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Author Topic: Misfire Diagnosis  (Read 3099 times)

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Alex W

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Re: Misfire Diagnosis
« Reply #15 on: 19 July 2011, 20:42:59 »
If I had the cash I'd just swap the lot out and be done with it, but times are hard and the credit card is already groaning under the weight of my debts.
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RobG

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Re: Misfire Diagnosis
« Reply #16 on: 19 July 2011, 20:43:23 »
You can try pulling one lead at a time and see whether there`s a change in engine idle. Crude way to test the dis is to unplug knock sensor and start the engine, because of the higher voltage then required to start the car it will have a very pronounced misfire, but if the dis is faulty this option could kill it totally
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Alex W

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Re: Misfire Diagnosis
« Reply #17 on: 19 July 2011, 20:48:14 »
Quote
You can try pulling one lead at a time and see whether there`s a change in engine idle. Crude way to test the dis is to unplug knock sensor and start the engine, because of the higher voltage then required to start the car it will have a very pronounced misfire, but if the dis is faulty this option could kill it totally
I had hoped that changing the spark plugs might give me a clue about where my misfire was and how many cylinders were affected but sadly I could see no real difference between them as I took them out.
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RobG

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Re: Misfire Diagnosis
« Reply #18 on: 19 July 2011, 20:49:52 »
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You can try pulling one lead at a time and see whether there`s a change in engine idle. Crude way to test the dis is to unplug knock sensor and start the engine, because of the higher voltage then required to start the car it will have a very pronounced misfire, but if the dis is faulty this option could kill it totally
I had hoped that changing the spark plugs might give me a clue about where my misfire was and how many cylinders were affected but sadly I could see no real difference between them as I took them out.
Won`t make one iota of difference if any of the leads are donald. As suggested, try pulling one lead at a time
« Last Edit: 19 July 2011, 20:50:31 by RobG »
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Alex W

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Re: Misfire Diagnosis
« Reply #19 on: 19 July 2011, 20:57:34 »
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You can try pulling one lead at a time and see whether there`s a change in engine idle. Crude way to test the dis is to unplug knock sensor and start the engine, because of the higher voltage then required to start the car it will have a very pronounced misfire, but if the dis is faulty this option could kill it totally
I had hoped that changing the spark plugs might give me a clue about where my misfire was and how many cylinders were affected but sadly I could see no real difference between them as I took them out.
Won`t make one iota of difference if any of the leads are donald. As suggested, try pulling one lead at a time
I had hoped that the spark plug/s from the non-firing cyclinder/s might reveal the culprit/s.
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RobG

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Re: Misfire Diagnosis
« Reply #20 on: 19 July 2011, 20:59:26 »
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You can try pulling one lead at a time and see whether there`s a change in engine idle. Crude way to test the dis is to unplug knock sensor and start the engine, because of the higher voltage then required to start the car it will have a very pronounced misfire, but if the dis is faulty this option could kill it totally
I had hoped that changing the spark plugs might give me a clue about where my misfire was and how many cylinders were affected but sadly I could see no real difference between them as I took them out.
Won`t make one iota of difference if any of the leads are donald. As suggested, try pulling one lead at a time
I had hoped that the spark plug/s from the non-firing cyclinder/s might reveal the culprit/s.
Not if the misfire has been only recent
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TheBoy

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Re: Misfire Diagnosis
« Reply #21 on: 19 July 2011, 22:32:59 »
If its hunting at idle, sounds like it is, are there any air leaks?

Does it misfire when cruising at motorway speeds? Does it accelerate as expected?
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Re: Misfire Diagnosis
« Reply #22 on: 20 July 2011, 12:22:50 »
I,ve had a similar prob.(post /rotten egg smell).
First started to change plug leads and No 4 broke away from plug holder ,it had been failing for sometime as the core was burnt away although outer looked okay.Anyway while i was in there I changed the dis pack and hbv and new plugs /leads.
I did that as I think I have left plenty of skin and blood in there as didn't want take apart again (who needs smart water).Any way mis has gone ,definate plug lead U/S ,dis pack maybe okay,hbv just incase.next check cats and fit new Exh.
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Alex W

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Re: Misfire Diagnosis
« Reply #23 on: 21 July 2011, 18:39:27 »
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If its hunting at idle, sounds like it is, are there any air leaks?

Does it misfire when cruising at motorway speeds? Does it accelerate as expected?

It misfires at all speeds, especially bad around 50 mph, less noticeable above and below that. Poor acceleration.

As a mentioned on another thread ("running on 5 a day")on changing the spark plugs I noted that the front passenger side plug well had previously at some time had a couple of inches of water in it. The top of the spark plug was very rusty and the bottom couple of inches of the plug lead were covered in rust residue. No actual water was present but I now suspect that the plug lead has been damaged by this water ingress and hence my misfire.

There is no obvious sign of how the water got in there but it is near to the thermostat and a coolant pipe runs along the plenum edge above the cam cover gasket.
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TheBoy

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Re: Misfire Diagnosis
« Reply #24 on: 21 July 2011, 18:45:28 »
No2 plug :o, thats an unusual one to see wet. Only possible way in is from above.

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Alex W

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Re: Misfire Diagnosis
« Reply #25 on: 21 July 2011, 20:12:40 »
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No2 plug :o, thats an unusual one to see wet. Only possible way in is from above.

Front cylinder on passenger side needs Spark lead No 2?
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Alex W

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Re: Misfire Diagnosis
« Reply #26 on: 21 July 2011, 20:30:11 »
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Correct - misfires on the older engines are not detected, so HT issues often result in misfires, which will not flag codes.


Does it hunt at idle?

I'm not sure what "hunt at idle" means,  but the revs are not steady at idle, constantly going up and down, you can feel the car vibrate from the driver seat. Sometimes the revs drop down and you think its going to stop but then it picks up again.
Have you checked for vac leaks :question

I fixed a split plenum breather pipe but can't see any obvious vac leaks. Is there a way of checking for such leaks apart from listening for a hissing sound?
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Alex W

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Re: Misfire Diagnosis
« Reply #27 on: 23 July 2011, 13:10:46 »
Went to change spark lead No.2 today then lead 6 just fell off the diff pack revealing corroded terminal and lead end.

I decided I must get the dis pack out for a proper inspection and after an epic struggle I have found the culprit. The Dis Pack is split just like in the photos on the maintenance guide.

Hopefully replacing this and lead 6 will finally solve my misfire problem.
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Alex W

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Re: Misfire Diagnosis
« Reply #28 on: 23 July 2011, 15:05:55 »
I just wanted to add 'Thank You' to everyone that contributed to helping me sort this out.
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TheBoy

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Re: Misfire Diagnosis
« Reply #29 on: 24 July 2011, 18:17:53 »
Sounds like you have found the problem :y

I'm still concerned about that 19, see what happens a week or so after the DIS is fixed, and let us know :y
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