audinutt

there is one other forum that has a LOT of d2ers...

I don't know if i can mention the name here.

q.u.a.t.t.r.o world

-richard

'01-S8

It seems that the cylinder misfires are random as well... different cylinders are misfiring when cleared and then re-started. Turn off vehicle and clear codes and start again and different cylinders misfiring......

audinutt

that is odd, so no correlation such a 1234 or 5678?
You did check your timing?
If you checked the timing I would get a compression tester (rent or purchase at local parts store) and test compression.


I am still wondering if your ecu isn't damaged somehow.

-Richard

silverd2

Agree with this...only so many things can cause random misfires and the ECU is one of em. Visually checking and cleaning the ECU is NOT testing it.
Valve timing is another cause...did anyone actually check the timing by the book, with proper tools: cranklock, cam gear lock? A belt being threaded correctly and tight does not indicate proper timing by itself.
Even though fuel pump and tank have been "disturbed", I would think that the fuel filter would have stopped any trash from making it to the injectors...mention this, because failed injectors throw the same misfire codes as a spark problems.

Again, by your own description, I'd start by looking to the ECU...IF you are certain valve timing is correct.

KEVOZS8

Yes that was it ! i didn't know they do not exist on the 40 Valves because my car is 1999 model 32 valves S8 .

'01-S8

Took whole front of car off and checked timing by the markings on the gears, pulleys positions as noted in the book... i dont believe he used the cranklock or camgear lock.

In voicing my problem to other VW/Audi gear heads someone mentioned that the rear timing CHAIN has a tensioner that could be out of adjustment or bad? I know the timing BELT is on the front obviously, but he said this motor has a timing CHAIN on the rear of the motor and a loose or fault tensioner/pulley could be to blame

Can anyone confirm this? Im going to do a bit of reasearch on that now and see what I can find. I also will be contacting Shokan to see what their cost of a replacement ECU is.

Thanks guys!

silverd2

Your motor has 2 internal timing chains, under the valve covers...the exhaust cams (driven by the timing belt) drive the intake cams via the chains. The heads are reversed from each other..the passenger's side (bank 1) has the chain and adjuster at the rear...the driver's side (bank 2) has the chain and adjuster at the front.

When the timing is set to TDC cylinder #5 (the ONLY way to check belt and chain timing) marks will line line up on cam chain gears, when correct (drawing below).

The tensioners are only in the 40V motors for variable valve timing function. Not likely to cause misfires unless one adjuster is badly broken...then only misfire codes on 1 bank...1,2,3,4 or 5,6,7,8.
When they go bad, you'll get a specific code. If a chain tensioner pad (nylon)is completely broken off (happened to me, no misfires), you'll hear a loud chain dragging sound under that valve cover while idling...AND likely get a timing code...example "intake cam over-retarded", etc..

If shopping for ECU's, I'd also look other places (no suggestion, off hand)...Shokan has the highest rip-off prices in the business for used parts...last resort only!!

PS: Audi S4 4.2's and later A8 (After '07?) FSi 4.2's have a large timing chain on the rear of the motor and NO timing belt...but not on your motor.

'01-S8

You think its possible that the chain is the noise im hearing and the motor just needs to be run for a bit to clear/clean it up???

It def sounds better/healthier than the first time it started... and i didnt think it sounded as bad the last (most recent) time I heard it run as the time before that.... at least i thought so ( could be me just being hopeful tho )

where can i find this nylon chain tensioner pad?? and if it IS broken where can i get a replacement?

silverd2

IF you have a missing pad, do NOT run the engine any more...not even at idle. Once the pad is off, the chain will eat into and destroy the tensioner in short order. I heard mine go on the way home one day and parked it until I repaired it. A new tensioner is a minimum of $550...best price.

Worst case: If you are missing a pad and the engine has gotten quieter, the chain has probably eaten so far into the tensioner piston that the tensioner is no longer salvageable.

Only 2 ways to know for sure...pull the valve covers or pull the oil pan to look for broken pieces of dark brown brittle nylon.

I bought my pads off ebay (Audi won't sell em...just entire tensioner)...all VW/Audi pads are the same for most years..designated #C062.

http://motors.shop.ebay.com/i.html?_...n+pads&_sacat=

NOT an easy job to replace and would NOT consider doing it without a Bentley step-by-step procedure. One bad move and you could destroy your head...HAS to be done correctly...every step.

Here: Passenger side (easiest, but NOT easy)

http://forums.quattroworld.com/a8/msgs/55496.phtml

'01-S8

But would this piece go from making no noise to being completely destroyed? The engine was not making any kind of noises previously....