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[05omegav6]

My 3.2 has been missfiring/generally running like poo ever since it destroyed a spark plug 40k ago .

Several Tech 2 sessions and replacement/swapping of various parts have all drawn blanks, with the live data showing nothing conclusive At best, the car won't idle smoothly, at worst it feels and sounds like the crank is making a bid for freedom. The problem is intermittent (aren't they always), but generally worse if left idling for a spell. Switching off and on again usually cures it for a bit.

Took it in for its Mechanical Inspection today ready for the plate renewal at the end of the month and was nearly blindsided The tester had left the car  running on the ramps while he jacked each end up to check the suspension etc and the 'engine' was missing and knocking like a bastid .

Two surprises:

1. The car has a slight misfire (ok that's not news).
2. The knocking death rattle that seemed to be the result of an issue causing 1. is in fact coming from the GEARBOX 

I've heard it for myself, so not a 'It needed a new engine, so we've done that for you and here's the bill' situation.

Diagnosis is that the LUK flywheel (70k old) is donald, which is upseting the timing and (you've guessed it) is in turn causing the misfire which the ECU is failing miserably to resolve. This may be a chicken and egg problem, in that the failure of the plug caused a severe vibration, which damaged the flywheel, but I wonder if perhaps we've all been looking at this from the wrong end both figuratively and literally

Any thoughts on this, or am I just chasing gremlins around the car

Incidentally, it only needs a track rod end
p.s. Apologies if in the wrong section, please move if felt appropriate

[JamesV6CDX]

I'm unsure how a dodgey flywheel can affect the valve timing? If the cambelt is all set up properly, I'd say that's not likely to be the problem? 

[Lazydocker]

I'm unsure how a dodgey flywheel can affect the valve timing? If the cambelt is all set up properly, I'd say that's not likely to be the problem? 

Where does the crank sensor take it's information from

Al, it's possible in theory. Perhaps a missing tooth or 2 from the flywheel but I would expect the issues to be there all the time

Only thing to do is pull the box and have a look at what's causing the rattle I think

[JamesV6CDX]

I'm unsure how a dodgey flywheel can affect the valve timing? If the cambelt is all set up properly, I'd say that's not likely to be the problem? 

Where does the crank sensor take it's information from

See your point, but If something had fallen to bits on the flywheel that badly to cause the crank sensor to play up and subsequently a misfire, I'd expect a fault code 

Also on V6, crank sensor is under the oil filter, so well forward of the flywheel?

[05omegav6]

I'm unsure how a dodgey flywheel can affect the valve timing? If the cambelt is all set up properly, I'd say that's not likely to be the problem? 

After a lot of indepth probing at the Lakes, the only thing found amiss was that the coil for pot six was showing 40kvolts rather than 60kvolts that the other 5 were producing. Tried 3 different coil packs with the same result.

Where does the crank sensor take it's information from

Al, it's possible in theory. Perhaps a missing tooth or 2 from the flywheel but I would expect the issues to be there all the time

Only thing to do is pull the box and have a look at what's causing the rattle I think

Missing teeth would as you say cause a permanent vibration which would vary with speed, in much the same way as an unbalanced wheel does.

But think to how a DMF works. As I understand it the two faces contain a number of weights, which float around the outer circumference (but within the flywheel), but can only move a limited distance, giving a damped inertia effect which gives the flywheel some added momentum and also reduces any crank/engine vibration. A bit like a spongy gyroscope.

Or a foam filled cake tin with several marbles evenly spaced around it. Spin this around its vertical axis, (like a fat flywheel), and the weight of the marbles will help keep it spinning smoothly even as the speed is increased/reduced. Remove the foam from between two neighbouring marbles, and spin it again, the result will be an un even/lumpy rotation.

If one of the damping springs is broken or one of the weights sticks at cerain temperatures/under certain centrifugal situations, then that could cause an untraceable intermittant problem. Wot like I've got

Several people all infinitely brighter than me have scratched and pondered and mused over this problem, but we've all been looking at the engine itself and the fuel/air control systems to try to get at the root of the misfire.

