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Topic: Misfire - running unevenly (Read 614 times) |
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TomP
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Misfire - running unevenly
« on: Apr 2nd, 2011, 8:14pm » |
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Scorpio 2.9 12v Estate (1996 P Reg) 103k miles
My beloved Scorpio is starting to run a little roughly. Usually slighlty worse at low to mid speed, but seems to be a bit smoother when up to around 70mph.
Looking at previous posts and having had a Mk3 Granada previously with a similar problem, I'm thinking it could be the Ignition Leads. I changed the plugs, distributor cap and rotor arm about 2 years ago.
Surprised how much I was quoted at Halfords for the leads (approx £75) although they didn't have them in stock.
Any suggestions what else is most likley to be the problem before I start seeking a set of leads from Ford or local motor shop?
Many thanks.
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gozz
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Re: Misfire - running unevenly
« Reply #1 on: Apr 2nd, 2011, 9:11pm » |
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Tom.
You need to locate which cylinder is not firing,presumably it misses when idling ?
pull each lead off in turn and note the change in running,best to loosen them first to avoid a jolt.
Halfords are obviously not interested in your custom  they are a joke.
If you remove the plugs it should be easy to see the odd one out by it's colour.Should you decide to replace the leads get them from a motor factor,or if you trace the problem to one lead,just replace that.
The 12v injectors open in complete banks,so unless you have a dodgy injector it is unlikely to be electrical in that case.There is always a slim chance of a leaking valve,a compression check would show that up.
GOZZ.
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TomP
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Re: Misfire - running unevenly
« Reply #2 on: Apr 2nd, 2011, 9:38pm » |
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Very many thanks for your reply.
When idling, the rev counter does fluctuate betwwen 500 and 1000.
Sorry, dumb question, but are you saying that by removing the plugs and finding the one that looks a different colour, that will tell me which lead is likely to dodgy? Or does it mean the plug needs changing?
I'll try removing the leads in turn in the morning. What do I do, keep taking one more off each time, or take one off, then put back before taking the next off? What will be the sign in the change to the running, when I find the problem lead?
Really appreciate your advice. Thanks.
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Snoopy
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Re: Misfire - running unevenly
« Reply #3 on: Apr 3rd, 2011, 7:31am » |
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Also make sure the top of the coil on the inner nearside wing is spotlessly clean, I always cleaned mine on a regular basis, and make sure the LONG HT lead that goes to the top of the distributor is well away from other metal objects. You could also have a look at the rotor arm inside the distributor, just like in the early days of cars.
The 12v does use rather old technology in its electrical ignition system system but it has stood the test of time and is usually very trouble free. Good luck.
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TomP
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Re: Misfire - running unevenly
« Reply #4 on: Apr 3rd, 2011, 8:16am » |
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Thank you Snoopy.
What should I use to clean the top of the coil?
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gozz
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Re: Misfire - running unevenly
« Reply #5 on: Apr 3rd, 2011, 3:57pm » |
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One lead at a time Tom and listen for no change in engine note,when you pull one off that makes no difference,that is the faulty one.
If you have as you state,a big idling rev fluctuation,that is not a faulty cylinder,it could be an air leak on the intake side or a very ropey idle air control valve,try pinching all the vacuum pipes one at a time and see if you can locate it,they are all those little rubber tubes that connect various units to the inlet side,look carefully under the plenum chamber(big aluminium thing)at the front of the engine,there is a tube there that is known to come loose,the gearbox shift is assisted by vacuum,if the diaphragm in the module ruptures it will draw ATF into the engine,but you usually get exhaust smoke when that happens.In answer to your question to Snoopy,just a piece of cloth.
Good luck
GOZZ.
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