Flooded engines after a brief cold start, then being left for a period is a common problem on modern fuel injected engines as we know.I even had a customer who did just that then tried to blame me because I'd serviced it 2 weeks before!
The really puzzling bit is why little or no compression sometimes?
I first saw this in the late 90's (with the advent of unleaded petrol) with a call out to a non-starting, flooded, as above Rover 620.
After trying all the usual, a compression test showed no compression so it was towed back with a suspected broken cambelt.As I took it apart there was no broken or jumped belt, no bent or stuck valves and no hydraulic tappets to jack open/collapse.
After much head scratching I took off the head, and still nothing obvious.As I dismantled the head carefully i found that all of the valves/seats were coated in a gritty substance not unlike coarse grinding paste, which was preventing the valves from sealing against the seats.The valve face and seats were in good order otherwise and after a gentle clean and lap in (just as a matter of course) it was reassembled , started straight away and all the compressions then checked and found to be good.this car was not an oil burner.
My own theory is that something in the petrol softens any carbon in the combustion chamber when soaked for a period of time.This then breaks up and manifests itself as a gritty paste preventing the valves from sealing properly.
This non-starting low/no compression I also saw a year or two later with my wifes own Ford Puma and later again on a Jag XJ V8. On both cars a scewdriver down the plughole lightly run along the top of the pistons retrieved the same gritty carbon-like paste, confirming my suspicions.
As I believed I now knew the cause, both cars started with some oil down the plugholes.I rechecked compression on both after restarting and both had compression completely restored.
I now always tell my customers to run their (petrol)cars for at least 3-4 mins from cold before switching off.
There will probably be someone out there to blow my theory completely out of the water, but otherwise I hope this helps someone.
(my 2p worth!)
Colin
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