Intermittent start problem - Fuel pump/relay?

[89-300ce]

Sorry my search didn't work so I'll ask.

1989 300CE

I have now on two occasions had the car not start after it was hot and shut down. Continued cranking results in the occasional back-fire out the intake. After leaving the car alone for a while (15-20min.) it starts right up and runs fine. At his point I'm guessing fuel pump relay or fuel pump. Correct? Any way of testing these components? Thanks.

Jorg

[Ferdman]

Seems like it could be a vapor lock problem. Does your tailpipe emit a puff of black smoke when the engine is started cold? If so, the injectors may not hold pressure and allow fuel to leak into the cylinders. The reduced pressure in the fuel lines may permit the fuel to vaporize and cause a hard start/no start situation.

[janko]

pump or relay? the pump should be heard upon positioning the key in the on position. for a second or two. if pump is not momentarily energized, my bet is the relay.

[PHAEDRUS242]

Your symptoms sound like classical fuel pump relay stuff. The intake backfiring does seem a little strange, but that's probably the best place to start. We normally replace the overvoltage protection relay with twith the updated one when doing this repair. It's normally one or the other, and they seem to have similar lifespans from my experiences.

[89-300ce]

No, the car doesn't puff black on start-up. Never thought about vapour lock as its not that common a problem up here, though it certainly sounds about right.

I've never heard the fuel pump from inside the car when I turn the key. Do I stick my head under by the passenger rear wheel or could I hear it if I removed the rear passenger seat base (easy to do on a CE)?

[janko]

the pump/s are at right rear wheel. have a helper check for sound as you turn the key. again energized only for a second or so. and the relay i have in mind is naturally the fuel pump relay. just replaced one. around $110 from fastlane. so it ain't a pull and replace on a whim kind of thing. the new relay cured the intermittent starting problem my friend was experiencing. and she was very thankful.