carterleeds

hi guys hows things...? i need help please

basically i changed all 8 coil packs about 4 months ago because the old ones missfired and came up on vcds, but now all 8 are missfiring again.

i had changed the MAF sensor because i was told sometimes this can cause problems but not come up on vcds, anyways the MAF is fine no problems registering with this, but just thought id mention it as this was changed same time as the coil packs.

any advise on what could be causing the coil packs to missfire...?

thanks in advance

MP4.2+6.0

If in U.S., there were service actions (a.k.a. "recalls") a few years back now that called back most Audis and VW's made in most of the preceding 10 years. My W12 got a new complete set of 12 coil packs as a result, even though I never had an issue. W12's are different than 4.2's here; they use the type used with VW VR6 motors. Not sure on the 4.2's. I did have issues on my 2000 4.2 A6 with two of them early on, but they conveniently only recalled back ten years to 2001 when Audi finally agreed to do it roughly in 2011 for the A6 group of 4.2's. Never an issue on the W12 with them (old or new), and no issue in years on the 2000 C5 4.2 though I did have to replace the 4.2 MAF along the way which I confirmed as partially fouled and that would throw sudden codes too.

If you are elsewhere, you would need to check on what if anything happened in your home country as far as recalls.

As far as your question, yes you should also question the MAF, and possibly either knock sensors or O2 sensors. But; you really need a good VAG COM or similar scan with the trouble codes before just throwing more parts at it, unless warrantied or in a recall action that is. Sounds like you have the tool, or access to it.

Also on MAF if you are suspicious, consider "instrumenting it" via data logging on VAG COM. Just log the engine RPM and MAF calculated flow basically. If you do data logging and have no co pilot, just go for a drive and start data logging hight before a few acceleration runs and click off afterward. The rule of thumb is you should see 80% of rated horsepower in grams per second. Thus on my old 4.2, I saw a peak of around 215 on what was then a 300HP motor, high up in first and second RPM wise; easier to see in second since acceleration is slower by then. The calculation says I should have seen 240+ g/s. Sure enough, post change I logged mid to high 250's. The power increase was also obvious and the oft recurring CEL went away--skipping over an unrelated tranny sensor wiring issue that overlapped it kicking into SAFE mode too.

ltooz_a6_a8_q7

Yes, mine were replaced in Nov 2010 - I don't know how long they would last -

carterleeds

thanks for all the info mp4 but i really dont have a clue how to preform those tests you just told me about. im a totall noob when it comes to vcds. i can do the bare minimum codeing and faults thats it

but however i have reset it and added some gas treatment cleaner from FORTE and it seemd to be fine no missfiring etc. so i dont have a clue whats going on. because it missfired for 3days and then when i was about to replace the ocil packs under warranty of course, the car was fine. so it may be the o2 sensor thats playing up and causing it to missfire. because i know the MAF and o2 sensor and coil packs are linked. however i dont know anything about knock sensors, whats there purpose? where are they? and how do i replace them if thats needed?

carterleeds

well seeing as i changed mine in august myself, i cant really go to audi because i would of just wasted money. i have a year warranty on these when thats up then ill probs check the recall you guys were talking about.

TSHong

Usually o2 sensors will not cause misfires. When they go bad, they will cause your car to run rich. The main thing is to figure out it's ignition or fuel related.

A knock sensor listens for spark knock or predetonation. If it senses spark knock, the ecu will retard the timing to eliminate the knock. This is to prevent engine damage.

subit0

How many miles on your spark plugs? Did you change them at the same time as the coil packs?

ltooz_a6_a8_q7

The VCDS can call out misfiring due to many things - it doesn't mean it's coil packs - I don't know why people or shops keep replacing them? My 3.0L cabriolet VCDS shows spark plugs misfiring every time I change or disconnect the battery. They run fine - I bought 3 spares and never used.

How do you know if the LOT of 8 coil packs are the bad ones? Put back the old coil packs. How do you know if your new coil packs are not the faulty ones that need to be recall? Now all 8 fail since you replaced them? Put back the old MAF.

To troubleshoot a problem - isolate and eliminate the problems one by one since you don't know how the system work - don't just go and shotgun everything down -

If VCDS says #3, move #3 to #6 to see if the coil pack #3 is the problem. MAF is the problem when my old 98 A8 die intermittently and then often.

Go back to where it was.

Cheers,

Louis

mishar

You didn't say how have you detected all eight of them misfiring. VCDS or something else?

From your other post it seems that your injectors are clogged so they are pouring instead of spraying fuel. That has same effect as lean mixture and can cause misfiring. Adding injector cleaner made it better. Just proceed with that treatment next tank and repeat it every third tank. Avoid low quality gas.

carterleeds

hi mishar. i think you have hit it on the head my little brother actually said it may be the injectors and that the fuel wasnt getting to where it should be going, because when i floored it, he mentioned that it may just be the fuel being blocked or clogged somewhere.

and i did notice by using crappy fuel it made the car worse. over here we have shell Vpower which is the best grade, well actually we only have 2 grades, normal and Vpower lol. but i did notice it made a difference with the misfiring. and im on my first bottle atm so will defo be carrying out what you suggested and fingers crossed.

may i ask, can the injectors be removed and cleaned or be replaced full stop? just a question not a task to be carried out.

and guys thanks for your input but with regards to

- subit0 spark were changed for service same time coil packs were changed.

- ltooz_a6_a8_q7 thanks but i did troubleshoot thats how i found the original coilpacks to be totally gone.

and sorry, yes vcds was used.