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[Kevin Wood]

I know it's been touched on before, but I'm going to play devils advocate. This is mainly because of my ignorance, and lack of understanding, and is not intended to offend or make me appear ungrateful. That is certainly not the case. But I'm at work and the cars not, and I'm pondering .....

So, the source of the problem is believed to be a misfire, the cause of which I'm searching for. Atm all roads are pointing to electrical breakdown somewhere, and the understanding that the subsequent racket is brought about by the misfire. Is it possible that its the other way round? That the rattle is mechanical and causing the misfire? Whilst I appreciate codes aren't apparent in every situation, should they be showing in this one?

For example, we mentioned oil and lifters. Is it conceivable that if there was a problem with dry lifters that they could cause the noise, and any subsequent misfire?

With any luck I'll open the cable tray tomorrow and 'bingo'!! But if not, I'm just thinking of the next path to take. Just a thought, because really I don't know what I'm talking about   

I would try a compression test to rule out mechanical issues, personally.

We had an issue with TheBoy's car after LPG conversion that turned out to be a bad lifter or two. Similar scenario. Started it after unrelated work to hear a nasty tapping noise. Kept starting it and stopping it while checking things, not wanting to run it too long. Convinced it was misfiring some of the time and sometimes not.

These cars do tend to flood if you keep starting them from cold, due to the rich mixture when starting cold, and that might explain the misfire. Couple of wet plugs perhaps?

The main problem is that it's notoriously difficult to diagnose an engine noise even if you're standing over the engine, unless you've heard exactly the same fault before, and impossible to do remotely.

Worth a compression test and then take off the cam covers and check each lifter is solid with minimal clearance to the cam circle, and can't be compressed by pushing down on it?

[jonny2112]

Yep, fair point pal. I guess I was hoping for something a little more obvious, and without having to undo the binding or cabling, which will be never be the same again. I only had a quick look before heading to work, which is why I posted, for the further guidance. A stretched cable would be hard to find amongst all that though! Now the cover is off I'll have a closer inspection, and probably replace my original coil pack while I'm there.

[jonny2112]

Thanks Kevin. Compression test still outstanding. I take it that the engine must be complete to carry it out, minus the plugs of course?

[Kevin Wood]

Another thing to ponder.. If you've got a misfire and a knocking noise there are two possible scenarios, in my view:

1)  Misfire caused by ignition or (silent) mechanical failure. Bore gets wetted with unburnt fuel and piston slaps, giving a knocking sound.

2) Mechanical failure such as knackered valve, completely deflated lifter, etc causes the knocking noise and is serious enough to cause a misfire too.

In scenario 1, if you squirt a little oil down each bore, turn the engine over with the plugs out, then restart, it'll probably run without the noise for a few seconds. In scenario 2, no amount of oil will help.

[Kevin Wood]

Thanks Kevin. Compression test still outstanding. I take it that the engine must be complete to carry it out, minus the plugs of course?

Nope. Just disable the fuel system by removing the two purple relays to the rear of the engine bay fuse box. Can do it with the plenum and manifold off as you need the throttle open anyway. (check nothing is going to get drawn into the intakes, of course, and remove any bits of rag you might have placed there)

[jonny2112]

Thanks Kevin. Compression test still outstanding. I take it that the engine must be complete to carry it out, minus the plugs of course?

Nope. Just disable the fuel system by removing the two purple relays to the rear of the engine bay fuse box. Can do it with the plenum and manifold off as you need the throttle open anyway. (check nothing is going to get drawn into the intakes, of course, and remove any bits of rag you might have placed there)

Excellent, thank you. That saves building it back up again first, and the lack of access to nearside coil pack.
In relation to your previous post, are you talking about a drop of oil into the plug well? Sorry for being daft!

[Kevin Wood]

Thanks Kevin. Compression test still outstanding. I take it that the engine must be complete to carry it out, minus the plugs of course?

Nope. Just disable the fuel system by removing the two purple relays to the rear of the engine bay fuse box. Can do it with the plenum and manifold off as you need the throttle open anyway. (check nothing is going to get drawn into the intakes, of course, and remove any bits of rag you might have placed there)

Excellent, thank you. That saves building it back up again first, and the lack of access to nearside coil pack.
In relation to your previous post, are you talking about a drop of oil into the plug well? Sorry for being daft!

