Recently had the timing belt changed (along with all the other items generally changed - tensiors, water pump, etc).

Noted recently that the engine was misfiring. Read the codes back - indicating misfire on 1 and 2. I also get a code for misfire on 3 some times. This happens only at idle. More mis-fires when the car is cold.

I took it back to the shop that did the timing belt. They checked the timing, ignition coils, injectors, spark plugs, MAF etc. The misfire did not follow any of the coils, injectors when these parts were swapped.

The mechanic at the shop came to the conclusion that it is likely the head gasket.

Has any one had similiar experience? Could the head gasket on a car like this go? It has never overheated or had any fluid leaks.

Any suggstions would be welcome. I dread spending $2K to 3K on the engine.

Thanks

 

Since you are pretty sure that 1&3 are the problem , look at the coil harness for them to be sure they are connected well and not damaged. I would try to go back and think what was done during the belt replacement to see what caused it. If the problem happened after the belt, it was the belt replacement process more than likely. This process includes removing the coil harness. To check the headgasket, do a compression test, never guess at this one.

 

Thank you for your response. The shop swapped the harness from one side to the other. The misfire stays on the cylinder 1, 2 and some times on 3. It definitely is only on one side.

A compression test was done. It was okay as well.

I have read in the forums that the ECU needs to be re-flashed some times. Is there any way of checking if it is an ECU related issue?

 

I would find it hard to beleive that even if it is a head gasket that it would be causing misfires on all three cylinders. Since the problem doesnt follow the common electrical items like the coils or harness I would be very suspicious of the timing. Did they do the cam tensioner seals or pull the cams for any reason as part of the work done? If it was me I would remove the valve covers and line up the timing mark on the harmonic balancer with the mark on the plastic cover and look at the timing marks for the cams and see that they are lining up properly. If they are off it can cause misfires.

Just a note that the timing marks on the cams on that bank can be tricky the intake cam has the timing mark punched on the peak of a tooth rather than a valley like all the rest of the cams so when counting the teeth to reinstall it can be installed to the right or left of that mark and still be considered correct but if installed to the right of the tooth if you were facing the engine from the front of the car it is not correct and will cause different issues. sometimes it causes a code to show up for improbable cam position are you seeing this?

Just some thoughts but I really would be suspect of a timing issue if this started after the timing belt replacement. And as Oldmots stated you should be able to check the headgasket with a compression check.

 

Thanks for your suggestions - really appreciate it.

When I took the car back to the shop, they did open up the valve covers, put the car in "service mode" (i.e. take the bumper off and pull the rad forward) and check the timing. Apparently the timing was dead on. I did see the car at the shop with all the valve covers off.

It is possible that they don't know about the subtleties of the timing mark. I am not getting any other codes except for the misfiring on 1 and 2 and sometimes on 3. The car also drives great - no misfiring at high rpm.

They also did both a compression test and a leak test. Both tests turned out to be fine. The compression was between 150 and 170 across the various cylinders.

I am going to spend a bit more time on it this weekend. I have VAG-COM software and cable.

Once again, thank you for taking the time to post your suggestions.

 

bumpp

 

If it came from the factory with two, it still needs two. and yes it did, so yes you do.Have the exh shop drill and tap the pipe, and install it, where the harness will still reach.

 

I am still having this problem and now the car has failed to pass Smog because the misfiring codes. Does any one have any ideas on what could be causing this mis-firing?

 

socalvag, I had a similar problem a few months back(06 A6/C6 4.2). I was mis-firing 1,3,7 and 8 Cylinder. The most comment problems come in the small things. Check all the vacuum lines for leaks and clean them(diagram sticker should be on the inside of hood). After a few year the lines get toasted, start leaking, and clogging the vacuum.
I also recommend to take that time to clean the throttle body, spark-plugs and injectors if you can. Remember that all this components work together(little dirt could do some damage). If you get the line OEM they'll run under $100 and if you buy OE line that could run you under $5.

 

After failing SMOG, I decided to take the car into the dealer. They called me back within an hour of rolling the car into the shop with the news that the timing was not set right after the timing belt was changed. So inspite of the best assurances from the guy who did the timing belt that the timing was "dead on", it appears that it was not. The dealer fixed the timing (cost me $1300). The car now runs like it was right off the assembly line. The whole episode was a bit of an eye opener. The person who did my Audi's timing belt had done the job on my 2000 VW Passat 2.7L engine - which is essentially the same motor as the Audi 3.0. There were no problems with the Passat. He also tells me that he has done many 3.0L with no problems. I am just glad the engine was not damaged.

Padog was right after all - he had advised that I should focus on the timing. Thank you all for your suggestions.