W140S420

I have a 1998 S420 W140, when I start the car in the morning it starts fine, but after I drive for a while and stop the car (turn engine off), the next time I try to start it, you have to crank the key a long time and push the gas pedal to make the car start. I've replaced the spark plugs already and all the fuses are working fine.

Any idea what could be the problem?

Hope someone can shed some light.

Thank you!

HedonisticFrog

It's likely the crankshaft or camshaft position sensor. Are there any other symptoms besides that? Does the engine have to get warm before it will struggle to start again or can you start it multiple times in succession while it's cold?

W140S420

This was fixed already. Took it to the dealer and fuel pressure regulator was replaced.

Thanks

HedonisticFrog

Thanks for the update, I just realized that's likely the problem with my 96 S420 as well which was blowing clouds of white smoke on acceleration and also having trouble starting. The fuel pressure was high with and without vacuum.

fabbrisd1

If engine is Warm/Hot - and hard to restart - then "very-very" likely culprit is Crankshaft Position Sensor - CPS - replace ONLY with Genuine Bosch Sensor like $45 - on the install there is a little washer between the sensor and crankcase - you need to re-use that - as that washer does NOT come with the Bosch OE sensor. If your "smart" get that little washer from your MB Dealer Parts Dept BEFORE you go to replace that sensor. There is probably a YouTube out there on the job