Misfire on Cylinder 3 - 2009 Aveo 1.2 - ECU Problem?

[Stokei_Nav]

Hello,

Me and my dad are trying to sort out an issue on my sisters 2009 Aveo 1.2L

The engine warning light came on and we scanned the OBD and it said that there was a cylinder 3 misfire.

We have worked through the usual things:

Replaced the Spark plugs
Replaced the Spark Plug leads
Replaced the Coil pack
Ran compression Test on all cylinders (and all are good)
Measured the resistance on all of the Injectors and they all show the same (12 ohms)

So all OK so far

We then measured the Voltage being supplied to the injectors and Cylinders 1,2&4 are getting in the region of 7V but Cylinder 3 is getting between 2&3 Volts

So my question is - is injector 3 faulty and the on Board ECU is just supplying less voltage as a result of it being faulty, or is it the ECU that is likely to be faulty.

We have re-seated all of the multi plugs on the engine (having sprayed with switch cleaner).

It would appear that Cylinder 3 is over fueling as the MPG has gone through the floor, the Spark Plug is wet when initially taken out (and quickly dries) showing that its petrol on the plug not oil.

On a couple of occasions when we were metering the Injectors we did get the error P0267 Cylinder 3 Injector Circuit Low.

Any help on this would be greatly appreciated

[Daox]

I would try swapping injector 3 with another injector. See if the code moves with it. If so, its the injector. If not, it is something else. ECUs fail sooooo rarely I never assume that is the problem.

[xintersecty]

An injector is a coil device. So it's basically a long wire. By measuring the resistance on the injector you can tell if it's in good shape. Measure the resistance on a known good cylinder and compare to the known bad one. If the resistance goes low it will drop the voltage V = IR

[Stokei_Nav]

The weird thing is that all of the injectors have the same resistance - when i measures the voltage the plug wasn't actually attached to the injector so t was purely the voltage that the ECU was sending out. We are swapping the injectors over tonight to see if the error moves to a different cylinder (and probably going to blow out the Injector 3 with an airline just in case there is anyy dirt trapped in there. thanks for your advice

[xintersecty]

Dang! I suspect you need to ohm out the wire. Since this is ground activate meaning that the ECU is turning a switch to ground it means you need to check from the fuse to the injector. the Pink wire.

[Stokei_Nav]

So - We swapped Injector 3&4 around and the misfire has now moved to cylinder 4 so it looks like a faulty injector....

[Daox]

Great to hear you found the issue. Injectors can be tricky. I've heard of more than one occasion where they work great until they get warmed up, and then they start having issues. Perhaps something is binding, or the coil is grounding out after thermal expansion. There are a few different things that could be happening.