I have a 1986 F250 XL 4x4 SuperCab, carbureted 460, four speed, 8,800 GVWR, 3.55 axles, dual fuel tanks, manufactured 9-86.

I've had problems with the truck quitting, restarting, quitting again. The problem was intermittent, gave me fits. At first I thought it was ignition, and mistakenly swapping in a bad ignition module from my '77 F250 (1-year old Neihoff, and good when I parked the rig to change engines) didn't help my troubleshooting.

But a timing light will confirm when there's spark, and a pressure gauge will confirm when fuel is being pumped to the carburetor. I've already blocked the return line coming out of the side of the little fuel pressure regulator ahead of the carburetor, thanks to advice from more than one source.

Finally got a 0-15 psi gauge plumbed up. I was showing 5-1/2 to 5-3/4 psi. Switching tanks didn't have any effect. Then as I let it idle way down, the pressure faltered a bit. It died and I restarted; pressure went to zero indicated. Must have been something there, as it was still running, but the gauge said zero. Several shutdowns and starts eventually resulted in normal pressure again.

The guy at the parts house said he showed both mechanical and electrical fuel pumps for this truck. Mine has the electrical pump, sort of an angular thing, located at the front of the first fuel tank.

Since the pump is about 90 bucks, even at Schuck's, I guess I'm asking for someone with experience to give me some odds: What are the chances I have an intermittent circuit to the pump? What are the chances the pump is dying? For what it's worth, the truck did a lot of sitting, only occasionally being started, before I bought it (clever me, I bought it a week before Hurricane Katrina gave us $3 gas).

I'll change out the pump, if that's what it needs. I just like to be pretty sure what the problem is, before I throw money at it (after all, I'm not a liberal politician, and it's MY money I'm throwing).

One other consideration: Sometimes, only the factory part will work ('86 Civic Si thermostat, '88 GM fuel pump, as examples). Do I need to worry about my source, if I buy a new pump?

Minor note: There is some leakage from the Holley carb. Some friends have advised me to just get one of those 600 cfm Edelbrock (Carter) carburetors that go on sale at Schuck's. I bought one for my '77 and it ran fine until I blew the head gasket on my 351M (and I'm sure it will run fine when we get the used 400 installed). In Skagit County, I don't have to worry about emissions testing or any such inspection. I want reliability, but again, it's my hard-earned money...

I'll stay tuned.

 

Id say with a pressure reading of 0 while the truck is running (especially off and on) you definitely have a fuel pump issue, Im sure your savvy enough to have checked for shorting power supply etc.....

Lane, I wouldnt even fart around with the stock one, especially for $90 but be sure your regulated, you dont want too much pressure (more than about 6 psi) at the carb or you'll have problems......

Heres one I have in my "wishlist" at Summits website because of advice from someone I trust on another forum, I believe it is even regulated at the right pressure...... If linky no worky go to summits website and search for crt-p4070

Fuel Pump at summit racing

As far as the carb goes, personally Id buy a performer NON-EGR manifold and that 600 CFM edelbrock carb would be a perfect size for a stock 460 and go for it, get rid of all that mess,engine compartment will be cleaner, Truck will run better, have more power, and could quite possibly get better MPG, and eliminate MANY possible sources of vac leaks

My .02 my friend, keep us posted!!!!!!

EDIT:I see linky no worky, I figured as much, go to Summitracing.com and search for crt-p4070

 

do a search on this forum for "Hot fuel system" you will find alot of answers...Its 460 F250 thing........This fuel system runs through your oil pressure sensor and it has two relays one with power that turns on with truck running and then with just the key. I had all kinds of problems with mine and fixed it with info from here.

 

I say "Roger that," because there is a lot of places to check where things can go wrong before springing for a ninety dollar pump.

Also check on the intake side of the pump fule lines for possible air leaks. It can't pump air pressure.

 

pull the plug off of the oil pressure switch(if you look back at the firewall, you'll see the oil pressure sending unit, which has one wire, and the switch which has 2) and put a jumper in it, and see what happens.
And, BTW, what you're seeing on the framerail is the tank selector switch. The pumps are in the tanks.

 

Wow! I need to get a book on this truck. There's a pump in each tank?! I thought only my fuel injected '96 Suburban did stuff like that -- not a carbureted '86 Ford. I'll crawl under there again. I didn't realize that blocky item in front of the forward tank could be a pair of solenoid valves.

I guess a close-on-rise oil pressure switch isn't too much of a surprise. Without seeing a diagram in a book, I'd guess the "start" position on the ignition switch bypasses the oil pressure switch. It makes sense that one would not want the pump to run indefinitely if the engine wasn't turning.

I'll go look for that other thread mentioned above.

Thanks.

 

I did order a Haynes #36058 Manual (thanks, eBay) for the truck. That (and some free time to work on it) should be a big help.

The indicated pressure didn't seem to change when I switched tanks. I'll have to experiment some more. But that suggests the problem is not the pump(s). Perhaps I'll rig a bypass circuit that will let me just turn the pump(s) ON when I need to. Maybe I can narrow it down to something like the close-on-rise oil pressure switch or a relay.

I did find some additional info, searching for "hot fuel system" on the forums.

