Today I spent the day at BIGTime's place trying to find out what's going on with this. We had a good laugh and an enjoyable day
To recap. This is a 75k 3.2 V6 Omega in good shape. I have come in with some fresh eyes to have a look at what's going on with it.
The facts as given to me, are
1) Steve purchased the car. He did around 500 miles in it, with no issue. Nice and quiet, no misfires, no trouble codes, EMLs or nasty noises.
2) After driving it for these 500 miles, he took it for a Cambelt kit change, new cam covers, thermostat, and new spark plugs x 6.
3) When this work was done, immediately upon starting it, Steve noticed a very loud metallic noise, and the car was running like a bag of spanners. Not a faint tap - the kind of squeaky bum noise that makes you run for the key to turn it off!
4) Due to this, the car was immediately stripped down so the work could all be double checked again. The Cambelt setup (valve timing) was found to be fine. The cam covers were also removed - especially the 2-4-6 one where the nasty noise seemed to originate from, with a view to making sure there were no foreign objects. None were found.
5) After this was checked, the car was re assembled, and still sounded very "tappy". As the cause could not be found, Steve drove the car away, and has covered 300 or 400 miles or so since then.
6) In that time, the nasty metallic noise has now disappeared. Steve was however, left with the problem he describes in this thread, which is a misfire on the 2-4-6 bank, with present misfire DTC's being stored in the Engine ECU for all of the cylinders on this bank.
7) Steve has changed the coil pack on this bank in the hope it would cure it, for a new coil pack. No change - problem still exactly the same. This has basically led on to this thread, where Steve is now suspecting, and has been testing, the engine loom, thinking there may be an electrical fault.
Today's findingsI have basically come in as a fresh pair of eyes, to look at the facts and try and diagnose the issue objectively, and as such have started with the real basics, based around "why is this bank misfiring".
The first test I conducted was a compression test.
Results are, approximately, as follows
1 - 195psi
3 - 200psi
5 - 200psi
2- 115 psi
4 - 110 psi
6 - 90psi
So - the 2-4-6 bank (the one logging the misfire codes) is seriously lacking compression - the worst cylinder being around half the compression compared with the good bank. The test was repeated again with exactly the same results.
I checked the valve timing at this point to ensure some freak event hadn't caused the belt to jump. The belt was fine, the marks on the pulleys were in keeping with the marks on the setting tool with the crank locked at TDC - so the belt setup was OK.
I then removed the inlet manifold and bridge and looked at the inlet valves with a torch. The top of rear inlet valve on the bank with no compression was very black and sooty. The others quite clean.
I then removed the camcovers to check for any potential foreign objects. Nothing of note found.
At this point, the only thing for it, at this stage, was to whip the 2-4-6 head off for further investigation, so this is what I've done.
Pictures are below, but as you can see there is damage to the cylinder head around the valve area on each three cylinders. There is also damage to each piston, although I think we'll get away with smoothing the crowns a little bit. It's almost as if they have all had some bits of spark plug flying around in the bores (I think AL had this problem once, and possibly someone else too) - but on all three cylinders - AND just after it had been apart?
I don't have the old plugs for inspection, but Steve has seen them and thinks they were ok.
The next step is going to be to fit a known good head (one I have personally ground the valves into) and see if this restores the compression, and the misfire codes, and then take things from there.
Who knows - there may indeed be a loom issue - but - I have to fix the basic and obvious faults first, so they are taken totally out of the equation, before anything else can be looked at. And I can't ignore a 100psi compression drop as part of the diagnostic process.
A few pictures below. Steve's camera was playing up so they are taken on my rather dated iPhone, not the best quality but will give a good indication of what's been seen.
We are planning to do the rebuild hopefully later this week.
Steve and I would appreciate members comments on the pictures, and the circumstances/details I've described above.
Looking at the bore walls, they seem to have got away with it, there is no scoring, just the normal looking hone marks. The crank also rotates freely and the pistons move up and down OK.
I can only imagine that whatever has got chewed up in here, has somehow gotten into the valves and affected their seating, which is what has caused the compression drop.
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Topic: Engine Loom (Read 32658 times)