Constant Misfire That Has Turned Into More..

[Josh]

Ok, here is my problem, I have an R34 GTT sedan with an R32 RB26 in it, controlled by a ViPec Plug and Play, has run fine like that for over twelve months, a while back I had an issue with the ECM staying constantly powered - draining my battery all the time, which turned out to be a failed Mosfet unit in the ECM itself, I solved that problem by putting a manual switch in the supply voltage line for the ECM power relay, as opposed to shelling out for a new ECM.

Now it has developed a misfire, It happens at all RPM/Load/Regardless of temp/Fuel level in tank. I changed plugs (Partly cos it was about time to anyway), all looked good when they came out. Unplugged coils until I isolated where the issue lay, No. 6 Cylinder, Swapped coils around to see if No.6 was faulty - Nope, coil ran fine on another cylinder and 6 still missed, checked actual spark to the cylinder - was exactly the same as all the others. Checked injectors, swapped No. 6 out - no difference, the injector from 6 ran fine in another cylinder and 6 still missed.

I unplugged the injectors one at a time to check the voltage across the plug while running (Not sure of actual spec, and I will add the car had no problems starting or running besides the miss at this point), all got, I think from memory, 0.3V, but No. 6 got nothing, So now I'm fairly convinced this miss is being caused by something further up the harness than the Injector. Checked from the ECM injector pins in the plug to ground, while running, all but number 6 got 0.6V, Number 6 got 12.5V...... Again I'm not sure what the spec is exactly, but the fact all got 0.6v and the only cylinder missing got 12.5v is a pretty clear indicator the problem is definitely Injector related.. but not necessarily with the injector.. Also I began to think of perhaps an open circuit in that injectors wiring or high resistance.

I also checked the ballast resistor and nearby wiring (due to the fact it runs through the LH wheel arch), No obvious breaks or abrasions to the wire, I checked the resistance through the common wire and each pin in the resistor and got ~6.7ohms for each of them (Which I read on another thread on here that is about normal for them). So I don't think the resistor is the issue.. The only thing I haven't been able to check is actual continuity from the resistor to the injector, and from the injector to the ECM due to shitty length of Multimeter cables and only having one set of hands hah.

So I find the resistor ok and go to start the car, no good, battery has gone flat.. This is where it gets even more Poo shaped... Hook the car up to jumper cables and charge for a bit, turn ignition on, fuel pump primes no worries, turn manual ECM switch on and the brown ECM relay does nothing but click about once a second.... I change out the relay, same problem.. I make sure the voltage is ok and see if engine will turn over - it does, and not sluggishly either - cranks like a pro...

And this is where I've got to now.. a bit stumped... Given the history I had with the failed Mosfet unit before and how the ECM is behaving now, I'm leaning towards saying IT is the cause of my miss, The different voltage to Injector 6 and now the failure to start/clicking relay problem is making me think its shagged.. The fact that everything else I've checked has turned out ok, which pretty much eliminates them as the cause.. Like I said before the only thing I haven't checked is continuity from resistor to injector and injector to ecm, which could show an open circuit, short, or high resistance at least..

Thoughts/Ideas anyone??

[GTSBoy]

Yup. Something bad in that ECU. The ECU triggers the injectors by switching on transistors to earth the injectors. Given it has a history of losing one mosfet already, you'd have to be suspicious of it doing it again. Can you borrow an RB26 ECU and try that. It may not run the engine, but you should be able to see if it triggers the injector. But before you do that, do check the wiring properly. If you need longer multimeter leads, just roll out some extra wire around the outside of the car to get the length you need.

[Josh]

Yeah that was my plan for it, longer leads with other wire. I have another ECM at home I will try and yeah it won't run, but should at least try to..

[kitto]

Sounds like the ECU has completely fried. Odd that you've had the power input transistor fail, then an injector transistor, and now the ECCS relay grounding transistor/control circuit start failing.

Yes power transistors that drive injectors do fail and have before on RB's. Not uncommon. Open up your ECU and have a look and see if there is burning on the ECU, possibly in more than one location.