Hi guys, this is an interesting one. I bought a 2001 A4 Quattro 2.8, 5-speed with 131k miles. I got it for a song because it has engine problems. I was able to start and drive the car on and off the trailer. It seemed to run ok I didn't rev it over 2000rpm or take it very fast. I was actually surprised how well it ran because the previous owner stated that it had no power. There was some minor top end noise but not too bad. The previous owner replaced the coil pack thinking that was the cause of the decreased power but that didn't fix it so he took it to a local indy European repair shop. The car was still parked at shop so I was able to talk to the mechanic and he said that the driver’s side had low compression and the passenger side was good. He thought the timing belt had slipped and caused the one side to bend valves. The good side was all about 140 psi and the bad side had 40 to 50 psi. So I ordered up a head gasket kit and full timing belt kit. This weekend I decided to take on the repair. I hooked it up to the Vag-Com and ran a scan. It came back with fuel injector open circuits on all cylinders and then miss-fires on 1,2,3. I think previous owner or the shop might have unplugged each injector looking for the problem. The miss-fires on the passenger side seemed a little strange to me as the problem is supposed to be on the driver side. Now is when it gets interesting. I pulled the driver’s side head and to my surprise the valves were good and I couldn't see any damage. Other than carbon build up everything looked as it should. It was very clear that the valves have not contacted the pistons. When I started tearing into the passenger side (which is supposed to be the good side) I noticed that the chain tensioner was different than the other side. Upon closer inspection I noticed that the tensioner was missing the nylon/plastic guide pad. The piston also appeared to be fully extended. I was able to fish most of the chunks of the pad out of the head. The variable timing is the part of the car that I have the least knowledge about but I am wondering if the mechanic remembered incorrectly and it was in fact the passenger side that had the low compression. Is it possible that the problem with the tensioner could have caused the low compression? I am kicking myself now for taking the mechanic's word and not checking the compression myself. When I pulled this head everything looked good as well. The valves all looked good as did the pistons. The top end noise must have been coming from the chain/tensioner. I have a "parts engine" so I have a spare tensioner that I can put in. I just don't want to go through all the work putting it back together if I have a problem somewhere else. Please see the pictures below and let me know what you think. I have also attached the vag-com scan log.

So here is my main question. Can a malfunctioning chain tensioner cause low compression?
Is there anything else that you can think of that I should look for while I’m in there?

 

You should be looking at bad head gasket, bent valves, or bad piston rings. Those are the culprits of low compression. The cam chain tensioner When really, really shot, can cause misfires due to timing being off from a slack chain, but yours both look taught. Also, a bad cam chain tensioner is usually noisy as hell first. I'd imagine your problem is a headgasket, especially since its misfiring.

 

Both gaskets were good with no signs of any blow by. I'll try to post pictures of them tomorrow.

 

What do you guys think? Should I clean up the heads, fix the chain tensioner and button it back up or could there be some other hidden problem? The pistons/cylinders looked good, valves looked good and the head gasket looked good. I'm still stumped by the low compression. The wear on the rings should be uniform on each side (at least in the ball park) so I don't see them as the problem. I also have a parts engine that I could pull the heads and swap them in. Or Plan B, I found an engine with 104k for $800 that I could put in there and call it good.

 

I called the mechanic that originally looked at the car and he thinks that he may have misspoke about which side the problem was on which is good since all evidence was pointing to the passenger side. He also felt that the chain tensioner could cause the issues that the car was having. I think I am going to send the heads to a machine shop and have them checked out and have the valves lapped.

 

I have the exact same dilemma - only I haven't pulled the heads yet! Your outcome may save me the expense, I have zero psi on cyls 4,5,6. Timing was off, I figure bent valves. No sound other than cam chain adjuster a little clunky. Adjusted timing, everything lines up, still no compression.

I'm about to pull the head. Did you end up resolving your issue?

 

Fellas,

ITS a NO Brainer...

a tensioner that melted away/ broke etc. disappeared to the audi Gods...

Clearly will cause your engine to be out of TIME. great you put a tensioner back in.. DID you time the cams to each other...?

I dont have the how to on that or i would offer it.

I DONT believe you HAVE TO remove the head to remove the CAMS together and insert the missing tensioner etc. ( TIME CAMS HERE)


HOPE THIS HELPS...
( this chuckle head ...me) did the same thing

ADVICE:

PANT OR SCRATCH MATCHING MARKS on the TIMING BELT/ pulleys

AND HERE IS THE SUPPORTING TRICK...

PANT OR SCRATCH MATCHING MARKS on the pulleys/ WING THING WASHERS on the CAM pulleys...

WHERE THERE IS A WILL THERE IS A WAY.

PS... make sure to mark your CRANK PULLEY to BELT also...

PS i use office white out and mark two teeth near each other on one portion of the belt pulley combination and two teeth on another section

making it clear in case one mark gets scrubbed.


ENOUGH SAID? best wishes in your PRJ.