Thread: V8 Misfire

Does anyone know how the coil packs work? Is it possible to have a fault with a coil pack where it doesn't fire just 1 cylinder or would all 4 cylinders fail?

Adam, when mine started to intermittently miss, I had the coil packs done as this was the cause.

Mine was only missing on one and sometimes two cylinders, so to answer your question, it doesn't have to miss on all four cylinders to be the coil pack.

I'd change them out when you can.

Yes, thanks, I thought that would be the case. I am pretty sure it is the coil pack that is faulty on mine. Looks like I will have to do the entire Cape York trip on 7 cylinders.
Is it possible to cause any damage to the motor running with a miss fire for an extended time?

I am in Cooktown tonight and there is no way I am going to get a new coil pack until I get back to Cairns in 3 weeks time.

Why couldn't it have failed a week ago!!

Adam.

It is insulation breakdown that is the death of plastic potted coils. If the misfire isn't yet 100% you may get some joy by reducing the plug gaps to LPG gaps, i.e. 0.6 - 0.7mm or 0.024" - 0.028". They run fine on dual fuels with these gaps.

A continuous electrical misfire will load your cayalytic converter full of unburnt fuel and it may get extremely hot and melt. Not really a good idea. I would check the condition of your spark plug and see if it is fuel wet or coolant wet. You could of course have a crook injector instead if your plug is clean and dry.

Thanks. The Disco had sequential injection LPG although I am only running it on petrol for this trip. However I did try running on LPG and it still miss fired which ruled out a faulty injector.

I will try decreasing the gap although I don't have any gauges with me so it might be hard to work out the correct gap.

Luckily I don't have any CAT's anymore so that won't be a problem.

The problem is worst when the motor is under load, so again I think this indicates a coil problem as well.

I do have a nanocom evo and I can monitor misfire with it. However I have no idea what the numbers mean on the misfire page. Is it the number of misfires per minute or something like that? Can anyone enlighten me.


Adam

Originally Posted by walker

Thanks. 1. The Disco had sequential injection LPG although I am only running it on petrol for this trip. However I did try running on LPG and it still miss fired which ruled out a faulty injector.

2. I will try decreasing the gap although I don't have any gauges with me so it might be hard to work out the correct gap.

1. The petrol injector is wired via the gas ECU, so there could be a wiring fault that affects both injectors, like the injector plug is loose on the relevant gas harness plug (assuming the gas fitter used a male/female injector cut harness). If so your spark plug will be clean. Is the miss present at idle? Listen at the exhaust. You would have to lift the manifold top to check if this is the case.
2. The thickness of an ordinary hacksaw blade with the paint off is 0.6mm.

Thanks again, all extra info helps.

As I said, the nanocom detects misfire. There is misfire at idle but not as bad as under load. It is felt worst at heavy load such as going up a hill in higher gear. Once it kicks back a gear it is a bit better.
The misfire is also inconsistent. Sometimes it is worse than other times. Once today it went away altogether for a good 20minutes and I thought the problem had fixed itself. We then stopped for lunch and it was present again once I headed off after lunch.

I didn't realise the petrol injectors were wired through the gas ECU. There are 8 seperate gas injectors and I always thought they were totally seperate to the petrol injectors.

When I pulled out the spark plug it was white on one side and black on the other, not sure if that indicates anything.

Originally Posted by walker

1. I didn't realise the petrol injectors were wired through the gas ECU. There are 8 seperate gas injectors and I always thought they were totally seperate to the petrol injectors.

2. When I pulled out the spark plug it was white on one side and black on the other, not sure if that indicates anything.

1. How do you think the gas system shuts down the petrol injectors? Each individual petrol injector is cut off by the gas ECU, its input signal read and translated in real time to that cylinder's gas injector signal.

The injector cut harnesses some gas fitters like to use are as dodgy as, I refuse to use them. The adaptor plugs are not good quality. All my injector cut wiring is done with solder and heatshrink instead.

2. Grubby is normal (maybe overdue for a change) especially if pulled out after cold running, wet with petrol is the danger sign.