jokre

Hi!

I've got a problem with a vibrating engine. It has been rough on all rpms for some months now (even when standing still). It is some kind of engine misfire.

I have done the following without curing the disease:
- Changed spark plugs (all six)
- Changed ignition wires (all six)
- Changed ignition coil pack (all three pairs)
- Changed fuel filter
- Changed POS (Power Output Stage)
- Checked all electrical connectors I can find on the engine and cleaned them (such as injectors, etc)
- Checked both of the pre-cat lambda probes with Vag-Com and also disconnected the signal wires for the lambda probes in order to bypass the probes and force the ECU to go into safe mode regarding lambda readings
- Changed air filter
- Changed toothed belt along w/ new water pump, etc

I have also pulled fault codes with Vag-Com but that gives me nothing at all.

The car works and responds OK/ fair but it vibrates and it's really annoying.

The car is an Audi A6 2.6 V6 (ABC engine) Quattro w/ automatic transmission, m/y 1996.

Thankful for any suggestions that makes the car vibration free again!
// Jonas

DaveInSaltLake

you should be able to isolate it by removing the spark plug boots one at at time until you find the one that doesn't make a difference in the way the engine runs at idle.

Also, look for arcing in a dark garage.

Did you do any repairs or make any adjustments just before the problem started?

jokre

Thanks for the reply!

Yes, as I remember it (though it may be something that I have constructed afterwards in my head) it all started after I made a compression test on all cylinders and changed the spark plugs. I'm not sure though, but that is the only thing that I can remember. Is it possible that the ECU freaked out during this test and set the ignition the wrong way. Is it possible to reset this with Vag-Com?

Squirt-Tortuga

The ECU's on these cars aren't that smart. Most likely a bad plug, wire, or poor plug gap.

DaveInSaltLake

Is it possible that 2 or more plug wires have been switched? i.e. on wrong cylinders?

jokre

No, I've taken those on and off so many times so I know they are correctly mounted. In the last months I have changed the spark plugs, changed back to the old spark plugs (to verify that there where no faults on the new ones), changed to new ones again, changed ignition cables and changed the ignition coil pack, so I have had my portion of training to mount the ignition cables the correct way ;-)

DaveInSaltLake

The 1/2-inch diameter rigid black plastic tube shown below circles at least 3 sides of the engine. I've found it to be a bit troublesome when it's moved or bumped.

There are numerous other possible sources of vacuum leaks.

<img src="http://i47.photobucket.com/albums/f174/DavesData2/vacuum2.jpg">

jokre

Wires are recently changed to new ones. Spark plugs are changed to new ones and the old ones (that I know has worked) was mounted back to verify that nothing was wrong with the new plugs. As far as I get it, nothing is wrong with either plugs or wires.

jokre

OK! Thanks! I will check into that as well.

VOoDOoGTX

I heardO2 sencors will help that out. My car is doing the same thing. gonna change the O2 sencors.