2.4t cylinder one misfire mystery......

Evening all. Just bee lurking to try and find information but I thought I better post something instead.

I have a 2001 v79 2.4t (200) and it has a misfire. I know what your going to say but this happens only when it’s hot!!

Now the car has 175,000 and runs on lpg which is custom fitted before I bought guy it. Loads of history etc.

Anyways the car runs fine when cold but when it gets hot it misfired. I get a pending code and then a proper code which is a p0301 (cylinder one misfire detected). The car has almost new Volvo plugs which are gapped for lpg which is about 0.1mm less than normal. Pulled them out to inspect them all and cylinder one is blackened and wet from not firing. The rest are your normal colours. So I moved cylinder one and two around and started the car. It missed and before I did that I cleared any codes. Cylinder one misfire. Then I moved the coils. Same thing the fault didn’t move. I cleaned the earthing points on the head casting and cleaned the connectors and made no difference.

Fitted brand new coils and although the car starts a little better but still misses when hot. I then did a compression test on all cylinder with engine hot and I’m getting 200 psi across the cylinders. So as far as I’m aware the compression is good and yes all plugs were removed and throttle was wide on en. The car also misses in lpg as well as petrol so I have ruled out blocked filters or anything like that. Air filter is new also. Then disconnected the battery and shorted the power cables out and left it for half hour and then went under the bonnet and cleaned all earthing point I could find. I also gapped the plugs to 0.7mm to see if it would make a difference. Took the crank sensor off and cleaned that. That was very black and full of crud but yet didn’t make a difference after I put everything back together. Spark plug was tested against the head casting for sparking and I get small sparks when grounded to the head and they spark between the electrode and the tang and as you pull it further away the sparks are very bright and powerful so I think I have a good earth? Unplugged each coil when cold and the engine suffers and then regains strength. Done on all cylinders. When hot however I unplug number one and nothing happens but the rest react.

I’m running out of options here. I didn’t have a head gasket issue as that’s been recently done so no coolant in oil or the other way round. All filters and fluids have been replaced on including lpg.

What else can I do. I can’t think many more things that can cause a misfire. Is it worth putting a new crank sensor in. I have been told that everything is timed off of the number one cylinder.

Like I said it happens when engine is fully put temperature after about twenty mins of slow and fast idling and revving on both petrol and lpg.

Ryan

Tried another new set of plugs but made no difference. Then tried removing the thermostat to see if that would make a difference running it cold but again no different. Seriously need some hwlp

If the compression test was good, new plugs and coils, yet the misfire is still local to cylinder 1, then the only things left are the Valves (do any have a crack) or the Fuel injector itself.

It would be advantageous if you could inspect with a bore scope but TBH mate, I think you've exhausted everything and maybe you should get it into a garage.
If your good with spanners, then maybe you could replace the injector on No 1 but I fear your just throwing money at it, rather than actually diagnosing the problem.

It could also be a faulty plug, but my moneys on the fuel injector as you said it only does it when warmed up.

As its doing it in both petrol and lpg I personally wouldn't of thought it was an injector as they have seperate injectors for each fuel.
LPG is a dry fuel so makes it harder for the coil to produce the spark. You could try reducing the plug gap down from the gap recommend for petrol to see if that helps.
Does the misfire start only when the engine is under heavy load and on LPG? Just wondering if the engine management is detecting knock and shutting down that cylinder if indeed the Volvo management system does this in the same way SAAB does. Others may be able to advise on this. For the record I have had a couple of LPG motors.

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Originally Posted by Blackdog

As its doing it in both petrol and lpg I personally wouldn't of thought it was an injector as they have seperate injectors for each fuel.
LPG is a dry fuel so makes it harder for the coil to produce the spark. You could try reducing the plug gap down from the gap recommend for petrol to see if that helps.
Does the misfire start only when the engine is under heavy load and on LPG? Just wondering if the engine management is detecting knock and shutting down that cylinder if indeed the Volvo management system does this in the same way SAAB does. Others may be able to advise on this. For the record I have had a couple of LPG motors.

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Sorry but that sentence doesn't make any sense?

The coil producing a spark has bugger all to do with the fuel being injected, with ANY injector (LPG or Petrol).

AFAIK, if the engine management detects knock all it does is advance/retard the ignition, not shut down a whole cylinder by switching off the switching signal to the coil. You'll also need a multimeter or powerprobe with 12v digital read out to check wether you have

One thing is clear, the spark plug is fouling up black and is wet with fuel. So, clearly, that cylinder is not firing as per the fault code. So either it has a spark and fuel or it doesn't. Due to the fact this car has both LPG and Petrol and the misfire is present on both fuels, logic tells me it can't be the injector (as you said Blackdog). Therefore, it must be to do with the spark or lack of!

OP, you need to work backwards from the coil and confirm if your getting a switching signal from the ECU. You'll need a NOID light or an LED tester to check the switching signal to the coil and a voltmeter to check you've got 12v.
However, the first thing I'd do is remove the ECU and check that none of the pins are corroded on the ECU and that none of the tiny holes the pins plug into are corroded or have water ingress. If you don't have the tool to remove the ECU, then you'll need to go to a Volvo dealer/specialist.

The coil producing a spark has bugger all to do with the fuel being injected, with ANY injector (LPG or Petrol).

In short Lee in this instance you are wrong. But let's not take this off topic for the OP.

How so?

Put a 9v battery across your fingers and then your tongue... See which shocks you the dry fingers or the wet tongue.

Quote:

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Originally Posted by Blackdog

Put a 9v battery across your fingers and then your tongue... See which shocks you the dry fingers or the wet tongue.

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Oh, I see what your saying now. It was my interpretation of what you put that didn't make sense. So your saying that because LPG is a dry fuel, it's harder to burn because it doesn't conduct electricity aswell as Unleaded does? If that is true, it's still irrelevent in the OP's case as the symptoms of the misfire are present on both fuels once hot.

What I am saying is, The coil WILL produce a spark (if functioning normally) irrespective of ANY fuel (LPG or Unleaded) being injected into the cylinder. However, if that spark is weak then it may be getting blown out once the cylinder pressure builds up under boost/load and therefore causing a misfire or the same weak spark may be present due to incorrect/insufficient voltage to the coil in the first place!

Which is why it's important to check the correct voltage is present at the plug that connects the coil. If it is, then it kinda rules out low voltage and weak earth. Comparing the voltage whilst the engine is running is also important. So the OP will need to 'probe' the live wire to the coil with it connected and see if the voltage is good across all cylinders.

If none of this makes sense or what I've just said is not doable, then I'm afraid the only way forwards is to take the car to a garage for further diagnosis. If the garage is a good garage both mechanically and technically, then they'd have access to an Oscilloscope which will make diagnosing even easier.

I still think it's worth looking inside the cylinder with a bore scope too, just to make sure there are no cracks in the valves which will open up when hot! A cracked valve will cause a misfire and this in turn will cause the plug to soot up and remain wet.

Just to add as the plugs and ignition coils have been on and off many times the spring should protrude out the stem of each coil by 5mm.

If not so it can cause a misfire especially if the whole spring is not seated up right inside also?

Also did you fit the correct coils for your engine as there are some coils not suitable because of model?

I understand only one cylinder misfiring !