Steven Smith
CCCUK Member
I am fairly sure the ECM in my 86 C4 has developed a fault and requires replacement unless anyone knows better?
Symptoms:
Engine will start from cold perfectly and run for around 30 seconds and then stall, when it cuts out all the fuel injectors can be heard to buzz randomly.
It won't then restart.
Diagnostic carried out:
I have spark and fuel pressure when cranking over to start but car won't start !
Fuel pressure is as per manual and doesn't drop when left, so injectors not leaking.
Resistance in all injector coils is around 17 Ohms cold and 16.5 hot.
When injectors are "buzzing" fuel pressure on the rail drops to zero so they are being activated.
Plugs are wet when it won't start.
With ignition on all injectors have 12v both sides of the coil.
The injectors are switched negative so the above is correct.
When the car cuts out the ECM is still randomly sending a negative to both banks of fuel injectors (batch fire system) even with the distributor wiring disconnected (ruling out the ignition control module).
The injectors carry on randomly activating until the plug on the ECM is disconnected and start again when reconnected.
The ECM is randomly sending the switched negative to activate the injectors when engine has cut out.
The distributor cap, rotor arm, coil, ignition control module and leads have all been replaced within the last 3 months (car still the same when refitted).
Any ideas apart from ECM ???
Symptoms:
Engine will start from cold perfectly and run for around 30 seconds and then stall, when it cuts out all the fuel injectors can be heard to buzz randomly.
It won't then restart.
Diagnostic carried out:
I have spark and fuel pressure when cranking over to start but car won't start !
Fuel pressure is as per manual and doesn't drop when left, so injectors not leaking.
Resistance in all injector coils is around 17 Ohms cold and 16.5 hot.
When injectors are "buzzing" fuel pressure on the rail drops to zero so they are being activated.
Plugs are wet when it won't start.
With ignition on all injectors have 12v both sides of the coil.
The injectors are switched negative so the above is correct.
When the car cuts out the ECM is still randomly sending a negative to both banks of fuel injectors (batch fire system) even with the distributor wiring disconnected (ruling out the ignition control module).
The injectors carry on randomly activating until the plug on the ECM is disconnected and start again when reconnected.
The ECM is randomly sending the switched negative to activate the injectors when engine has cut out.
The distributor cap, rotor arm, coil, ignition control module and leads have all been replaced within the last 3 months (car still the same when refitted).
Any ideas apart from ECM ???