Can a exhaust leak by the manifold cause a misfire?

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Matty2148
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by Matty2148 »

Is this missfire rythmic? from reading this thread I`m getting the impression it is, if its the same cylinder missing all the time regardless of plugs, leads etc I`d be more inclined to do a compression test on all cylinders and check valve clearences, if they are equal or close Id then move to dizzy cap swap and rotor arm. Thats if its a rythmic missfire, your mechanic mate says it doesn`t sound like the valve clearences need doing, that means nowt (no disrespect to him) , doing the valves will take me the whole of 30-40 mins maybe 1hr if the rocker cover is a bugger or you have air filters to shift etc.
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by PeterG2.8 »

Valve clearances especially if you're not running an unleaded head with hardened seats, check them, can't understand why people dodge this issue. The number of engines I've done clearances on you wouldn't believe and all had tight exhaust valves, some with no clearance at all. Valve seat recession is real!!!! :drama:
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by renaulthater »

Tappets,...........
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by jamezz666 »

a quick short update as im just working on it now and i've checked all clearances and there fine with movement in each one and on the feeler gauge 0.25mm for the exhaust and 0.20 for the inlet all fine no problem there and i tried 2 othe dizzy caps and rotor arms and still nothing and yes its rythmic so any idea guys?
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by nigecapri »

Do the 'Remove plug lead' check again.
If it's rhythmic then it's usually HT related. Leave each lead off for half a minute, with the defective cylinder disabled it will go down to three cylinders but be regular. With a good cylinder disabled it will occasionally go down to two cylinders and probably stop.
If high mileage then the dizzy shaft could be loose allowing the rotor arm to wobble a bit, something I've never experienced though.
Fit known good HT leads & cap - do you know anyone with a sound-running pinto to swap from?
Whenever removing HT leads always twist the rubber cap a fraction to release it from the plug or dizzy cap then pull the rubber cap, not the lead.

First job though is to sort the exhaust, it could be that you're getting secondary combustion down the exhaust from unburnt fuel mixing with air making a similar sound to the engine missing :!:
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by stevemarl »

If high mileage then the dizzy shaft could be loose allowing the rotor arm to wobble a bit,
More importantly it will allow the cam to wobble - making dwell & timing inaccurate.
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by rich_jc »

I do hate to repeat myself, but have you removed and checked the carb idle jet?

However if it is rhythmic, I would suggest it is an ignition problem, and you should persevere with the pulling off of plug leads to see which has the least effect.

As Nige said, make sure you know the other caps you are trying are good, don't just assume they are.

Rich
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by jamezz666 »

i'll have ago with the leads again today once its stopped raining and the dizzy is only 2 months old so the shaft will be ok and I don't know anyone close to where I live with a pinto :/ and my other to dizzy caps what I tried one is an old one off my points dizzy and the other cap I got is new and its the same so I ruled the cap out. so im guessing its most likely the leads. and yes I checked the idle jet I did clean the carb out yesterday and theres no difference so im guessing once I got some more money i'l have to buy some leads as im stunned for money at the minute as I cant even afford my tax until 2 weeks time.
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by Msteve »

any luck with this?
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by jamezz666 »

no im afraid it has bugged me as I cant be bothered now I changed and checked everything had a couple people look at it and even sorted a 4 branch manifold so that isn't causing any problems and it isn't the old average little engine shake as a couple people who hear it running and who has taken ago even said that it has a very funny misfire so to behonest unless if I have an expert around its not going anywhere and I cant afford an expert to come out.
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by pbar »

Would it be worth saving up for a little while, then taking it to a local trusted garage, they might find the issue in a day and you would have it back all done and ready to drive. Just a thought, would be worth it if you have reached that point now, sounds like you have had a good go yourself.
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by Msteve »

did you get your valve clearances checked? maybe it's a sticky valve or the inlet valve is stuck open...
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by jamezz666 »

the chap next door to my unit hes has hes own mot work garage and he's had dozens and dozens of old fords and worked on more than I could imagen he even has a Cortina hes just fully restored and hes a friend of mine and he went over the capri and it blew hes mind so I think I either save up lots of money so it can go to a capri specialist or just leave it. and yes the valve clearances was checked and they was fine never needed any adjustment and they aren't sticking. so this is why it has blew my mind and others who have had a look and tinker. just wish there was a capri specialist close who wasn't so expensive to have a look as I could bet the green slip of my car they would have it for more than a couple of days trying to figure this one out :/
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by 340truck »

With the greatest respect - don't waste your money on a "capri specialist" - if a good Ford orientated mechanic can't suss it then it's not worth it. The pinto is a fairly simple engine, I suggest you take the head off, strip and clean it, re grind the valves in and then replace with all new gaskets. Re set clearances as part of the job. If you still have a misfire after that then get a replacement engine, max price £200 and probably less if you find the right one.
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by pbar »

Just take it to a local garage, tell them what the problem is, and/or ask for a quote to sort it, and they will book it in as a proper job. They will then look into it and either fix it for you or tell you that they can't. In which case you move on to another one and try again.

Nice and simple. How can that not be worth a try.
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Re: Can a exhaust leak by the manifold cause a misfire?

Post by Terra-Kotta »

No
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