell of HC. There is not comming white smoke either..

Could be cheap Chinese copies on ebay. I personally would never buy important ignition / fuelling parts from unsure sources.

To rule out leaky injectors, you can look down the bores to see if wet. Check for black smoke on start-up, rich running on the trim. If you've got an air leak somewhere you'd expect lean trim.

Might be worth re-torquing the spark plugs, I've had misfires on other cars from spark plugs coming loose.

Also, like Chunky says, swap the coil packs, bank for bank. If you misfire is consistently reproducible you can buy one new coil pack and swap its position until the problem goes away.

Same applies to injectors. Swap bank to bank and see if the misfire moves. Obviously you'll need a Vagcom to see which cylinder it thinks it's coming from.

Shoppinit wrote:Could be cheap Chinese copies on ebay. I personally would never buy important ignition / fuelling parts from unsure sources.

To rule out leaky injectors, you can look down the bores to see if wet. Check for black smoke on start-up, rich running on the trim. If you've got an air leak somewhere you'd expect lean trim.

Might be worth re-torquing the spark plugs, I've had misfires on other cars from spark plugs coming loose.

Also, like Chunky says, swap the coil packs, bank for bank. If you misfire is consistently reproducible you can buy one new coil pack and swap its position until the problem goes away.

Same applies to injectors. Swap bank to bank and see if the misfire moves. Obviously you'll need a vagcom to see which cylinder it thinks it's coming from.

Shop,

Thanks for your input. Very much appricated.

Fredrik

Solved!!

Replaced coil on cylinder with intermitted misfire, problem solved. Since the so called original coils from Ebay seems to be everything else than original i changed all 8 of them.

Sounds like you got done with some cheapo copies. Glad it's resolved.