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my Mk4 fiesta 1.3i keeps on misfiring during tick-over. The cylinder nearest the gearbox doesn't do anything, when i remove the spark plug it doesn't affect the tick-over. I have removed the head and checked the cylinder bore this was O.K. reground the valves. then done a compression test (pumped compressed air into the sparkplug port and checked the inlet and outlet ports for leaks) which was O.K. checked the spark O.K. I can't think of anything else it might be any ideas?
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you have gone a long way to check out something that may be as simple as a duff plug.if only one cylinder is not firing as you said would be down to HT fault which I would go for.
check out the ht lead from.I am not sure if it has a distributer but if it has could be the lead is shorting out at some point.it isn`t uncommon and if that wont cure work back from cap I doubt that it will as 3 cylinders are fine tend to think cap rotor or ht lead.could be wrong but thats the way to go
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thanks for the reply, it hasn't got a distributor it is all electronic. I forgot to mention that. also I have tried swapping the pluggs from different cylinders which doesn't solve the problem. there is definately a spark to that cylinder though.
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sorry I did not read properly.a compression test is done through the sparkplug hole.pumping air into the cylinder is done or at least used to be done for adjusting valve clearances ie just as a valve opened the other was adjusted.I would think your problem would be fuel injector as you have a spark at plug but no fuel.does it run better as it warms up?
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As it is only at idle I would suspect either a fouled injector or an air leak to that cylinder. Cant recall from mrmory but where does the vacuum pipe for the servo (or any other vacuum pipe)connect to the manifold. If it is adjacent to the missing cylinder unplug the pipe from the servo and plug it to see if that helps.
Andrew
Simplicate and add lightness!!
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thanks for the info, there was a sensor connected to the inlet manifold on that cylinder, I blocked it and it still didn't solve the problem. I don't think it is the injector because it is a single point fuel injection system. I could get the engine to run on just that cylinder removing the sparks plugs to the other 3 but it required a lot more throttle than on any of the other cylinders. Do you think I ought to remove the inlet manfold and check the gasket, other than that what else could it be?
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sorry forgot to mention that the misfires is always there no matter how warm the car is
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Ahh single point!! Could be inlet manifold/gasket prob. Whip off the rocker cover and check the amount of movement of each valve as you turn the engine over with a spanner on the crankshaft nut. You may find that the camshaft has worn on that cylinder and the valves(s) dont move enough. This will cause a prob at idle but not at higher engine speed. Also, silly question are the valve clearances correct and adjusted in the correct order?
From left to right facing the engine Ex In Ex In In Ex In Ex
Inlet .2mm Exh .3mm
Andrew
Simplicate and add lightness!!
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thanks for the advice, I will try the valve movement test, I suppose that cylinder will have the most wear because it is furthest away from the oil pump. also how much oil should be coming out of the rockers when the engine is running because it is only a small trickle from each one. on other engines I have worked on it has been a lot more. could the oil pump be knackered which caused the wear in the first place.
I will also check the valve clearances but I think I have done them as you describe.
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checked the valve lift it was O.K. on all the cylinders it was around 8mm on all of the valves. the other thing i did was to remove the throttle posistion sensor and the tick-over plunger thing from the throttle body. with these removed the car still had quite a high tick-over. would this indicate a leak on the inlet manifold?
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i have run the car now for a couple of weeks the misfire is still there but now the fuel consumption seems to be a lot higher and the exhaust has lots of carbon around, is it possible this could be some kind of electrical sensor fault, is it worth me getting a fault code reader as these are only £20 does anyone know if they actually work?
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