V6 Misfire Timing chain Issue..

[jockmonkey]

Hi

Got a misfire on all 6 cylinders.

Mate of mine has diagnosed it as timing chain related, as on the osciliscope, you can see it firing on 1 and 6 not on TDC signal.

So its related to the timing chain..

Its a 2001 Sharan 4motion v6, with 80K miles and no obvious timing rattle from the chain

Do these actually stretch or is it damaged broken tensioners and guides making the chain slack..

Any ideas anyone??

[v6mikey]

I have heard of timing chain issues with the V6 lump, but not the Sharan. More so on the later models.

Have you tried VCDS to read error codes.

I bet that you have some kind of duff sensor.

I have a V6 4mo with 80K on the clock so keep us informed an how you get on.

[jockmonkey]

Read all the codes when he looked at it. He is a professional VAG technician with all the gear..

Codes cylinder 1-6 misfire (so 6 errors) P00301-P00306
2 others..
P00300 (multiple cylinder misfire detected)
P01340 Camshaft/Cranshaft signals out of sequence


Hence we wanted to eliminate sensors first, and it isn't the camshaft sensor or crankshaft sensor. We hooked it up on the osciliscope to see the actual electrical traces, and the engine is firing the cylinders off tdc for each cylinder. Hence the timing is out.

Only cause can be the chain. Hence wanted to know if anyone had had similar problems.
From forum searching, it seems like is more common in Golfs, but much more frequent in 4motion variants..

Jamie

[the_old_diver]

We hooked it up on the osciliscope to see the actual electrical traces, and the engine is firing the cylinders off tdc for each cylinder. Hence the timing is out.



Hi Jamie,
I'll start by saying I know nothing about your particular engine model and I'm just an amateur more familiar with Doxfords.

Two questions come to mind, firstly what is the connection between the timing chain and the ignition system ? I thought the chain operated the valves, while the ignition timing was electronically controlled by the engine management system based on data received from the crankshaft position sensor, plus other sensors like throttle position, engine speed , temperature etc.

Secondly, where did you get your oscilloscope reference for top dead centre? The crankshaft position sensor? I'd suspect that item or its connections.

Cheers, OD

[Crasher]

That is one seriously big job but yes both the 12v and 24v VR6 engines can suffer timing chain stretch at high mileages, if they fail the cost of the job will double. You must be absolutely sure this is the reason for the misfire as if you have that job done and it does not cure it, you will be a little unhappy.

[the_old_diver]

We hooked it up on the osciliscope to see the actual electrical traces, and the engine is firing the cylinders off tdc for each cylinder. Hence the timing is out.


Another point, Jamie.

I think you will find that many petrol engines work best when the spark occurs about 12 degrees before top dead centre... not that you can adjust these things nowadays.