I have a 1967 ranger 250 with a 352 fe. just finished rebuilding. new everything - plugs, wires, ignition, distributor assembly, rings, carbeurator (factory set) ect... My #2 cylinder is missing at idle but fires sometimes at higher rpms.I haven't tested compression but I have new rings and was very tight when installed, plug is sparking strong when unscrewed out of head. what could it be?

 

I would replace the plug first, I have had new plugs that would not spark under the pressure in the cylinder. Try a dist cap off a running engine, they can have a crack that is about invisible, but causes problems. Welcome!!

 

Check for unburnt fuel residue on the plug. It could be intake vavle related.

 

yes, there is unburnt residue on the plug when i checked it. when I take the valve cover off and observe while the engine is on, all rocker arms appear to be operating properly so valves must be opening and closing when they are supposed to?? when I rebuilt the engine, I lapped all of the valves with a grinding compound and they seemed to seal pretty good but I'm an amateur so I don't know. Tonight I am going to switch plugs with a cylinder that is firing and see what happens.

 

So you've got fuel into the cyclinder, which is good.

Next think I'd do is a compression check on that cylinder.

 

I always check the easy stuff first. The spark plug is a likely culprtit. If you dropped it on the floor while installing it could have a crack in the insulator. The spark reacts a lot differently under cylinder pressure than when it tie out. Another thing that is a remote possibility is the pushrods. Ford sometimes used different lengths to adjust the valves during assembly. They should always go back in the same position. And if you just lapped in the valves into seats that are already receded without checking installed height on the stems then you may have a valve that is not fully seating. So a compression test on the hole and see what it has relative to the others.

 

Yeah, trade plugs with a plug from a known good cylinder, then do the same with the spark plug wire. You of course have to switch it as the distributor as well as the plugs.

 

ya, good suggestions. I will try them all tonight when I get off work. I appreciate all the advice. will work on the engine tonight and post the results tomorrow morning for yall to review.

 

Well fellas, the spark plug is good, the spark plug wire is good and the compression is good. The compression for all cylinders is as follows :
#1 = 135
#2 = 135
#3 = 125
#4 = 145
#5 = 130
#6 = 135
#7 = 140
#8 = 140

I took off the valve cover again and all lifters including #2 seem to be working fine but I can't eyeball thousansandths of an inch differences but they are all moving. When I tore down the engine, some of the pushrods (about 8) were bent so I replaced the bent ones. Some of the ***** at the ends of the ones that I reused seemed to be a little worn and could have possibly been shorter by a couple thousandths of an inch but generally were in good condition. The only thing that I didn't touch on the engine when I rebuilt was the cam and the lifters. Could a lifter on #2 have collapsed just a little and is not letting enough gas (I think that it is getting some because of a little residue on plug when I pulled it) into cylinder or perhaps a cam lobe worn. I assume that the cylinder is getting fire due to the fact that the plug is good , wire is good, and it shocked the hell out of me when i tried to pull off plug when running. When the engine is running, I take the #2 plug wire on and off at the distributor and can hear no difference in engine tempo so it is missing and when I go to plug it back in, to the distributor it i can see and hear sparks before it is plugged all the way in. When I pulled all of the plugs to test compression, the plugs all had a little black residue on them, just a little. Also there is some black smoke coming out of my exhaust (just a little) when I rev the engine - unburnt gas from #2 cylinder? Is the mixture too rich? If it is, do I turn the 2 mixture adjustment screws clockwise or counter clockwise to adjust (lean out)? Please give advice. Thanks in advance.

 

I just wanted to add - the #2 cylinder in not just missing, it is completely dead

 

Black smoke indicates an overly rich mixture, so turn the mixture screws in a 1/4turn at time untill you get the right mix.

As for the dead cylinder? The only thing I can suggest is that perhaps the plug isn't getting a very good ground when screwed into the head. Did you have the heads done? Perhaps someone stripped out the threads for the plug and used a helicoil or something?

You've got compression, you've got fuel so that only leaves spark. Have you tried posting this problem in the FE forum. There's probably a few guys/gals there that could diagnose this with one hand tied behing their backs.

 

nobody mentioned a possible vacuum leak had a dead cylinder once after a rebuild drove me nutts trying to figure it out it was on a GM product it had a vacuum port on one of the runners on the intake that little leak would not let the cylinder fire at an idle since you have no problem pulling the valve cover pull it off & crank the engine then spray some kind of lubricant [wd-40] all around the gasket and see if the cylinder starts firing as long as you are spraying the lube if there is a leak the lube will temporaly seal the leak if this it pull that 80# intake off & put new gaskets on this is how i found a leak on my harley.

 

come get some has a good point too. It would make sense, sorta... but wouldnt it arc from somewhere?? Spark is some pesky stuff. It gets everywhere you let it, and he said he was getting spark when he pulled the wire. XLT is headed in the right direction, I think. But comegetsome's idea is a very good one, and something that would stump the best of us!

 

well fellas, I think that I have diagnosed the problem. I took off the valve cover and observed the rocker arm assembly very carefully for a few minutes. The rocker arm on the #2 intake doesn't seem to be moving up and down as high as the rest of the rockers. I traded the pushrods out with a good working cylinder and still looks the same. I also put my finger on it while it was moving up and down and I could definitely tell a difference in feel. I think that I am going to have to get a new cam. What do yall think? I don't want to pull the engine again. Is it possible to install a cam without pulling engine. Also, what special tools do I need to dial it in. I am not replacing the bearings, just the cam.

 

you shouldnt have to dial it in. It is possible to do it in the truck, but you will have to remove the radiator.