94 E500 (119.974 engine) ignition problem?
 

1994 E500
119.974 engine
78,000 miles
new engine wire harness

Symptoms:

Intermittent rough running and occasional no start. When no start condition present, engine cranks, fires, but will not continue to run. Ocassional backfire also occurs when no start condition present. When rough running condition present, it is most noticeable at idle—idle speed is however still correct at about 500RPM. Engine smoothes out at higher RPM. Rough running symptom only occurs after a 5-10 minute warm up period, No start condition only occurs on warm/hot restart attempt. Cold start and initial run are 100% normal.

Retrieved a code 18 from pin 17—crankshaft position sensor. Replaced sensor, no fix.

Recheck for codes, none present.

This seems ignition related, it’s almost as if one bank of cylinders is not firing. I posted this problem on the 500E board and a few knowledgeable members suggested that I might have a failed/failing EZL ($$$$$$$$$$$$$).

Any suggestions on how I might proceed? I am considering replacing coils, rotors, caps and wires to see if that fixes the problem. Normally I don’t like to diagnose via part replacement, but I think these are all original so it probably would not be a complete waste if it doesn’t fix the problem. Also, the knowledgeable folks on the E500E site recommend new coils when installing a new EZL, so, if I end up needing a new EZL this will already be done.

Because a new EZL is so expensive, I want to rule out any other possibilities, so, can anyone think of anything else I might try/consider?

Thanks,

J. M. van Swaay