Hello and greetings from a newbie. I've read the posts on intermittent or sporatic starting or or dying from idle gradually getting worse.I replaced coil and checked that it does work. Looked at air mass meter and power stage (pulled elec. connections off then put 'em back on). Was making the usual start up sounds when it suddenly switched to an out of time start up sound. (like the cylinders not firing) Sure enough, compression is only about 50 to 75 lbs. in each cylinder. Pulled each spark plug and saw that they are sparking. Timing belt still on and the marks line up. Mechanic said bad block. I dont want to believe its dead and am going to at least pull head to look.

I increased the idle speed monthly (3 months) to keep it from stalling at idle. Car didn't run hot, has water and oil, and there is no water in oil. There is a crack in the exhaust manifold. I cleaned injectors in January and throttle body in september, replaced fuel trap screen last year.


my questions are these:

It is my understanding that compression is just a mechanical issue; however, I've seen so many references in this board to electrical device failure I wonder: if the timing belt is still on and the marks are located where they're supposed to, will the various electrical items like air mass sensor, radio suppressor, bad distributor etc cause the timing to screw up such that i would get lack of compression readings on all 4 cylinders?


I saw a maintenance FAQ on broken indexing pins in the camshaft and wondering if that would explain my problem?



1990 740 gle wagon, 200k

 

Electrical stuff won't have any effect on compression. But valve timing sure will. Remove the valve cover before the next compression test and make sure both valves on the #1cylinder are closed, and cam lobes up, when the TDC mark on the harmonic balancer is at 0. Test compression when engine is at operating temp, and throttle plate wide open. After each reading, squirt a couple of tablespoons of engine oil in through the spark plug holes and test again to see if reading goes up. If it does, then worn rings, bore etc. If it doesn't, then leaky valves or mis-timed a possibility .

 

The timing belt may be on but did you make sure it is turning?
Sometimes the belt will strip on the crank.Meaning the crank pulley will rip the teeth off the belt.

Are you sure you are getting fuel?

 

originally thought a fuel pump was to blame, but that wasn't the problem. Bought a timing belt, sure that would be to blame, but when we opened it and looked, i saw that the teeth were not stripped out (well, ok one tooth was missing) and the marks lined up. The car ran for three years without changing the timing belt.

any other ideas

thanks in advance for your help.

 

If you have spark and fuel it should run then.
Are you sure you have both at the same time.
Also make sure the injectors are pulsing.