Tekwon-V

vehicle: 1998 Audi A8 Quatrro 4.2L V8
mileage: 82k

ok guys, the car has been misfiring lately; displaying the check engine light. the 3rd cylinder seems to be the problem, after getting free scans at autozone. obviously it only happens after the car warms up. and sometimes the light goes away itself... and comes back. haha. it's magic!

i pulled all the plugs to inspect them. they are all fouled up. all greasy, wet and dirty on the thread as well as the tip. plugs were replaced at 68k with ngk platinum (4-tipped) ones at curry's auto (in chantilly) a while back. so, i decided to replace them with bosch platinum 4's. (50bucks!!! ahhh!)

while taking out all the coil packs, i noticed that ALL 8 of them had torn/ripped rubber boots..... not sure if it's significant enough for the rips/tears to cause the car to misfire... i am not sure.

i do not own a tq wrench yet (might get one for x-mas) so i did the standard "hand-tight until resistance, then 1/4 of a turn" with all 8 plugs, which turned out to be full 8 rotations. i put some anti-seize stuff on the thread too.

the car still misfires mainly on moderate to heavy throttle.... by juddering. i am going to look at the tq-spec on the plugs and see if an adjustment will help... but other than that.... i am not sure where to go from here. coilpacks are 80-100 each.... cant really try-it-then-return-it as they are special order items.

oh and what's the TQ-spec for tightening spark plugs?

thanx!

PaulW

There are tons of posts of us troubleshooting the problems:

1. Swap the black (or are they brown?) coil pack amplifiers (can't remember what they are called) under the cover just aft of the air filter.

They are both interchangable, they drive the 12 VDC to the coil packs.....if the cylinder that misfires swaps, then you know it's bad.

2. Swap coil pack three with another coil pack....if the cylinder misfire swaps, you know it's the coil pack....or the insulation or lack of insulation.

pw

A8CT

You're probably close the way you did it. You might just have one bad coil that's causing the problem. At least you know which cylinder to start with which give you a good headstart.

Bob

Tekwon-V

I do not have the service manual nor the vag-com

on the 1st thing you've recommended to do.... these "coilpack amplifiers" under the cover aft of the airbox... are they identical-looking pieces?

i will try both later tonite or tommorow. thanks guys.

Tekwon-V

thanks for your input. i will try it out.

Yanivic

Check if there is arcing. Start the car at night, pop the hood open and check if you see arcs flying around.. It must be the coil packs or plug wires...

Did you apply di-electric grease to all the connections?

escapA8

<ul><li><a href="http://www.audipages.com/Tech_Articles/enginemechanical/sparkplug.html">http://www.audipages.com/Tech_Articles/enginemechanical/sparkplug.html</a</li></ul>

PaulW

Yes, it's the two idential pieces under the cover, just swap them out....or try a coil pack first

PaulW

There are no plug wires on the A8, but could be the plug boot if ripped, don't know

backdoc

I had this problem this summer. It was the coil pack. If you know it is cylinder 3 that is misfiring, then switch cylinder 3 coil pack with cylider 4 coil pack and then take the car to autozone again. If the problem is at the #4 cylinder now, you know that it is the coil pack. Buy a new one, problem fixed.
DG
97 A8Q 112k