Okay here's the rundown:
Daughter's '81 300D sometimes felt like it was misfiring on one cylinder. She was doing a good job watching oil, coolant and everything. You know part of her learning to maintain a car.
She called from town, twenty miles away, and it had overheated. She had shut it down on the spot, "good girl".
When I arrived with gallons of water and tool box in hand, I could find no leaks or anything. Refilled the radiator, left water with her and followed her home.
It would overheat on the twenty mile run thereafter, same fire drill, and I believe that it was at this time that the misfiring cylinder became permanent. I told her not to drive it while I was on vacation. At this point, I could not find oil in coolant, or coolant in oil.
After coming back from vacation, I loaded up water and ramps, and drove twenty miles to the car wash to wash engine compartment thoroughly before tearing everything apart. It ran cool with no problems, even with 100 degree outside and running a/c. both ways. It did still have the dead miss. Still no coolant in oil or vice versa.
At this point, I loosened each injection line, one at a time, while idling, the engine seemed to falter equally on every one.
Was 90% convinced that I would find a dead cylinder when doing compression test. Tested compression this morning to find four cylinders between 280 and 300 psi while number 3 was 340 psi.
Now I'm totally perplexed. If the overheating problem was not involved, I'd think that the thing to do would be to dive right into the injectors or injection pump. When I moved the car out of the shop this morning to sweep underneath before tearing it apart, it still had a dead miss when cold.
Should I warm the engine and retest compression, even though it has the dead miss even when cold.
Any thoughts or previous similar experiences will be appreciated.
Wish me luck,
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in