Misfire

[Sideways_si]

Hi there just after bit of help if poss ph2 has developed misfire on Cylinder 6, changed 6 plugs and coils also injector in cylinder 6 but she's still not happy?
Any help appreciated

Regards Simon

 

[DaveL485]

Check the pins are sitting in the injector plug properly
Swap out leads, injector etc between cylinders to see if the fault follows a part
Compression test it

 

[Sideways_si]

Did compression all good, will run fine for about a minute then start misfiring?

 

[DaveL485]

If it's cylinder specific it has to be plug, coil, injector or something particular to that cylinder. As I said, swap stuff around and see if the fault follows.

I'm not sure if the vee is batch injection or sequential, on the 21 turbo for example it's batch so you can even swap the injector plugs around for fault finding.

 

[Sideways_si]

Looks like maybe internal fault with ECU,any recommendations for testing and repair would be much appreciated

 

[Kett]

SGM?

 

[ed_harland]

Looks like maybe internal fault with ECU,any recommendations for testing and repair would be much appreciated

Would seem an unlikely ECU fault more likely ECU plug connectors or the large multi connector in engine bay. If you haven't already test wiring continuity and resistance from ECU to injector.

 

[Sideways_si]

Checked wiring and plugs, have 3v coming down the earth trigger from computer with ignition on, and only 9v across injector when running?

 

[ed_harland]

Checked wiring and plugs, have 3v coming down the earth trigger from computer with ignition on, and only 9v across injector when running?

Are you getting the same readings on the other injectors ?

 

[Sideways_si]

Ya on all injectors mate

 

[DaveL485]

Injectors should have 12v ign live to one side from the injection locking relay, the other side is a switched earth to the ECU. The ign live turns on the injection relay which powers up the feed to the injectors, the ECU is only a switched earth - so the ECU itself does not contribute to the voltage supplied to the injectors; it only grounds the circuit to open the injector.

You should be able to manually feed 12v in to the positive side of the injection loom for testing purposes. Check the engine loom diagrams and you should be able to see what is what.

You can't test voltage across an injector when it's running, and the rapid opening and closing of the injector basically acts like a PWM signal and will only give a normal multimeter an "average" of the off/on time, they dont respond fast enough to changes. You need an oscilloscope or similar for that I think. You can only test for 12v coming in to one side of the injector when ign on, engine NOT running.

 

[ed_harland]

Injectors should have 12v ign live to one side from the injection locking relay, the other side is a switched earth to the ECU. The ign live turns on the injection relay which powers up the feed to the injectors, the ECU is only a switched earth - so the ECU itself does not contribute to the voltage supplied to the injectors; it only grounds the circuit to open the injector.

You should be able to manually feed 12v in to the positive side of the injection loom for testing purposes. Check the engine loom diagrams and you should be able to see what is what.

You can't test voltage across an injector when it's running, and the rapid opening and closing of the injector basically acts like a PWM signal and will only give a normal multimeter an "average" of the off/on time, they dont respond fast enough to changes. You need an oscilloscope or similar for that I think. You can only test for 12v coming in to one side of the injector when ign on, engine NOT running.

This was going to be my next comment ! Oscilloscope or some type of pulse frequency counter is the next step. I have no idea why you would have 3v on the earth from the ecu maybe the voltage dropped through the injector resistance. My thought was that if you were getting the same voltage readings at each injector even though it isn't the correct way to test that maybe if there were a fault, cylinder 6 would have a different reading.
It's important to check the end to end resistance of the wires between ecu and injectors as any increase or fluctuation (due to poor plug connectors or damaged cables which may only be evident when engine is running) will cause such problems. It may also be worth checking ALL the earths from the ecu.

 

[rustedandrotten]

Totally obvious but...have you checked the engine earth? Could be causing floating voltage?

 

[Noyzboy]

I read somwhere that there was a thing called a noid tester that could be used to check injectors. This is just hearsay cos it's way over my head