I miss the truck already, and I haven't even had it that long. The wife's Suburban is just not the same. Planning to move a refrigerator Sunday, and I'll probably use the 'burban and one of my trailers.

 

Still waiting for the manual, but I played with it for a moment tonight. Switching between tanks makes the pressure drop and come back. In fact, leaving the switch right between will result in no pressure. That might be a really cute anti-theft feature. A thief would fire up the rig, pull out into the street, then be immobilized when the gas in the carburetor bowl ran out. A guy stalled in the street with a stolen truck isn't going to wait around for the cops to help him. You might end up paying a tow and impound, but you sure wouldn't get your truck stolen.

I watched and watched, trying to see if flipping between tanks made the pressure come up to a slightly different value on each tank. Maybe, but if there's a difference it's pretty small. I didn't find intermittent pressure with the switch in either position. I wanted to rule out a bad switch that was coming and going.

I can't go very far with that temporary gauge on the hood, and the hood on half latch, but I might run it the half mile over to the plant when I go to work tomorrow. I'd like to see if I can make it act up again, so I can find out where we're open circuit. If there's a pump in each tank, then if I have an actual pump problem it should be confined to one tank. However, if it's an intermittent close-on-rise oil pressure switch, bad ignition switch, bad relay, etc., it wouldn't matter which tank I have selected.

I can't wait for that manual. This is interesting, but I have work for that truck to do.

 

I drove the wife's car to the plant this morning -- so I could aim her headlights during break. That was an exercise in futility; they have such a lousy beam pattern. I guess that's what I get for buying her a 2003 Shove-it-or-leave-it Malibu.

Took the Malibu home at lunch, then drove the '86 F250 back to the plant. It fired up and ran normally. But going home was a different story -- one told by the fuel pressure gauge on the hood, as well as the truck's behavior. Fuel pressure came up with the truck was cranking, then dropped as soon as I released the key to "run." Rattling the ignition switch or the tank selector switch had no effect. I think next will be to rig a simple bypass switch for the close-on-rise oil pressure switch. If the truck still acts up, and I flip the switch and immediately get fuel pressure, I'll replace the oil pressure switch.

BTW, you can get an F250 up to a respectable velocity on the fuel in the carburetor bowl. The controls get a bit stiff after the engine starves, though. Just don't turn the key too far off; that will REALLY make steering hard! I cranked it, fired up up, launched it, coasted, etc. I'm busy tomorrow, but as soon as I get time, I hope it will keep acting up while I set up the bypass switch.

This is educational...

 

If you look at your starter solenoid, you'll see that it has both small posts in use. One of the wires goes into a harness that runs across the radiator support and to the firewall on the drivers side. This is the hot in crank wire that powers the pump while the engine is cranking. Hook it to a 12V source, and you've got a running fuel pump.
I'd tell you the wire colour, but, that system has long been taken off of my truck, it all got replaced with a HD toggle when I swapped the cab.

 

Hey, thanks! That should be a quick and simple "get by," and is less work the making a switched bypass for the oil pressure switch.

By the way, if there's a pump in each tank, do they both run all the time, or just the one on the tank that is selected?

 

Just the one in the tank selected is powered.

 

That's kind of what I suspected; it makes sense. I'm actually a bit surprised the pressure is so close to the same, regardless of which tank is selected. Remember, I have the return blocked on that relief device from the "hot fuel system" that I showed near the top of this thread. Those pumps must be very consistent. BTW, I notice that 5-1/2 or 5-3/4 psi will drop to about four when you step on the gas and accelerate.

 

Well, I finally found a moment to pull the wire that 82F100SWB mentioned, from the terminal on the starter solenoid, and put a 14 gauge jumper directly from it to the battery. I heard a pump start. My gauge showed more pressure than I'd seen before, leading me to suspect voltage drop in the wiring.

I started the truck, then swapped between tanks just to see what happened. First two or three times, it was as before: pressure drops if the switch is centered, but picks up on either tank. This time, I could see a slight difference between the two tank pumps. Then suddenly, NOTHING when I'm on the front tank. Had to keep the switch on the rear tank to have pressure. Wiggled and fiddled, thought I saw pressure twitch up a fraction of a pound a time or two, but can't get it to pump on the front tank now.

I have earlier noticed an intermittent gauge. I took the rig the half mile to work today. Noticed the gas gauge said empty. I'd expect it to be near full. I don't think it got siphoned, since I have locking caps.

Now I'm thinking I may have problems with the close-on-rise oil pressure switch AND the tank selector switch. Maybe I can get chance to run the truck inside, crawl under the dash and search for loose wires.

This is becoming annoying. I'm about ready to rig a manual double throw switch and heavy duty wiring straight from the battery through the switch to the pumps. I want this rig to RUN.

 

In the "start" mode there is full voltage on the pump circuit. In "run" there is a built-in 0.75 Ohm resistance wire in the harness to reduce the voltage at the pump. There is a small fuel filter in the carburetor inlet that can cause problems but if you have erratic fuel pressure/delivery problems and the fuel pump is running OK then I'd suspect an "in-tank" fuel filter problem. 5 PSI at the carburetor inlet in "run" should be plenty.