Yep. Well, a squirt from an oil can. Worth a try. Might give you some valuable information.

[jonny2112]

Cheers pal. Something else to try 

[omega3000]

Cheers pal. Something else to try 

Jonny i think you should change this post title to "Oh what have i not done"  Seriously hope you can find what is the problem . Fingers crossed 

[jonny2112]

Cheers pal. Something else to try 

Jonny i think you should change this post title to "Oh what have i not done"  Seriously hope you can find what is the problem . Fingers crossed 

 

[JamesV6CDX]

Jonny, there is an easy way to prove if there is a mechanical issue causing a misfire mate.

The only possible mechanical issue that could cause a misfire, would be if compression was lost somehow, EG damaged valve, camshaft, or similar.

Compresion test it!!

[Terbs]

Jonny....I have been following this thread with interest. Cannot offer advice as I am not a mechanic.
However, I, and I am sure, hundreds of other members are just waiting with baited breath and willing for the ....'Yes Yes Yes' post to say you have fixed it.
With all my heart mate..I hope you get sorted soon

Tony

[omega3000]

Jonny....I have been following this thread with interest. Cannot offer advice as I am not a mechanic.
However, I, and I am sure, hundreds of other members are just waiting with baited breath and willing for the ....'Yes Yes Yes' post to say you have fixed it.
With all my heart mate..I hope you get sorted soon

Tony

+1 , always checking in to see if he has found the problem 

[Andy H]

I know it's been touched on before, but I'm going to play devils advocate. This is mainly because of my ignorance, and lack of understanding, and is not intended to offend or make me appear ungrateful. That is certainly not the case. But I'm at work and the cars not, and I'm pondering .....

So, the source of the problem is believed to be a misfire, the cause of which I'm searching for. Atm all roads are pointing to electrical breakdown somewhere, and the understanding that the subsequent racket is brought about by the misfire. Is it possible that its the other way round? That the rattle is mechanical and causing the misfire? Whilst I appreciate codes aren't apparent in every situation, should they be showing in this one?

For example, we mentioned oil and lifters. Is it conceivable that if there was a problem with dry lifters that they could cause the noise, and any subsequent misfire?

With any luck I'll open the cable tray tomorrow and 'bingo'!! But if not, I'm just thinking of the next path to take. Just a thought, because really I don't know what I'm talking about   

I would try a compression test to rule out mechanical issues, personally.

We had an issue with TheBoy's car after LPG conversion that turned out to be a bad lifter or two. Similar scenario. Started it after unrelated work to hear a nasty tapping noise. Kept starting it and stopping it while checking things, not wanting to run it too long. Convinced it was misfiring some of the time and sometimes not.

These cars do tend to flood if you keep starting them from cold, due to the rich mixture when starting cold, and that might explain the misfire. Couple of wet plugs perhaps?

The main problem is that it's notoriously difficult to diagnose an engine noise even if you're standing over the engine, unless you've heard exactly the same fault before, and impossible to do remotely.

Worth a compression test and then take off the cam covers and check each lifter is solid with minimal clearance to the cam circle, and can't be compressed by pushing down on it?

I have lost track of whether this engine has had a proper run since the work was done or whether it has had repeated cold starts

[v6man54deg Geffd]

not read all the posts but I worked for the V6 plant for years working on warranty and durability issues - as you replaced the thermostat i would say the following ( FROM EXPERIENCE):

there is a gap on the rear timing cover adjacent to the thermostat housing - this gap is large enough for debris to enter - we used to get ty-wrap cut offs enter this gap drop into the cam belt which used to act as another tooth on the bottom pulley - this would knock the valve timing out by a couple of teeth and the engine would sound like a tractor / diesel engine!

all that was needed to repair it was to reset the valve timing by refitting the timing belt and if the engine was not run tooo much 99% of the time no damage was done and the engine was ok


so i would remove the timing cover and check the valve timing - often the bit of debris would jump out so it took us a while to find this problem but it is very common