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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53902
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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97 XJ6 Bad Missfire problem when warm.Put 6 Lucas Coils in

Customer Question

97 XJ6 Bad Missfire problem when warm.
Put 6 Lucas Coils in .
Idles perfect.
After 1700 RPM just cuts out.
No error codes.
Guessing crank or fly wheel sensor
Submitted: 2 years ago.
Category: Mercedes
Customer: replied 2 years ago.
1)Last winter installed after market coils when had a misfire.
2)Ran well.
3)This summer started crazy misfire with instrument lights off/on and engine cutout when driving.
4)Had to keep keep running to get home by keeping in low gear so engine would restart each time it cutout.
Work Done.
5) Next day it started OK, then acted up again when warm.
What I did;
1) Replaced electrolytic capacitors in computer.
2) Heated computer to 125F.
3) Start OK but missed at idle.
4) Installed new LUCAS coils.
5) Started and idled perfectly.
6) At about 1700 RPM it started to cutout.
Next Maybe:
Flywheel sensor DBC12508 and Crankshaft Sensor LHE1640AA from I have worked on many cars: 59 MGA Twincam, 84 Series 3, Mercedes Diesels. Have owned 50 cars.
Have found design error in MB OM603 engine. Thermostat on bottom on engine. Cold radiator keeps it closed.
Therefore be as thorough and specific as you can.
Expert:  Marty replied 2 years ago.
Hi Tom, sorry for the long wait. I can only offer you a guess based on past experience. I've seen the harmonic balancer come loose and cause too much air gap between the crank sensor and the toothed wheel on the pulley. I'd look closely at the front crank pulley and sensor alignment.
Let me know what you find.