ford courier miss

[MTChevy]

I had a friend come to me stumped over a cyl 3 miss on a little 4 cyl in a courier. Cant be hard to diagnose right? Well, i checked spark and compared spark against the other cyl, good.

Checked compression. Within 10 psi of all other cylinders. Just rebuilt the carb. Checked points. Pulled valve cover and checked rockers and gear mesh of distributor. Vacuum advance is froze on the distributor but thats it.

What am i missing here guys? Every thing checks out but there is a dead miss on cyl 3in at idle that seems to clear up at high rpm

 

[imiceman44]

With 10 psi difference you will get a miss at idle but not at higher RPM, That is normal and to be expected.
Now to make that miss lass noticeable you could put a hotter spark plug in that cylinder.
I did that to a 2.0 litre peugeot engine that had 1 &4 higher than 2&3 so I put the hotter spark plugs in the middles cyl and it smoothed out.
I had 20 psi difference, and the advise I got from my mechanic who said the engine is done but you can squeeze another year out of it like this.
Sure did, 2 years later I was still driving it.

I had a friend come to me stumped over a cyl 3 miss on a little 4 cyl in a courier. Cant be hard to diagnose right? Well, i checked spark and compared spark against the other cyl, good.

Checked compression. Within 10 psi of all other cylinders. Just rebuilt the carb. Checked points. Pulled valve cover and checked rockers and gear mesh of distributor. Vacuum advance is froze on the distributor but thats it.

What am i missing here guys? Every thing checks out but there is a dead miss on cyl 3in at idle that seems to clear up at high rpm

 

[diesel4me]

You might have a vaccuum leak or intake gasket sucking air that affects only #3 cylinder too...it'll lean that one out to the point it wont fire at idle,but at higher speeds it will be much less noticeable....sometimes a intake valve gets crud build up under its head and wont let enough air/fuel mix get into one cylinder too,or a loss of valve lift from a cam lobe worn down or inncorrect valve lash can do it too...on injected engines a faulty injector can cause a cylinder to seem "dead" too,especially at idle.............................................I assume you checked the distributor cap for cracks or carbon tracking,they can cause some weird symptoms like this sometimes too--so can a faulty or cracked coil....or plug wire..