Hello FTE!
I live on a cattle ranch in Montana. We are a die hard Ford ranch! We bought a 1986 F350 when I was just a kid and put a round bale bed on the back to feed cows. We've had the truck about 15 years. We have rebuilt the engine once since we got it. It spends most of its time in 1st and 2nd gear (its a manual truck) and mostly low RPM driving. We have gone through 3 carbs (That was the mechanics solutions to the problems) over the life of the truck. It will idle fine, throttle response will be great, and it will start fine, then suddenly, after about a month of operating fine, it will idle like a cammed 460, sputter if you drive it somewhat aggressively, and won't start very well at all. It almost acts like a timing issue, but Ive checked that every time this happens, and thats never the case. I believe all of the emissions stuff was capped off and disconnected when we got the truck. Ive looked for vacuum leaks and never find any. When this happens, it fouls plugs as well. The truck came with a Holley, we ran that one for a while, rebuilt it, ran it for about 2 years, went to an edelbrock, that lasted 1 year, then went back to a holley. The truck doesn't see much use anymore as it has been replaced by a 97 power stroke. But when we do use it, the symptoms sometimes return.
Any thoughts on what could be causing this? could it just be the fact that 460 is not really designed to be lugged around the hills day in and day out?
Thanks!

 

Any similar problems before the rebuild? Sure it's a stock cam?

You could be running way too rich for a stock motor with those carbs unless they are stock replacements.

Aside from a vacuum leak you haven't found, I'd say your dumping too much fuel in. Running low RPM's all the time doesn't help either but probably isn't the main reason.

My uncle's '87 stock 460 and stock carb runs great still.

 

Yeah it did the same thing before the rebuild. I have no way to verify that it has a stock cam in it, but when its running normally, it acts just like every other 80s 460 I've been around. The carbs have all been stock replacements. The truck was some type of high performance engine, according to the P.O. and belonged to some texas police department before he owned it (there was a sticker in the window for the longest time that somewhat verified that).. I don't think that changes anything. It has headers on it, but thats all I could see that was out of the ordinary.

 

Your'e in a whole different ball game now. There is no telling what the police would have had done to it to crank it up unless you find the original builder. You may be forced to tear it down again to find out?

What kind of fuel are you running? What altitude are you at?

We don't run 87 octane in our '87. E10 89 octane is the minimum we run in it, but it always runs a little better with some premium in it.

 

We are at about 4,230 ft.. We buy gas in bulk, and I believe its just minimum, 87 octane. The guy who did our machine work didn't say anything was different than stock, but he also wast looking for that, and it didn't need much machine work at all. What was the compression ratio of these engines factory? (as you stated, ours could be different but just for my info )

 

Stock would be around 8.5:1.

Have you ever tried premium fuel when it was running ok?

Are you getting detonation? I would look into the specs of your motor. I would guess you have a bigger cam and possibly higher CR. You may be able to tweak your carb to make it work.

 

Not a chance 8.5:1.
7.5:1 -if lucky- stock.

Next time it acts up, open the hood and put your hand on the coil.
Is it really hot or just warm?

If it sets for a couple of hours will it start right up and seem okay?

 

We have never put any premium fuel through it, but will try that next time we fill it up, The truck rarely gets used now, and I'm looking into taking the bale bed off and finding a box for it and making it a regular truck instead of a ranch rig this summer. Thats why I'm trying to figure out this issue. Ive never heard it ping so I don't think detonation is an issue. Sometimes when It acts up, I've had luck taking it out on the road and driving it like I stole it for about 10 minutes, The idle will sometimes become normal again, and it won't stumble when you hit the gas. I don't know if that is just purely by chance or what… Next time it happens I will check the coil. What would a hot/warm coil indicate? If it sits for a while, sometimes, rarely, it will start behaving normally again. Generally what we end up doing is (Keep in mind, My Dad was the daily driver for this rig back when it was used daily, and his mentality has always been: If it ain't broke, don't fix it, so if it would start, he would drive it, against my recommendation!) keep driving it until it fouled the plugs so bad that it need a tune up, (and we would also mess with the carb too) or until it just went away. My dad could change his driving habits to keep it stumbling along at an idle. If you get it off idle a little bit, it stays running fairly easily.

 

Sure 'driving it like you stole it' will burn some off the carbon of the plugs and it might run better after that.
You say your dad won't fix it unless it's broken.
How long has it been since it's had a tuneup? (rotor, cap, wires, plugs, filters)

You have changed the carburetor a few times and it doesn't seem to help in the long run.
As long as it's getting used (some) and the fuel is good the carb shouldn't be an issue.
Prolonged idling is an issue, maybe propane would be a better choice?


If the coil windings are breaking down the coil will be hot and the spark will be weak.
A coil will wear out, and the symptoms fit.

 

That would make sense. The carb replacements were all local mechanic shop solutions, I realize that they were not actually fixing anything haha. How difficult is it to run propane? Would you have to change CR or heads? Mileage might be a bit more economical as well. I might just throw a coil on it next time I'm home (probably about a week) to see if that helps anything.

 

Well you say it is a farm truck and you would have the bed off.
This sort of thing used to be pretty common for farm & fleet trucks that didn't have to travel beyond their fill up range.
(and before propane got expensive)

I have not run propane but know that propane burns real clean and increased compression is optimal due to the high octane equivalent.
Ignition timing needs to be adjusted.

I threw it out there because it seems to fit the use and your area of the country.
People say their plugs are always spotless and oil is too.

Maybe not worth it for a secondary vehicle that is no longer used much.
Unless you can find a second hand system from someone who's truck is trashed.

I think most important is to do some actual diagnosis (instead of just part swapping) when you get to the truck.

 

X2 on the diagnosis.

I had no idea they ran compression that low, my bad.

If you are going to make it more of a streetable truck, it would be a good idea to do the so called 6liter tuneup and go with the MSD or accel ignition coil, cap and rotor. Make sure to gap the plugs! I stretched mine out to .055"

 

Well, Ford would tell you compression is 8:1, but actual measurments would say otherwise.

There's nothing wrong with the proper Duraspark coil.
You can open the gaps up some.
I wouldn't go .055, from the called for .044.
Opening them up too far just cause the voltage to find another path to ground.
Puts more strain on all the other ignition components. (wires, cap, rotor)

A bigger gap is just a cover for poor mixture or chamber design.

 

Hey guys I went up to MT this weekend, but unfortunately didn't have time (or a battery) to do any diagnostic work on the truck. Got to talking with Dad about it, and decided that we are most likely going to do a cummins swap on it. We have a 2001 Dodge 24v (Its falling apart around itself, and has been since about year 2 of owning it) and since its a Dodge, it steers like a tractor, Has the undersized rear brakes, goes through track bars every 35,000 miles and needs aligned about as often, and the interior is falling to pieces. Ive got a spare zf5 speed sitting in the shop, So the clear thing to do is put it in the '86'. Thanks for your help though!

 

Mounts, adapter and pump are not going to be cheap.

But it should be nice to have that engine in your ranch truck.
There is an engine swap board on this forum.
https://www.ford-trucks.com/forums/forum136/
I'm sure you will get a lot of good advice there.

Best of luck!