Ok I am just about at the end of my rope. I bought a 68 F250 4x4 390cid 4V. When I bought the truck the engine was missing. I figured a good tune up and I'd be good. Well I ran the problem down to a bad/burnt valve. I pulled the heads and there was the problem. #4 cyl had a bent exhaust valve. I took the heads in to get re-conditioned and the guy did a great job so please don't second guess his work. The heads are perfect. He even painted them Ford blue for me. I put the painted heads back on, lit the engine and got it warmed up. I felt a slight miss. Damn! I thought I had this fixed. I did a cyl power balance test and #4 was my dead hole again. I did a comp. test and all cyls were pretty close. All were around 120-125psi. Let me add I was a Master Certified Mechanic for quite some time so I have been thru all the basics. Its not a bad plug or wire or broken spring. Mechanically the engine isn't in bad shape. I was leaning towards a vacuum leak because I have heard these FE's like to leak around the intake manifold. All gaskets are new! There is a vacuum port on the intake runner that goes to the brake booster. I pulled the hose off the booster and plugged it just to be sure there's not a booster leak. Still missing! I even get a pop in the exhaust sometimes too. I didn't spray anything or use LP around the intake manifold yet but that's next on my list. Am I missing something here? I'm ready to push this thing off a cliff and then jump myself. Please talk me off the cliff!

 

I'm not an FE guy, but I had a similar problem with a untraceable misfire. MY problem turned out to be a collapsed valve spring. Not saying that's yours, but I would tend to think it is something mechanical like that if all the other systems are working properly.

Also, we have a dedicated FE forum farther down the main page. You might post there as well.

 

You also need to verify if the cam, Lifter and push rod for that cylinder is working correctly. Once that is done start looking at the Distributor, Cap, Wires and Plugs. These are the only things that will cause your miss if you already did the heads. One question on your head rebuild, did he install hardened exhaust valve seats?

 

Compression test shows that they are all the same? So, the valve job is okay. You mention pop in the exhaust. That tends to make me think a valve is hanging open or it is cross firing plug wires while the exhaust valve is open.

I would recomfirm all valvetrain is operating properly, then check wires/plugs.

 

Thanks for the help guys. I was re-checking everything today and was really leaning towards a vacuum leak. I re-torqued the intake manifold and did not see anything wrong. I heard these intake manifolds like to suck oil from the underside. I decided to take it out for a spin and noticed the cloud I was leaving behind the truck. It wasn't smoking in the garage. Now I am really thinking I'm sucking oil. The truck has dual exhaust so when I got back the inside of the tailpipe is coated in oil. I pulled all the plugs, did a compression test. 135-145psi. Not bad right? When I pulled 2 of the plugs I noticed 2 were a little oil fouled. I did a cylinder leakdown test and it seems my engine is just tired. The 2 cylinders that were fouling the plugs have about 50% blowby. When I pulled the pcv valve out with air going into the cylinder you can feel the air coming out through the crankcase. Yep all this hard work for nothing. Time to pull the engine and have it rebuilt. The wife isn't going to be happy about this!

 

Most times when you put fresh (read:tight) heads back on an engine with old,worn,weak,etc. rings they can't handle it. The rings that is. The new-found compression from the tight heads "blows the rings out of it". Not literally....that's an old saying. Sometimes a person can get away with it but the odds are against it. As you found out.

 

Sorry to hear about your FE troubles. They are great but very stubborn engines when it comes to many aspects. Are you going to get the parts machined and build it up yourself, or are you leaving it all to a machine shop?

 

Again thanks for all the posts. I'm gonna pull the engine and go thru it top to bottom. The reason I (we) bought this truck and so my son and I could have a project to work on together. It'll be good learning experience.

 

When you pull the engine do not be surprised when you find out its a 360 and not a 390. There was never a 390 installed into a 1967 to 1972 F250 4x4.

 

To be accurate what you *should* say is that there were no *production* 1967 to 1972 F250 trucks with a 390. If one had the money and inclination they could order the truck with any engine available in any Ford vehicle. So it could be entirely possible for a truck to have a 390, 428, or even a 427. Ford used to be a customer oriented company.

 

Ford did NOT install 390 engines with 4WD! 427/428's were only installed in cars.

1965/76: Only available V8's with 4WD:

1965/67 F100/250 4WD: 352 2V / 1968/76 F100/250 4WD: 360 2V

And...on sale day, 352/360's magically become 390's!

352 B&S: 4.00" x 3.50" / 360 B&S: 4.05" x 3.50" / 390 B&S: 4.05" x 3.78"

 

In the 60s and 70s Ford did whatever the customer ordered. My Dad had a custom ordered 1969 F250 4X4 with 390 4bbl auto. It cost him something like $200 bucks extra. If I hadn't have wrecked the thing in '74 I'd give you the codes off of it.
Ford also "never" made a 1962 Galaxie 406FE Tri-power with a bench seat and a 3-on-the-tree and overdrive. I owned it and it is here in Tucson after being fully restored by Tim Warfield. Damned cool car and I wish that I'd never sold it.
Mercury "never" installed a 427 Dual-Quad in a '67 Cougar either. But a friend of mine ordered one Custom Factory Made.
My girlfriend had a '66 Ford Country Squire with a 427 4bbl. Custom ordered from the factory. To make that story even more incredible she bought the car from an old lady for $300 in 1977. When Jackie went into the NAPA to get an air filter in 1978 the sales man, a friend of mine named Keith, went out and opened the hood to see what engine. He thought it was a 390 and pulled the part for her. But the air filter didn't fit the housing. So he took a better look and saw the crossbolts. Jackie was really pleased to sell the car for $1000... Ugh. Another one that I missed out on. Keith put it into his "76 4X4. Another guy from down in Camp Verde ordered a F-600 Dump Truck with a *BOSS* 429! I knew him and the guy who bought the engine in 1994. A guy over in Wilcox custom ordered his F-600 Dump truck with a 427. Custom from the factory.
Another words there are a *LOT* of non standard yet factory assembled vehicles out there.

Your statement makes me wonder just how long you actually worked for Ford. If you'd been there before the late 70's then you'd know better.
Ford did *not* install the 390 in any **PRODUCTION** 4x4. That much is true. Ford didn't install a lot of things in production cars and trucks but Custom Orders made for some damned interesting vehicles.

 

Ford supposedly never made these either, but they do exist as I've seen them in person.

A pal of mine owns two 1963 Ford Country Squires, one has a 406, the other a 427. Both have T-10 4 speeds, swing-away steering columns, consoles and bucket seats.

He also owns a 1971 LTD convertible 429 with 3 speed on the tree. It was assembled at the Louisville KY assembly plant for a Ford executives wife that couldn't drive an A/T.

 

It would be really cool if we could still special order vehicles like that. I would have got a 4x4 ranger with an eco-boost motor.