QuestionAt wits end. Very intermittent fault ie sometimes impossible to drive, other times no fault. NB uses much fuel and seems "surgy". Fault when occurs is at 80 Kph or 105Kph ( approx 1800rpm )engine shuts down but will idle. push down on throttle you can drive through the fault but seems more to be two or three seconds it restarts itself without reengaging starter. Also can happen when trying to accelerate from rest but cutting out seems to be less time. This manifests itself at 1500 rpm its like hitting wall ie it cuts out, comes right, cuts out, comes right etc. Suspected throttle pot or similar to broken wire in loom.Removed cats, fitted dirty resistor,replaced plugs,replaced coolant sensor, tried another fuel pump fitted correct distributor rotor, checked compressions...don't suspect valve stick. Checked plug leads,base plate in distrib etc Uses lots of fuel. Trouble is when we hook up test gear eg scope etc , vehicle won't fault.One time we lost injector pulse entire left bank but inconclusive. Initial error codes AFM, ISC, TPS but all eliminated. Thinking of ECU ( possibly device accepting throttle signal ) .....Help please
AnswerOn a 3.9 with a 14CUX engine managment system and distributor, engine ECU failure is common and could produce these symptoms. Check the fuel pump, even though you have changed the pump. It could be a faulty pump or a blocked filter. But, losing pulse on only one bank does sound like an engine ECU as an ignition fault would cause complete failure.
The first thing I would change would be the ignition amplifier and the coil. Also put in a factory rotor arm as the aftermarkets are notoriously unreliable. Check the tune resistor, as well, which is down by the ECU because this drives the fuel injectors.
