W221 S500 won't start - does turn over though. Help please?

[wywywywy]

Hi all,

Basically I have a pre-facelift 2007 W221 S500 (aka S550) 5.5L petrol, and recently it has developed a problem starting.

The engine does tick over, and the battery is ok because I've charged it overnight. The breakdown cover gent sprayed fuel into the intake and the car started again.

Since then it's had about 50% success rate of starting, but once it's started it runs fine.

I got it towed to a garage but they couldn't find anything because sod's law it started fine every time while it's there. Also the computer shows nothing, strangely.

So it sound like the intake and ignition are fine, and the problem is in supplying fuel. But because it runs fine after starting, I *guess* it's not the fuel pump? But what else could it be?

Has anyone got any idea please?

Thanks.

 

[Gbrowncls55]

Crankshaft positioning sensor is worth a check for fault codes.

 

[zipdip]

Well it sounds fuel related ,have you tried getting somebody to turn the key to the second position and listen for the fuel pump to run,you should be able to hear this if you take the fuel cap off ,or maybe there is a air leak on the injection system,the good news is you have no faults when checked,so it is going to be something simple,famous last words I suppose.

 

[wywywywy]

Thanks for the answers.

I forgot to mention that if I keep trying to start the car in quick succession, with foot on the accelerator slightly, it will usually start after a few tries. Does this change anything?

 

[zipdip]

Still think it is fuel,just see if that pump runs when the car key is at the second position it is supposed to run before you turn the key to the third starting position,if the pump is running at least it rules that out,what about the fuel filter is that clean,again a quick check of that might help to narrow it down.

 

[wywywywy]

It is keyless entry so there is no position 2 as far as I know!

 

[kianok]

It is keyless entry so there is no position 2 as far as I know!

Press the start button twice without your foot on the brake.

 

[wywywywy]

I replaced the relay and so far it SEEMS to be working ok!

Fingers crossed hope it stays this way!

 

[MikeInWimbledon]

Did anything happen before the problem started? Did you run low on fuel or fill with fuel from some obscure rural garage?

Has the car been exposed to crazy weather conditions (especially wet / cold)

 

[wywywywy]

Not that I can think of. But the weather has been cold and wet lately yea.

Why you asking?

 

[MancMike]

Is it more eager to start when stone cold as opposed to hot start?

Symptoms sound exactly like the crankshaft position sensor and/or coolant temperature sensor to me. I had exactly the same symptoms recently, replaced the coolant temperature sensor, and cleaned the dirty/oily connector to the CPS and it's perfect again.

The CPS will flag a CEL, but the CTS won't, it'll just give incorrect readings.