So yesterday we re fitted a proven cylinder head to the 2-4-6 bank, and re built the engine back up.
Pleased to say that compression on this bank is now fully restored - the readings being in the region of 190psi per cylinder
So even if the original head didn't look too bad valve wise - it was causing the drop
On this basis - we kept the original loom on there, as it looked as if the likely cause was now fixed.
Not long at all after startup, it was clearly idling rough, at the normal idle speed. The light began flashing . This led me to believe that perhaps the loom was indeed faulty!
Read the codes, and I had to do a double take - misfire codes for all the cylinders on the
1-3-5 BANK!! 
What confused me even more, is that I looked at the live data, and saw that the main Lambda on bank 2 (the bank no longer reporting a misfire) was reading only between 20-50mv. As this bank was no longer misfiring, I expected this one to be cycling normally.
I looked at the lambda for bank 1, and despite this bank being the one complaining, it's lambda was, according to live data, cycling normally, between 30-700mv at operating temperature.
I couldn't see how this could really be possible, if the bank was misfiring that badly, and thought it should be the other way round. For this reason we suspected maybe the lambdas were wired the wrong way around.
In order to rule out any closed loop problems, I unplugged all the lambdas to force it into open loop to see if it would run normally on a default map. It didn't - the problem was exactly the same.
I have been reluctant to believe it's the loom, up until this point, but at this point I began thinking - maybe there is something going wrong in the loom - and decided to change the loom for Robsey's 40k one.
So, new loom in place. Ignition on, clear of the codes, and a hopeful turn of the key.
No change. Misfire 1-3-5 bank, all cylinders.
I tried running the engine without the 1-3-5 coil pack, and it actually doesn't run much differently at all. Slightly rougher, + a bit of a popping noise, but it's not much different without the coil pack plugged in. So at idle it's running pretty much solely on the 2-4-6 bank!
When fitting the new loom, I plugged the lambdas in one by one, and checked "software" to ensure I'd plugged the correct ones in. So lambdas in the right place.
It was at this point, I began thinking to myself that I need once more to be looking at real basics. As my mindset has worked all along - don't believe in co-incidences, the 2-4-6 problem has now been fixed, but can't help thinking that we have obviously introduced SOMETHING to cause the new 1-3-5 issue.
As a test, I ran the engine at 2,000 rpm, holding foot steady on the throttle. The engine EASILY ran on all six at this point, without question. Sounded absolutely lovely revving and wasn't a problem in any way. As I did this, Steve reset the codes, and waited for any to come back. Despite waiting some time, holding it at 2,000 rpm, no fault codes came, and it didn't misfire. As soon as it was returned to idle - rough idle and pesky misfire, again.
I stood in front of the engine listening for any clues at this point. There is absolutely no valve train / lifter noise. I can clearly hear the 2-4-6 fuel injectors ticking away sweetly. However when listening on the 1-3-5 bank I wasn't so sure. (the injectors hadn't been shut down by the ECU at this point)
Whilst stood in front of the engine, we noticed a lot of metallic small noises, that I don't remember hearing on any other V6, coming quite obviously from the electronic DBW throttle control unit. Took this off for a look, I was thinking - is there a really silly fault, for example, has the air flap come loose from the spindle!! So took it off to check. very gunged up at the rear of the throttle bodies, where the butterflies sit (Steve will confirm!) And at the close position, it seemed to stick closed on this gunge. We gave it a clean, within an inch of it's life, and it was then no longer sticking shut. Refitted it and hoped we'd get lucky - NAAAH! Same as before. Misfire 1-3-5.
I tried the engine without the MAF - no joy - same issue.
As a test, I unplugged the DBW unit and ran the engine, to see if it would put it on a default map etc and see what that would do.
At this point, it coughed for a second when started, and the best thing I can describe is the sound of when an LPG car, which isn't running well on gas, is switched onto petrol, and then runs well, it was as if the cylinders on 1-3-5 just suddenly all stepped back into life, and the engine was idling absolutely A1 - albeit very slightly higher idle.
I'm no longer really sure what to make of this. Sadly I didn't have my kit to test the spark on the 1-3-5 plugs, but this coil pack was fine before, what are the chances of it suddenly failing! I don't think that's happened.
- valve timing is fine. Steve checked it after I setup the belt etc.
I did question myself, as you do, and think did I put one of the 1-3-5 cams on the wrong keyway, but this can't be the case, as all the valves would open and close at the same time and I wouldn't get any compression, no?? Also I don't think it'd idle OK at 2,000 rpm if I'd done that. In fact I know I haven't done that. I just can't stop questioning myself!!
Any thoughts would be greatly appreciated. We've spent about 20 hours and travelled 400 miles for this engine now, so it deserves to be fixed!!!
I had to down tools (at midnight) as I was tired to the point of not thinking straight anymore. I'm having today off, and will have a look at the car perhaps tomorrow, or early next week, with a clear head, hopefully armed with a few OOF ideas!
For now? I'm not going anywhere near a car. I'm off to walk my dog to the pub for lunch. Washed down with about three pints of doombar.
Author
Topic: Engine Loom (Read 33283 times)