Missfire. Possible vacuum caused.

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Joined: Sat Nov 26, 2016 1:58 pm
Car(s): Ford Capri 2.0 Ghia, Mk2, Pinto

Missfire. Possible vacuum caused.

Postby nik1 » Mon Oct 09, 2017 11:05 am


The vacuum hose kept jumping out of the breather rubber and causing real rough running. I replaced the breather rubber and now the hose is nice and snug inside it, but I still had some rough missfire and running especially at low revs. I checked my spark plugs and they had carbon fauling, which happens when the engine is running rich (which was caused by the driving with the vacuum hose not in the breather rubber assembly? ). I cleaned out the spark plugs the best I could with a file as they are the 4 electrode ones and I don't want to replace them yet $$. After letting the engine warmup and appeared to run smooth again and it was fine on a test ride. I went on a 30 mile drive and on the way back it started to do the missfire while on the motorway. To describe the missfire, it kind of feels like it needs more gas than usual to take off for example (power loss feel) and engine is joking and bumping, and bumping less if I go to high revs ~4k. I can't see any air leaks, but I haven't started taking anything apart. Could it be that it just needs new spark plugs. I will post a picture of how "well" I cleaned them and will check if they have gotten carbon fouled again.

Pinto 2L, 32/36 DGAV. Let me know if you need more info :)

Paul G
Posts: 1035
Joined: Fri Jul 03, 2015 5:21 pm
Car(s): MK 3 3.0S needing restoration, 2.0S, 1.6 Laser (nearly ready), Fiesta mK2 pop plus, Skoda Octavia VRS, Rover SD1 Vitesse.
Location: High Wycombe

Re: Missfire. Possible vacuum caused.

Postby Paul G » Mon Oct 09, 2017 12:04 pm

It could be many things causing this problem. Are all your other vacuum hoses connected correctly and in good condition?

You say the car is running rich which could just be a mixture problem or the float level in the float chamber. Also is the automatic choke turning off properly (flaps open when warm)? To roughly set the idle mixture screw the mixture screw in slowly until the engine revs begin to slow down then slowly out again just until it idles smoothly.

I would also check your points gap and ignition timing.

If it's not the carb the cutting out after a long run could be the coil overheating and breaking down - or your valve clearances are too tight.

I would also say just stick a set of standard cheap NGK APR6FS plugs in for now and see how you get on with them.

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