My 88 740GLE w/197k miles, seems to be running a tad hot. It never overheats but the temp guage is always a little past half when the car's at "normal operating temperature." The coolant has been flushed and thermostat replaced.
A while back, I failed smog due to high NOx numbers. The smog shop put on a new cat and retarded the timing to 11BTDC. The car barely passed smog. I did a compression test on the B230F and in 3 cylinders it read between 180-185 and the 4th read 190+. According to the Haynes manual it should have been between 130-160 PSI. Im unaware of any head work done to the engine so Im assuming there's carbon build up on top of the pistons.

I read the FAQ about carbon cleaning and was a little skeptical about doing the water and injector cleaner through the cruise control vacuum hose. Has anybody done this before? Im wary about hydrolocking the engine. And what about the possible rubber/o-ring degredation from the exposure to Sea Foam Green or GM Top Engine cleaner?

Thanx in advance,
Chris