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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 1513
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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97 mercedes c280 won't start put in new crankshaft sensor

Customer Question

97 mercedes c280 won't start put in new crankshaft sensor plugs and wires still just turn over
Submitted: 9 months ago.
Category: Mercedes
Expert:  Juan Crespo replied 9 months ago.

Let us first try to find what is causing the engine not to start; is it lack of compression, spark, fuel pressure or injector pulse? Once we find which of those is missing, we can then focus on diagnosing the corresponding system and pinpointing the problem. Sounds good?

We should start by trying to start the engine with starting fluid; if it starts and runs momentarily, then we'll know compression and spark are good. If that's the case, then we'll need to test fuel pressure and injector pulse - we're looking for about 50 psi fuel pressure and a steady flash from a Noid light for injector pulse.

Please run those tests and get back to me with the results so we can continue.

Best Regards.

Customer: replied 9 months ago.
We have tried to start it with starting fluid still just turns over.we have spark on two cylinders only.the wires going to the solenoid all have voltage but it isnt giving any spark on the other 4 cylinders
Expert:  Juan Crespo replied 9 months ago.

What do you mean by "the wires going to the solenoid all have voltage"? what solenoid are you referring to? Any test equipment available such as HHT or capable scan tool, good voltmeter, scope?

Customer: replied 9 months ago.
Voltmeter.all the wires going to the coils have power
Expert:  Juan Crespo replied 9 months ago.

There are three coils; all get power through the Pink/Red wires, then each gets pulsed-grounded as needed by the ME-SFI control module to fire the corresponding plugs. The wires that the ME-SFI uses to ground the coils are: Black/Yellow for coil 1 (cyls 2 and 5); Black/White for coil 2 (cyls 3 and 4) and Black/Grey for coil 3 (cysl 1 and 6).

If all of the wires going to all of the coils had voltage, as you say they do, then none of the spark plugs would fire. As is, if it is true that there are two cylinders that have spark, and those cylinders happen to be the pair a given coil fires, then you either have a harness/wiring problem or a bad ME-SFI module.

Please let me know if you have any other questions or need any additional information on this issue.

Best Regards.