Engine won't turn over on 1st try

mercedes-benz
e-class

#1

When my car as been sitting for several hours or overnight, the engine won’t turn over the first time I try to start the car. It always starts on the second try.



I had the fuel filter replaced, but it didn’t help. The mechanic wasn’t sure what the problem could be.


#2

Please define “turn over”, and tell us the make/model/mileage.

Do you mean the starter won’t crank the engine, or do you mean that the engine is cranking, but failing to start?

Since you replaced the fuel filter, I am guessing that it is the latter. That implies that the fuel rail is draining back to the tank while the car is turned off. There should be a check valve somewhere, likely inside the fuel pump, that prevents this from happening. Also, this may mean that that there is a small leak somewhere that is letting air in to the fuel rail up at the engine - like a dirty fuel injector, though the air may be coming up through the return line from the gas tank. If you crank the engine for a long while on the first try, will it start?

You should hear the fuel pump spin up when you turn the key to the ‘on’ position. It turns off once the system is fully pressurized. Normally, it can push all the air out of the system pretty quickly. Try leaving the key in the ‘on’ position for a few seconds before advancing it to the ‘start’ position. If that makes the car start quickly on the first try, you know that the fuel is draining back to the tank. If so, and that is your only problem, it is probably not worth the trouble to replace the fuel pump to correct it. I would just live with it.


#3

Thanks for responding so quickly.

The engine is cranking, but failing to start. Also, I don’t know if this is relevant, but it seems to happen only when the engine is warm or in warm weather.

1990 Mercedes 300E 170,000 miles