lI need some advice from more experienced MB owners. I have a 2000 S500 with 135K miles. Have had it for 3 years with minimal problems, but have a new issue I can't figure out. Car starts fine, but after short drive time (5 - 20 minutes) the engine quits. Usually at idle at stop sign or light. Engine cranks, but will not restart for a period of 10 minutes to 2 hours. I looked up this condition on the forum and 3 main causes seemed to be fuel pump, fuel filter/reglulator and Crank position sensor. I put a fuel pressure tester on it and it read 54 psi which is at the low end of the spec (54 - 63psi). So I first did a fuel filter/regulator replace. Did not fix, but when car ran, did get a steady 63 psi readout on tester. Next I replace the Crank Position Sensor. Drove is around the neighborhood for about 20 minutes and then brought back home and let it idle for about 30 minutes. Thought it was fixed, but went out the next day and it died after about 10 minutes. It did restart after about a 10 minute period. I am in Arizona where temps are running 100F to 106F this time of year. I have a hard time believing the fuel pump would be failing in such an intermittent fashion, but am open to any wisdom anyone could impart. Thanks guys.

 

Hi how long is it after it cuts out, before you can start it again ,and it runs. You could squirt some petrol in the intake after it stops ,then try to start it again if it starts its fuel related you will know then if it a fuel problem or not .Then look into fuel relay .

 

The time period varies. Sometimes only 5-10 minutes, but on two occasions it wouldn't start for nearly 2 hours. As the 2000 S500 is a direct injection, I can't really squirt any fuel into the intake. I will take a look at the fuel relay, but don't know how to really test it, but if it is not too expensive, I might just try replacing it.

 

Will your car have a throttle body on .I think you have a stepper motor in the throttle body .And not like the other models . The potentiometer is the part that goes bad. It might mean having ir re furbed.What you have is , as you put you foot on the gas the flap in the throttle wont move .So to check this out next time it stops remove the filter box ,ask someone to put their foot on the gas pedal ,do this right after it as stoped ,then look to see if the throttle plate is moving with the movement of the pedal.Fuel relay is expensive but you can get aftermarket one cheaper Before you do any of this i have told you about ,get a fuel pressure check first.Then see if you have spark at the plugs. Start with these 2 things first. A check for CPS is if it stops as you spin the engine over take a look at thee rev counter ,can you see it bouncing ,or trying to move .If so then you crank possition sensor is ok. Reading again your post i would get a relay as back up anyway.

 

Dfieldsh can you use YouTube videos .? Just put it in the search box in threre --- Mercedes S500 throttle body test . Just for an idea on the part and how the rebuild them .

 

I have been out of town and unable to do further investigation until yesterday. I did some driving and discovered that the engine shuts down just as it reaches normal operating temp. The ambient temp was around 110F and the temp guage reached approx 90C, which is normal much sooner and the engine shut down. Also, at ambient temp of less than 100F, it would start in 5-10 minutes while at an ambient over 105C, it would not restart for about 1 to 1 1/2 hours. I haven't tried the throttle body check yet, but do you think that the potentiometer would be so heat sensitive that it would work fine until outside air temps got over 100F and then fail only to start working again when the engine temp dropped? I guess it could be, but seems like a strange failure mode for a potentiometer.