E220 Intermitent starting problem

[jce220]

Hi folks,

I'm having a porblem with my '96 E220 and I really hope you can point me in the right direction to a cheap fix.

The car runs like new but over the last few weeks its started playing up. Sometimes it just refuses to start, then other times it starts instantly. The enigine turns over but won't fire, often if leave it a moment and try again it fires right up.

I have noticed that when turning on the ignition there is a humming noise then a plasticy sounding click coming from the throttle body area, I've just notived that if this doesn't happen the car wont start.

I really hope that makes sense, any suggestions would be great.

Many thanks.

John

 

[BlackC55]

124 or 210?

 

[jce220]

Sorry I'm totally new to Mercs and that meant nothing to me.

 

[BlackC55]

I am refering to the first 3 numbers of the chassis number.

 

[jce220]

Ahaa, thanks.

It's a 124

Does this make a difference?
Anyone had this problem?

 

[television]

The crankshaft position sensor is known to do this, very common fault

 

[jce220]

What is actually going on inside the throttle body when it hums for that few seconds followed by the little click after turning on the ignition?

Would a faulty CPS stop what ever this process is? I would have thought that if it was the CPS everything would hum and click as usual just fail to fire because of unsync'd timing?

I only question it as I would rather not spend £60 on a sensor if it's probably something else.

Your help is very much apprieciated.

JC

 

[Stevie A]

I'm wondering if the click is the fuel pump relay clicking on, and if it doesn't then the car doesn't start. Is this possible?

 

[Stevie A]

Actually could it not be as simple as a sticking part on the starter motor. I'd look into that, the fuel pump relay and what Malcolm mentioned.

 

[jce220]

The starter is fine, as I say it's turning the engine over normally but it's not firing.

The humming and click is certainly coming from inside the throttle body, I know when the car won't start as it doesn't humm or click, the engine still cranks normally just wont start.

Does anybody know if there is any kind of fuel cut built into the TB? maybe this is the click, I'm asuming that the humming may be the stepper motor.

 

[shirubaby]

my w124 hums and clicks. The hum is the fuel pump priming for start. The click I assumed was the fuel pump shutting off after prime (or turning on before prime...cant remember which).

There are other clicks as well - usually the duo valves but they are not connected to starting the car.

I wonder if it could be a faulty immobiliser? They tend to isolate the fuel pump when armed.