Achtung Audi

I just got a '99 a6 with 2.8 and it is coming up with the check engine light and the codes say multiple misfire, and misfire in cylinders 4,5,6. I just had the timing belt changed due to unknown last time it was changed but made no difference. I did just find that my cruise control vacuum diaphram is tore open and needs replacing but I can't think of why that would cause it to misfire. Does any one have ideas on what could cause the low rpm misfire. This car runs nice and smooth at all speeds but when the rpms drop below the 1000 mark I can feel the engine start to vibrate.

Huskerbob

Post the codes please. Fix that cruise control leak and see what happens. Vacuum leaks and rough operation? Good place to start.

Achtung Audi

The codes are as follows:
p0300 Multi/Random cylinder misfire.
p0304 Misfire cylinder 4
p0305 Misfire cylinder 5
p0306 Misfire cylinder 6

I will fix the diaphragm as soon as my import parts store opens on monday.
I will pull the hose for now and close it off to check elsewhere for vac leaks.

Huskerbob

Read this. http://engine-codes.com/P0300.html This is a good site for codes in general.

Achtung Audi

I just ran a compression test and 1,2,3 cylinders are at about 130-135lbs
cylinders 4,5,6 are all at 165 lbs. Is that ok or is that whats causing this?

I could not find any vac leaks not sure how good my method was but no luck.

Airbag

wow . i wonder if you are off a tooth on that timing chain in the head ..

Achtung Audi

That was one of my concerns from the start. all 3 pistons on the one side are acting up the same. so i am thinking that would be a cam problem. what is the normal cylinder pressure supposed to be?

Airbag

well seeing your other side are all around 180, i would say 180 .. it varies a little bit by car obviously but should not vary within car by about 5% .

there are a lot of posts relating to be off by a tooth and some report comresion as low as 95, but the symptoms always apear the same as all 3 cylinders misfiring .. this would make sense as you are missing compresion.

Achtung Audi

I just find it odd that the side with better compression is the side misfiring. i am looking for some threads on cam chains off one link. please let me know of a good one if you have one.
i am also wondering if the cam tensioner not working right would cause this.

Huskerbob

On my rebuilt 2.8 I was pumping 200 lbs. on average. Not sure what normal is but I think having them all within 5 to 10 lbs. is the goal.

I think the one link off on timing is a good place to start too. Who did the timing belt work? Maybe they didn't count chain links correctly. It'll be easy to tell if you pull that valve cover. You can turn the engine over by hand, pull the plugs first, and see if your cam chain tensioner is moving up and down.