Put a new 460 in my 78 F-250. The only problem Im having is when I put the engine under load it starts to mis fire and if I really get into it it backfires thriugh the carb. I've checked and double chacked the base timing and had it anywhere from 10-15 degrees. Ive checked the firing order as well. Ive had it at two local shops and all they have done is give me a bill and tell me to take it away they cant figure it out they want to start throwing parts at it. All the valves are sealing theres no broken or worn valvetrain parts that I can see and one of the shops verified that too. Where do I go from here? Thanks

 

it sure does sound like a timming issue,you have tried setting it from 10-15 degrees already,what type of distributor are you running,is there vacume or mechanical advance on it?

 

Or maybe your Duraspark box is dead, how did it run before you put it in?
You should replace the old timing set with a steel set.

By new you mean rebuilt or crate motor?

 

If the module was dead, the truck would not start.

The three step scenario of a failing DuraSpark ignition module.

1) Module overheats, engine dies. Module cools down, engine re-starts almost at once.

2) Module overheats, engine dies. Module cools down, engine re-starts in an hour...or so.

3) Sooner or later...usually sooner, the module overheats...burns out. Now the engine will not re-start.

Since the module only fails when it overheats, taking it to an autoparts store to be tested...usually doesn't work...unless the puppy had died altogther.

The 460 engines used thru 1978 (Passenger Cars) and thru mid-year 1979 (F100/350's & Econolines) do not use a weighted spacer.

Mid-year 1979, Ford changed the 460 engine, which now uses a weighted spacer. The harmonic balancer and flywheel are not the same as the early engines used.

This new 460 engine was a running change, so there is no serial number or production date break.

To ID which one y'all may have: The block casting number for the mid-year 1979 and later 460 engine is D9TE-6059-AB.

1968: The block casting number is C8VE-6059-AB / 1969: C9VE-6059-AB / 1970: DOVE-6059-AB.

1971 thru mid-year 1979: D1VE-6059-AB or -AB1 or -AB2.

 

Too much lifter preload can cause a misfire. Was lifter preload checked ?

 

I think the best thing to say is we need more information on the engine,there are so many variables.

 

This sounds almost exactly what my Fury does, but my Fury has a couple of flattened lobes on the cam whereas, you stated you couldn't find any worn valvetrain components...

Could a misaligned distributor cause this?

 

thats a good thought fury,I had that happen with few small block chevs,I am unsure what he means by "new 460",is it newly built,crate or just new to the truck.

 

Its a rebuilt crate from what I thought was a respected company but have had several issues with them since I bought the first engine. (that turned out to be a bust) Ill check on the casting numbers. The old engine ran like crap. It had oil shooting out the dipstick tube, the carb had taken a severe beating with a hammer(or it looked like that) it always stalled and died and smoked like a dirty dog. Im not sure about if pre load was checked or not. What would be the best way to check it my self? Its been at two different shops and both have ruled out valvetrain. Both shops double checked timing and firing order and said it was fine. The first shop set timing at 15 degrees and the 2nd set it back at 10. Both shops said they wanted to start throwing parts at it. I got a new distributor from ford dealership, and it looked identical to the old one, there was no weights in it. A friend just called and said that sence the 460 wasnt the original motor the duraspark may not be ok to use with the new engine and I may need an msd or similiar box. what do you all think? Thanks a million everybody

 

Your friend doesn't know diddly-squat! 1973/79 F100/350's were available with 460 engines. DuraSpark was introduced in 1974, and...

1976/79 F100/350's, Bronco's, Econolines and most passenger cars (excepting some 1979 LTD's and some 1977/79 vehicles sold new in CA) used the SAME DuraSpark ignition module.

The engine size...makes absolutely no difference.

This module was also used from 1980 thru the 1990's for myriad applications.

DuraSpark modules have a colored plastic square above where the wires feed out, this is an EZ way to ID them.

1U2Z12A199AA .. Ignition Module BLUE plastic square (Motorcraft DY893) / Available from Ford.

1U2Z12A199AA replaced D9VZ12A199A & D6AZ12A199A.

Fits: 1976/79 everything except some vehicles sold new in CA and 1979 LTD's with EEC.

Fits: Myriad applications from 1980 thru the 1990's.

Some 1977/79 cars/trucks sold new in CA used a module with a red plastic square (D7AZ12A199A).

But all of this jazz makes no fracatta difference as the module your truck has now (whether it's blue or red) will work just fine...as long as it isn't defective.

 

I had the same problem with my truck (78 F-250 4x4 460) several years ago. I chased my tail trying to solve it to no avail until I decided to remove the engine. I used Hooker headers for the engine swap. When I unbolted the headers during removal it turned out that the driver's side header was misdrilled causing the flange to be completely misaligned with the exhaust ports. The engine ended up in a friend's pulling truck with a different set of headers where it ran fine.

 

If all your timing valvetrain and electrical checks out then make sure you are getting enough fuel. I have had 460's fuel pumps not keep up at full throttle and cause a leanout condition.

 

Well ya get her running yet?