Hi,
I am having a bit of starting trouble with my C180. Basically everything was going fine then one day it was problematic starting when hot.

Generally it starts first time in the morning, and once its running it goes fine. If I stop the car and start it straight away it starts first time. If however I stop it, wait 5 mins or so and try to start it the car doesn’t start until the second time (sometimes third) I try to start it (with the automatic cranking time given when you turn the car).

This all started in hot weather, and did once refuse to start when the weather was really warm (well warm for the UK anyway).

I have checked for fault codes and there is none. I have replaced the crank position sensor without any change. I have checked the coolant temp sensor (using OBD) and this varies nicely as expected.

Suggestions I have had include a lazy fuel pump, blocked fuel filter, and a faulty Cam position sensor.

The fuel filter was replaced about a year ago so is not due replacement, but can obviously get blocked anytime. I am however tending away from a fuel pump or filter as I believe that with an engine that has just been switched off (5-30 mins ago) the pressure should still be relatively high, definitely higher than after the car has sat all night. Therefore if there was a fuel issue I believe the car would be more difficult to start first thing in the morning (unless it was too high a fuel pressure).

Too high a fuel pressure should not cause starting issues unless the engine is being flooded which im pretty sure it isn’t. The Long Term Fuel Trim was around -2%, so although running a bit rich I think there is not too much of a problem there.

Another, most probably unrelated issue is that the fuel system only goes into ‘Closed Loop – Fault’ and reports that it may be running on one lambda sensor. However the pre cat sensor is fluctuating nicely and the post cat sensor is around a constant 0.7V so both look ok.

Short of replacing all the fuel system I am starting to be at a loss what may be the problem here, and don’t particularly want to replace components on spec so any advice someone can give would be most welcome.

Thanks in advance,

A

 

having a similar problem on my c320 2001.
have checked relay, replaced crank sensor but am getting no demand for fuel at the pump.
I used a separate 12v supply to the fuel pump and it pumped fuel to the rail and engine started and idled but would not rev probably because there is no demand for fuel.
I am beginning to suspect the rear SAM may be the cause so am looking for more info.