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  #21  
Old 23rd October 2013, 11:44 AM
ulfilias ulfilias is offline
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Hi There,

The two side covers of the belt were one of the first things off. I popped the middle one. The belt doesn't look particularly loose or bad. All teeth seem to be there and perfect. Turning the belt on the starter and the wheels and marks look to be in the right place. I think you would notice one tooth out, let alone 3 or 4. I don't think that it is the belt. It was changed about 60K ago, which is by no means new, but it also isn't overly old either.

Lee
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  #22  
Old 23rd October 2013, 12:11 PM
richyb66 richyb66 is offline
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Whay about a problem with the hydraulic variator that controls the valve timing. If that was playing up would the cam timing be far enough out to cause misfires?

If the cars runs ok from cold maybe the oil pressure in the variator is bleeding off when the oild gets hot???
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  #23  
Old 23rd October 2013, 02:55 PM
ulfilias ulfilias is offline
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Hi There,

Alas the car isn't now starting at all....It turns over with the starter and tries, but then backfires and stops
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  #24  
Old 23rd October 2013, 03:21 PM
richyb66 richyb66 is offline
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This does seem to have the hallmarks of the valve timing being out. Can you turn the engine over by hand on the crank pulley and see if the holes in the cam pulleys line up? I can't remember if there's a TDC mark on the front cover anywhere (TDC for number 5 cylinder) which is where you lock the crank when you change the cambelt.

However if you can't the 4 holes (actually a hole and a slot on each cam pulley either side of the centre bolt) to line up horizontally like they do when you fit the cam locking bar, then something is definitely out with the valve timing.
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  #25  
Old 23rd October 2013, 07:26 PM
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Goran Goran is offline
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Just a random thought, is the bank thats misfiring the same bank on which you changed the cam variator a while back?
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  #26  
Old 24th October 2013, 11:56 AM
ulfilias ulfilias is offline
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Hi there,

The cam variator....As in the chain and lifter inside the engine. They were actually changed on both sides. Would seem strange that it has failed / chewed up the shoes in 50-80 thousand miles, possible. However the engine still ran when either of those had died pretty badly.

I spoke to a mechanic friend who said it is very rare for a toothed belt to slip and jump. They usually break before that happens

Lee
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  #27  
Old 24th October 2013, 01:32 PM
ainarssems ainarssems is offline
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The data points to valve timing being out. I helped to diagnose and changed cambelt and tensioner on on 32V S8 with same symptoms as yours. The belt had jumped about 1 or 2 teeth on one side and 3 or 4 on the other side, there was no damage to the belt and it was not loose. The problem was that belt tensioner was not changed at last belt change(15k ago) and damper was not not working properly allowing it to bounce kind of like when shock absorbers are gone on car suspension. Or like boot lid shocks when they have failed without resistance. Shock absorber had some resistance but not even throughout the travel and almost without resinatnce in the half of the range. This allowed tensioner to move under force of spring only.While the belt tension seemed OK when static I assume it was bouncing around when running making belt slack either one side or the other. Belt was also changed as precautionary measure just in case it had hidden damage from jumping over. After belt and tensioner change and alignment with proper tools it was running well again.

On 40V engines you have chain tensioners as well that could affect valve timing, I am not talking about the worn shoes but the hydraulic part of tensioner if one of them is not getting oil pressure or is stuck in one position it could also cause the issue.

Quote:
I think you would notice one tooth out, let alone 3 or 4
I think it would be hard to notice it just buy eye. My friend had timing out on 12V V6 which similar locking system with locking bar as 40V V8 and you could not tell it by just by looking at it, even putting ruler across camshaft pulleys it looked like it's fine and holes align up. Only by putting locking bar in place it was determined that timing was out.
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  #28  
Old 24th October 2013, 09:27 PM
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Goran Goran is offline
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I have the 40V cam sprocket locking tool, and the crank locking bolt, if you want to borrow them to check timing.
Only drawback is you would have to come over to pick them up.
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  #29  
Old 25th October 2013, 11:25 AM
ulfilias ulfilias is offline
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I'd taken the Throttle body off and cleaned it and stuff. I did a Throttle Body adaption and the car then started running again, albeit back at the Load Cross check / Multiple missfires / 1,4,2 missfires!

Pulling coil packs and sensors and bits and it appears that once it hits the missfires stage it shuts down bank one completely and it runs of the 4 cylinders of Bank 2 (5,6,7,8)

Disabling sensors on bank 2 (cam variator, cam sensor) i don't seem to be able to start the car at all....Was just wondering if by disabling bank 2 you could get bank 1 running and thus prove the timing between the two is out ???

Am tempted to fabricate a timing bar as I have access to factory equipment and they don't look comples (a bar with 4 folds and 4 holes in a line)
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  #30  
Old 25th October 2013, 12:37 PM
SilverS8 SilverS8 is offline
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Have you done a compression Test on the cyll's on Bank no 1 and 2?

If timing is off i would imagine that results would differ between the banks.

Jan
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