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Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 20614
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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I have a 2002 S500. The car starts without a problem, but

Customer Question

I have a 2002 S500. The car starts without a problem, but after 15 - 20 minutes have passed and the engine is warm, the car shuts down and will not start again until the engine is cool. We had a spark plug looking sensor in the top back of the engine replace twice because that's what we were told it was, but keeps doing the same thing. We are at a loss, what causes this action and how do we fix it?
A. Weaver
Submitted: 1 month ago.
Category: Mercedes
Expert:  Matt replied 1 month ago.

Hello

If you can get the engine hot so its exhibiting the failure then 1st check for spark by removing one of the spark plugs and plug it back into its lead 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 (at the other end of the plug lead) 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

Expert:  Matt replied 1 month ago.

Hi

do you still need help?

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