What can caused the engine to cut out and not start again

[itallion]

hi Please can you guys help me

we have a 1989 m3 and it has a cutting out problem and then wont start again ..

we have changed crankshaft pick up sensor, all the usual suspects
then it ran for a few weeks no problem and then all of a sudden it starts cutting out again loosing spark .. I've been told it could be the ecu relay but I'm not sure where it is on the m3 , I know where it is on a 325.

please can anyone help

many thanks

[harry_p]

there should be 3 relays hidden behind the plastic panel on the bulkhead behind the coolant expansion tank.

from memory, from left to right as you face the car they are for lambda sensor, main dme relay and fuel pump relay.

i have heard that the fuel pump relay is the usual suspect for cutting out / not restarting when hot, but the fact you're losing spark suggests something else, it could well be the dme relay.

does it cut out whilst moving at all? if so what does the rev counter do when it cuts out? if you're coasting along and the rev counter is still working it suggests either a fuel problem, or an ignition problem after the coil. if the rev counter drops to zero it suggests a failier in the ignition power supply. there are a few non start hreads running in tech help which might be of use.

[itallion]

Thanks Harry will give that dme relay a try tonight

its cuts out while moving and the rev gage goes down istantly