Starting major work on the red Jag - Checking Compression
Posted by Corey Thomas in Jaguar XJ6 compression on Monday, July 20, 2009
- Checking the compression on a 1987 Jaguar XJ6 Series III
The symptoms that I have on the car are that it hesitates under load and lopes on idle - sometime to the point of cutting off or almost cutting off. It also shows signs of running rich.
I started by checking the compression to see if there were any big things to note. I did the following steps:
- Stuck a screwdriver in the flap for the Air Flow Meter (AFM) to allow air in (to be compressed)
- Stuck another screwdriver in place to force the throttle to be open
- Disconnect the starter motor relay and added a lead to jump it directly to the battery - this is how I rotated the engine to measure compression without having to worry about fuel supply or the ignition system
I did both a wet and dry compression test. The dry was simply plugging the guage in a cylinder and cranking. To do the wet test, I added a teaspoon of motor oil in the cylinder and re-ran the compression test - a big difference here indicates wear around the piston rings.
Here are my results:
- Dry - 155 Wet - 170 (opened a beer and took a sip)
- Dry - 147 Wet - 160 (took another sip of beer)
- Dry - 95 Wet - 100 (finished the beer)
- Dry - 153 Wet - 160
- Dry - 158 Wet - 164
- Dry - 146 Wet - 154
- Re-test #3 - 95
Clearly I have head issues - most likely the head gasket.
Off with it's head...
More pictures here: Checking the compression
