suming

I'm having trouble starting my E550

Took it to the mechanic and they checked sparks, crank position sensor and cam position sensor etc. Only had miss fire codes. Sometimes it starts up right away, sometimes it takes many times. Heard it almost crank over but didn't start. Once running it runs fine. Any ideas?

Thank you.
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CastorTroy

how old are the spark plugs? what cylinder(s) had a misfire? have the misfire codes come back? have you checked the fuel pressure after letting the car sit overnight?

when you say he checked the sparks, did he pull each one out and inspect it, check the gaps?

suming

Spark plugs are newish., the codes haven't come back. I haven't checked fuel pressure. The mechanic said he couldn't find Anythibg wrong. I'll check fuel pressure and clean Maf sensor. Could that help? Thanks bud

CastorTroy

well, when exactly is it not wanting to start? after it's been sitting for a day or two?

i'd start with attaching a fuel pressure gauge to the schrader valve after the car has sat overnight, check the fuel pressure, and then try to start it and see what the fuel pressure does.

suming

Usually first start of the day, it's not super cold here. Also after a few hours of not driving. Once it's been driven it usually starts up again quite quickly

CastorTroy

ok. that says to me a fuel pump issue. measure your fuel pressure after it's sat for a day and see what happens

eta: quick walkthrough https://www.mercedesmedic.com/fuel-s...hooting-guide/

suming

Cheers bud! Will do that. May mean I need a new fuel pump?