I have a 97 XK8, sometimes it will not start from very cold. (During summer months it starts every time). When it startsfrom cold it will do it after ther first or second turn over. If it takes more than 3-4 revs it will not start, but, if I clean the spark plugs of any gas it starts OK. I believe my cylinders are OK as I did a compression pressure test on every cyl and got between 155 and 165 PSI holding on every pot with the engine cold (about 45-50F outside airtemp). I have heard about the "wash by" with fuel cleaning the cylinder walls, but if I am holding pressure I must believe they are OK. Has any body come across a problem where the cold causes the injectors to stay open and flood the engine? Is this possible? Can low quality gas be a problem?
I am also concerned about a a very 'quiet knock' when the engine starts to rev from idle (with a warm engine). When its at idle, no noise and when its at speed 2000, 3000, 4000 RPM's no noise I have read that when the chain tensioners are failing a 'rattle' can be heard, in my case I don't hear a 'rattle'. I would like to check my tensioners (just in case), but have not done this before. Does anybody have any photos or information regarding checking the timing chain tensioners?

Thanks
Dave

 

The 'quiet knock' when the engine starts to rev from idle (with a warm engine) is most likely the Valve Timing Control (VTC) units engaging. They use engine oil pressure to engage internal dogs within the VTC units. This activates the VTC and advances the intake timing. At approx 1000 rpm, The ECU sends a signal to the solenoid which opens a slide valve thereby activating the units. You are probably hearing either the solenoids activating or the dog teeth engaging inside the VTC units. It can be a fairly loud click. I thought my VTC noise was Primary Chain knock until I replaced both Primary and Secondaries and still had the VTC noise.

Chain tensioners are diagnosed with a cold engine at startup and are a 'rattle'; not a knock. It is unlikely this is a tensioner issue.