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Matt
Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 21094
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My Mercedes 230E (1996 model) would not start and I called

Resolved Question:

My Mercedes 230E (1996 model) would not start and I called out the AA, who said the problem was a faulty camshaft sensor located at the front of the engine. I ordered a brand new sensor, fitted it to the vehicle and the car started up fine. I dropped my Mrs in town and drove back home and parked up. She then phoned to say she needed to be picked up from town and when I went to start the car it does not start.

The engine turns over fine and there is plenty of life in the battery, but the car does not fire up. I re-called the AA (this is now aweek later as I've had to wait for the new part) and explained the situation. They say that they do not have the diagnostic equipment to locate the precise fault, and they add that it could now maybe be a faulty crankcase sensor.

Can anybody please help me diagnose this fault?
Submitted: 3 years ago.
Category: Mercedes
Expert:  Matt replied 3 years ago.
Hello

1st check for spark by removing one of the spark plugs and plug it back into its coil and rest it on the metal of the engine ( DO NOT hold it on place by hand) then have your assistant turn the engine over whilst you watch the plug. It should give a fat blue spark at regular intervals.

If not then check that there's power to the coil pack using a meter. If there’s 12V at the pack but no spark then check the ECU power supply (fuse and relay) and also the connections to the crankshaft speed sensor.


If there is a spark and its still not starting then its likely that the ECU isn't opening the fuel injectors, if the injectors are working you can hear them click - its difficult to hear them with background noise so use a long screwdriver like a stethoscope, placing the handle end in your ear and the metal tip against the body of the injector whilst your assistant turns the engine over.
If you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor and consider replacing this sensor if the wiring / connections look OK

If the car will start using a squirt of quick/ easi start into the intake then this confirms the problem is lack of fuel

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If you remove the filler cap to the fuel tank and listen inside while your assistant flicks the ignition you should hear it clearly
If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V.
You should be getting around 3 bar measured at the injector rail check to see if the plugs are getting wet indicating fuel is flowing – if not and the injectors are opening then there’s a problem with the pump or the filter or even the pressure regulator

Could also be incorrect fuelling due to a faulty water temp sensor. If this is the problem then the ECU will never add the 'cold start' extra fuel required if the car starts OK when warm then I 'd look into changing the sensor.
Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 21094
Experience: BEng hons Mech engineering, in auto industry 22 years
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