98 a6 2.8 qttr 30V with no compression after timing job in #6 cylinder.
So after much repalcement of parts : maf, plugs, wires, ignition coil and throttle body cleaning in search of a mis-fire after timing rebuild I have isolated the issue to extremely low compression in one cylinder. Checked the timing 3 times with the cam locking bar and it is right on. Car starts and runs but with a bad mis-fire both at idle and under load. I've read and read with conflicting info: some say the engine will not run with bent valves , but it does. I've taken the valve cover off and watched things move as I hand turn the engine and the valves open and close fine - it seems.
Some say engine will have a nearbye cylinder weak if it's a block or piston issue and it does not.
Still stumped in Denver. What to do next?
Thanks.....

 

If the valves in the questionable cylinder aren't closing/seating completely you'll not get compression..right? Try this generic test: If compression is low in one or more cylinders, you can isolate the problem to the valves or rings by squirting a little 30 weight motor oil into the cylinder through the spark plug hole and repeating the compression test. The oil temporarily seals the rings. If the readings are higher the second time around, it means the rings and/or cylinder is worn. No change in the compression readings tells you the cylinder has a bad valve. The eaiest way I've read is electronically analizing it which any high tech shop can do but I'd try Audi first mainly becuse they can chat and have a cup with the engine

 

It'd be nice to know what you've found out..it's why forums work.

 

could be a burnt valve. A leak down test will tell you if it is rings or valves.

Air hissing in the intake manifold is the intake valve

Air hissing in the exhaust is the exhaust valve.

Air in the crankcase (Listen through the pcv valve or dip stick) are the rings.

 

Hi, yea I had good intent to keep plugging along but life got in the way. i am going to pull it back in the garage and will post! I have driven it around and even on the highway with the same results. It has not left me stranded and starts right up but with the lack of power from only having 5 cylinders firing.........I'll do the leak down test but i really have a gut feeling that the exaust valves are bent/stuck in the #6 cylinder. what am I looking at for time and money (tools) to go to the next step?

 

Low compression in one cylinder can be a burnt exhaust valve, bent valves from a timing problem, broken or worn piston rings, a blown headgasket, or a burnt piston. Most shops would pull the head to decide which it is since to fix any of these things will require the head off.

 

I agree with everyone here, all are good ways to detect the problem. Considering the problem came after the timing rebuild, I'm inclined to think its something with the valves or the timing. Perhaps a valve just isn't closing all the way, a piece of carbon stuck in the seat or something.