Volvo S80 (1998 - 2006) - 98 2.9 Compression Problems

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Fri 9 Oct 2009 01:55
98 2.9 Compression Problems - CherryHillPI
The mechanic rebuild the head on this motor 178K and the motor would not start. He killed the battery, recharged it and got running. But at different times the compression now fails sporadically on various cylinders. We took in because number "2 cylinder had no compression. It died on the way.

Mechanic pulled head, had it rebuild, motor would not start. Finally got it running fine and the compression losses started randomly in different cylinders. He used two separate equipment to confirm it. So after rebuilding top end, new fuel injectors, swapped cold packs, many confirmed tests, we have a mystery motor.

Any suggestions on tests he can run? Will a new computer module help fix the problem.

We are stumped and will have to sell the car for parts if we can get a solution.

Any help is greatly appreciated.
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Fri 9 Oct 2009 10:18
98 2.9 Compression Problems - DP
The only thing that I can see which would cause intermittent loss of compression is when a hydraulic tappet "jacks up" and reduces the valve clearances to nothing, then clears again. I saw this once on a Rover engine belonging to a friend. In this case, a flush of the lubrication circuit solved the problem. This was an engine which hadn't seen servicing in some time though.

I don't know much about the Volvo engine, or even if it has hydraulic tappets, but every other cause of compression loss I can think of would be permanent (i.e. it wouldnt correct itself).

If it is genuinely a compression loss issue, a new module won't fix the problem. It's a mechanical fault.

I wonder if something was reassembled incorrectly relating to the valvegear or tappets, if the engine didn't have this problem before.

Good luck
Cheers
DP
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Fri 9 Oct 2009 13:10
98 2.9 Compression Problems - Peter D
Remove the plugs and place the cylinder at TDC compression stroke and connect a compressed are line in the spark plug hole. Listen for air in the inlet or exhaust. I would also suspect blocked hydraulic tappets. If you leave the piston there for 10 mins does the compression return ? Regards Peter
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