1986 F250 SuperCab 4x4, next to last year of carbureted 460, T-19 four speed, factory dual tanks.

I bought the truck in 2005, and it does more sitting than driving.

I chased some fuel problems, also replaced carburetor. A friend who worked on it and tried to reconcile what he found with the manual, said it must be a late 1986 because it appears to have a 1987 fuel system.

It will sometimes just seem to shut down, then will fire up and run again.

It took me quite a while to figure out it was fuel. I'm used to sputtering and coughing with carbureted rigs; I equated immediate loss of power with ignition or fuel injected vehicles. I actually have a spare ignition module on the left fender liner, ready to swap at a moment's notice. I even replaced the ignition switch - not the lock cylinder, the switch. I had an issue with turning it off and not really being off, the aftermarket Kenwood still receiving accessory power.

Finally, when I was recently trying to track fuel consumption and accomplish a mission on only the rear tank (did not quite succeed), I experienced about four momentary shutdown & revive events. I got suspicious and really started watching closely. I believe this only happens when running on the rear tank.

Can the in-tank pump stop momentarily then restart? Is it more likely that I have an intermittent connection somewhere in the dash switch/selector valve circuit that picks up the rear tank's pump?

 

No 1986 has a 1987 fuel system.

1985/86 F150/350: The fuel tank selector valves have been CRAP since day one! There are two types:

E5TZ-9189-A .. Fuel Tank Selector Valve - 3 ports / Available from Ford.

MSRP: $253.13 / silverstatefordparts.com online price: $174.66 / Gaudin Ford ~ Las Vegas NV
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E5TZ-9189-B .. Fuel Tank Selector Valve - 6 ports / Available from Ford.

MSRP: $398.70 / silverstatefordparts.com online price: $275.10.
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The 3 step scenario of a failing DuraSpark ignition module:

1) Module overheats, engine dies. Module cools down, engine restarts almost at once.

2) Module overheats, engine dies. Module cools down, engine restarts in an hour...or so.

3) Sooner or later, usually sooner, the module overheats, BURNS OUT! Now the engine will not restart.

Taking the module to an autoparts store to be tested: Will test OK unless the little charmer has burnt out.

If the module is located on the left fender inner apron (I cannot recall where it is on 1986's), when replacing it, use some washers to space it further away from the apron.

Engine heat, especially when radiating from a V8's red hot left exhaust manifold, is the mortal enemy of these modules. So, the more airflow around the little charmer .. the better.

Modules identified by a colored plastic square above where the wires feed out.

1981/89 F250/350 & Econoline 460 will have the blue module, t'was introduced in 1976, used into the 1990's on myriad FoMoCo vehicles.

1U2Z-12A199-AA (replaced D6AZ-12A199-B & D9VZ-12A199-A) .. Ignition Module - Blue (Motorcraft DY-893) / Available from Ford.

MSRP: $74.20 / silverstatefordparts.com online price: $46.93.

 

Does this truck have the starter solinoid with the s on one side, and the I on the other?
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I remember a problem with one I had of that era, the wire coming from the I on the start solinoid had something to do with the signal to the fuel pump.

 

I appear to have a slightly different starter solenoid. I seem to recall buying a fuel selector valve from O'Reilly's but not using it - giving up because it had different connectors, but not before I caused myself a lot of grief. The truck has a fuel return line (older guy in parts house told me he worked on 460 Ford motorhomes at one point, and they disabled the pressure relief valve and return line to improve fuel pressure and help the motorhomes with fuel issues) and it has two tanks, so that would be the selector valve with 6 connections. Also, I installed a small switch to bypass the oil pressure switch that won't give you a fuel pump until you have oil pressure. The old carb leaked down, so I'd flip the switch and turn the key on until the seatbelt buzzer stopped, then pump once and start.

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^ This is B6AZ-11450-A .. Starter Solenoid, introduced in 1956, also used as a battery relay on 1973/96's with dual batteries.

1972: Ford introduced another starter solenoid (D2OZ-11450-A). It's a different shape than B6A and only has a one wire connector.

1986 F250/350 & Econoline 460: Two possible starter solenoids, with or without electric fuel pumps.

Both these solenoids are the same shape as D2OZ .. but have 2 wire connectors.

 

Grrr...double post.

 

So.... Occasional fuel shutoff that comes right back... Only happens on rear tank... Is the most likely culprit an iffy contact in the selector valve?

BTW, my (2) ignition modules are on the plastic left inner fender liner, but about as far from the engine as they can be without running into engine compartment metal.

 

The I terminal on both styles is hot with the key on, and send a signal to the fuel pump. If I remember correctly, this year truck they called it a "hot fuel system"
On my truck, someone had replaced the solenoid with an aftermarket solenoid, and for what ever reason, it wouldn't allow the pump to work right.
I replaced it with a Solenoid from Ford, and had no more trouble.

It has been 15 years since I sold this truck, so I hope I am remembering things correctly

 

Remember, it only seems to happen when I'm on the rear tank. Doesn't that argue for the starter solenoid connection being fine, but anything in the pump selection scheme being questionable?

 

Missed that part.
Now I'm thinking a bad ground somewhere.
I had an 89 f 350 that I had to add a ground into the tank circuit way back when.

I tested at the pump on top of the tank, and found the ground to be intermittent, so I added another ground from the frame to the ground wire going to the pump

That helped for a while, That truck eventually succumbed to salt, and winter. ( I live in the middle east coast, where they paint the roads with salt in the winter)

 

Now that's worth checking. I just recently installed a running ground from battery to my trailer connector. One rusty screw to the frame doesn't cut it.

 

I would do the ground on the fuel tank and would eye that module on the fender liner. Vibration will kill it. Make sure it has the metal straps installed on the other side of the liner. I would also put a ground wire on the case bolt straight to the battery. I left Charlotte on the way home in 100 degree temperatures and me and that module (85 F-150 4X4) drank a coldpack of Miller Lite with it getting more (damn thirsty box). About every 50 miles it had to have a beer.

 

That's an unhappy mental image, pouring cold beer over that aluminum module while thirsting away in 100 degree weather.

 

Here is a good visual. As I was pouring beer on it outside of Bluefield, a cop unnoticed walks up beside and asks what's wrong. I did not realize it was a cop as I was trying to get all of the beer on the box and my back was towards him. I said that the bi--h had a hangover and I am fixing her. Well, I ended up doing the DUI checks after he said he smelled beer on me. Hell, stand in a cloud of beer steam and you will smell like it. I passed his silly test except the heel/toe and told him that I could not balance on my left leg as the knee and back was shot. He let it pass and let me keep the beer so I could get home. LOL

 

At least he didn't catch you p'n on it......LMAO