PEvans

There are several helpful threads on misfiring fault codes. I benefited from others' contributions to the knowledge base and wanted to add mine for future searchers.

This is a 2001 A6 with about 140,000 miles, and about 40,000 on the timing belt.

The car suddenly began running horribly and we had it towed in.

The fault codes were:

P1347 - Bank 2 camshaft position/crankshaft position sensor
P0304 - Cyl 4 misfiring
P0306 - Cyl 6 misfiring
P0305 - Cyl 5 misfiring

In this case the misfiring was only on one bank (Bank 2, or the left side). Rather than some of the other possible sources of misfiring raised in other threads (ignition control modules, camshaft position sensors, or worn camshaft lobes), it turned out to be a completely failed top pad on the Bank 2 timing chain tensioner. With the tensioner pad gone the timing is all off.

We replaced the entire timing chain tensioner assembly (which requires dismantling the whole front end of the car). The valves and cam lobes all looked ok. We decided not to open up the right side cam cover; we figured there was no way to tell visually if the tensioner pad was likely to fail, and did not want to spend the $ to replace the tensioner assembly "just in case." We did replace the timing belt since it was sitting right there.

PEvans

^^^ Sorry, 2.8L engine.

GTA_Driver

Thanks for sharing! When the misfire is confine to one bank, coupled with cam pos sensor errors, you could bet it's timing-related.

Thankfully you didn't bend any valves.