For reference the same esteemed peeps all played a part in the cambelt change, and I have no doubt in my mind whatsoever that the belt set up is spot on Did I mention that this is a frequently reoccuring INTERMITTENT problem which has manifested itself over the last 35k miles Belt was changed 41k ago

[05omegav6]

I'm unsure how a dodgey flywheel can affect the valve timing? If the cambelt is all set up properly, I'd say that's not likely to be the problem? 

Where does the crank sensor take it's information from

See your point, but If something had fallen to bits IN the flywheel that badly to cause the crank sensor to play up and subsequently a misfire, I'd expect a fault code 

Also on V6, crank sensor is under the oil filter, so well forward of the flywheel?

if you can draw any conclusions from 0300, 0306 and then if left for a period of time 0305 and 0304, then good luck

[JamesV6CDX]

  time for a new cambelt regardless then

[Kevin Wood]

Crank sensor on the V6 doesn't work off the flywheel, though. There a ring fitted to the crank internally. I'd be more inclined to think the rough running has knackered the DMF eventually, but not the other way around..

Might be wrong, though.

[05omegav6]

time for a new cambelt regardless then

Sad but true though not too high on the list of priorities if it doesn't run properly. 

Looking at about a grand of immediate expenditure on it if I keep it as a cab

VX Cambelt kit and water pump £140ish
VX HBV £25
VX Flywheel £180 (luk £400)
LUK clutch kit £230 (VX £650)
Bits and bobs £30
3 days off work £450 ish

Crank sensor on the V6 doesn't work off the flywheel, though. There a ring fitted to the crank internally. I'd be more inclined to think the rough running has knackered the DMF eventually, but not the other way around..

Might be wrong, though.

I'm in two minds Kevin, like I said it's a bit of a curveball because we've been working through the engine systems, but also a bit chicken and egg

[Lazydocker]

Crank sensor on the V6 doesn't work off the flywheel, though. There a ring fitted to the crank internally. I'd be more inclined to think the rough running has knackered the DMF eventually, but not the other way around..

Might be wrong, though.

Good point, although if it is a flywheel issue it could be having an effect

Like Kevin, I'm still unsure if it is a cause or effect though

[doz]

Just an idea. Do the v6's run knock senosrs? Is the gearbox/clutch issue causing them to "hear" something and fart about with the timing? I only mention it because with my Gsi Carlton you can tap the block near the sensor and make the the engine do all kind of strange things

[05omegav6]

I've been running it for the last fortnight or so with the 246 knock sensor unplugged, was better behaved at first but now playing up more often again. Though assuming that the dmf is breaking down, it will only get worse... The gear box is otherwise smooth and as quiet as you could expect a 200k omega 'box to be.

[05omegav6]

Quick update:

Both knock sensors disconnected, car still goes like it should, but spanner light is on . The engine idle speed is steady, but to look at it there is a definite vibration.
Gearbox knock starts up once the car has been left idling for 5-10 mins, but is intermittent, at the same time there is a slight shudder from the engine which make the EML flash briefly. The order of events is 'box knock starts, then the engine shudders, then the knock continues for a sec or two then stops.

Codes are 0330 Knock sensor 2   No surprise 
               0325 Knock sensor 1   No surprise 
               0300 Random misfire  If the flywheel isn't spinning smoothly, the the engine won't turn smoothly. Ergo Chicken and Egg problem/symptoms
               0306 Misfire pot 6 Really clutching at straws here. Could a 20kv voltage difference cause this

When the car was tested yesterday, it failed the emmissions test: CO and HC were almost at their minimum amounts, but the lamda was way out, 1.3 iirc

Retested today, (with new track rod end), and with the knock sensors unplugged, and the CO and HC were unchanged and the lamda was back to normal, 1.020

Now that the knocking noise is not being exacerbated/masked by the engine hunting as the ECU tries to keep everything in check does this shed any more light on the cause, or have I just added a ton of cement to the mud