Won't fire.

[raving dave]

Hi there people.
Got a C220 elegance, 94 L reg, that will not start. Turn on ignition, fuel pump runs ok, all lights on dash, motor turns but will not fire. Had this problem a month or two back but it cured itself. Any ideas would be much appreciated.

 

[grober]

Test to see if you have a spark at the plugs. YOU MIGHT HAVE AN ALARM /IMOBILISER FAULT?

 

[mattkh]

Turn on ignition, fuel pump runs ok,

Hi
How are you checking this ?
Are you listening for it ?
Does the pump stop after a few seconds ?

 

[raving dave]

Thanks for replies. No spark at the plugs, but the alarm etc has been checked out ok.
Fuel pump runs for a few seconds to prime the system. You can hear this when you turn on the ignition.

 

[grober]

Try replacing the OVP relay---sounds as if your ECU is not triggering any sparks.

these engines have no distributer --just 2 coils each firing 2 plugs. The coils can go-the insulation on the wiring to the coils can breakdown due to engine heat. shorted coils/wiring can can blow the output of the engine ECU=EXPENSIVE! However it could just be the OVER VOLTAGE PROTECTION relay or even just its fuse which is mounted on to of it.

 

[kth286]

You should see if any fault codes have been set.

Where you located as someone can point you in the area of a specialist with a fault code reader for that generation of car ???

The crank position sensor is a critical one for starting, and a fault code would normally be set for that.

 

[grober]

It could be the CPS. They should measure a least 1Kohm across the connectors when OK ( according to television ). Normally they fault intermittently ----initially only when the engine is hot. They then work when the engine cools down only to fail again when the engine heats up. In the case of total failure like your situation there should be no continuity across the connectors at all. My money is still on the OVP relay tho.

 

[kth286]

The resistance of the crank angle sensor should be between 700 and 1400 ohms.

The insulation resistance should be greater than 20 kohms.

 

[raving dave]

Nice one Grober, vop was the problem. Removed it and gave it a tap, refitted it and engine started and ran sweet as a nut. Bought a new one, £66:39 incl vat, Merc dealers only.
Thanks also to everyone else who helped out.:bannana: