I have a 1986 f150 with a 5.0 fi with an AOD trans I have had it around 2-3 years and do not know its history. All I can say about it is I drove it home which was about 10 miles and it ran like crap it wouldnt rev very high and was very hard to keep running and surged real bad. I messed with it a little when I got it home looking for vacuum leaks and making sure all plugs were firing but then it got to where it would just start sputter a little and die I don't have a lot of time at home with what I do for work so it has just set in my drive for about the last 2-3 years until the other day when I decided I was going to check it out again. So here is where I'm at on it lets see if someone has any ideas it still does the same thing as it did the last time I messed with it but I have changed the plugs wires cap and rotor cut the cats off thinking maybe they were clogged put on new fuel filter and ran the codes which came up with only one checking them with key on engine off which was for the map sensor which I tried unplugging it to see if it made any difference which it didn't and I have figured out the alternator is out and I believe it has a dead short in it causing the battery to discharge pretty quickly and it has about 40 psi fuel pressure but I have no idea what it has running since it won't run long enough to check and the tps checks out good also. Well that's where im at lets see if anyone has any ideas. Thanks Tracy

 

If its carbed pour some gas in it and see how it behaves. If it runs the gas out normally its a fuel related issue.

 

It's a 5.0 fuel injected I shouldn't have abbreviated in my original post

 

What is the diagnostic code number being given by the computer? KOEO test only, correct? No CM codes?

I'm guessing you can't keep it running long enough to do a KOER test?

 

I can't remember the code but it had something to do with the map sensor I have a new one but haven't been home yet to try it out I drive a truck and don't get home but about every 3 weeks and yes you are correct I can't keep it running long enough to check the codes KOER. I have been reading about the fuel resorvor (can't remember the correct name for it) that switches the fuel tanks with the pressure from the in tank pumps and that is sounding more and more like something I need to check out when I do get home. Keep the ideas coming and thanks for the reply.

 

I have the 1986 FoMoco Engine/Emissions Diagnosis Shop Manual but can't look anything up without a code.

As for fuel, check your fuel pressure and output rate up at the engine.

 

And I will run the codes again when I get home it's been a long time since I did it and don't remember exactly what they were but I know one was for the map but I have slept since then and can't remember the others but I don't think there were any major ones that would keep it from at least running. Oh one code was for the TPS but it just needed to be adjusted and I checked it with a volt meter when I adjusted it and it checked out good But had no effect on the truck

 

The fuel pressure is 40 and it holds it pretty well but I haven't checked flow rate yet. I don't get as much time to mess with it as I want with my wife and her honey do list

 

If the fuel pressure holds and the volume is fine then the problem isn't with the tank selector valve. Yes, those things can do "funny" things, like pull from one tank and return to the other, but if you have good pressure and flow your engine problems are elsewhere.

On the other hand, if the pressure drops when you try to start the engine and/or the flow is very low then it may be that valve. Or, the frame-mounted pump. Or the in-tank pump.

 

I KNOW THE ANSWER TO THIS ONE!!! My 86 JUST did the same thing. It was the magnetic pick-up trigger and control module.

1. Check for spark. Take and old plug and plug it into the coil wire and ground the plug to the engine or battery if you have some wire laying around. Have someone crank the motor for you. No spark? Time to check the input into the coil.

2. Coil check. Pull off the plug going to the coil. Get your voltmeter and test each wire with the ignition on. One should read a constant 12v. The other will be lower. Keep your voltmeter hooked up to the one with lower voltage. Have someone turn the motor over. The voltage should now fluctuate up and down. If both wire check out fine then its the coil. If you get a very low voltage on the one wire and no fluctuation then its time to have the TFI module checked down at autozone.

3. TFI module check. Take it off the distributor and have autozone check it. Mine was bad. But that didn't fix my problem. The magnetic pick-up trigger was bad also.

4. Magnetic pick-up trigger. You cannot test it. Its about $20, just replace it with the module. To replace it, remove the distributor from the engine. Knock out the spring pins in the cam gear and guide bushing. Gently tap the shaft to remove the timing gear and bushing. Slide shaft out of distributor. Replace pick-up trigger. Reassemble dist. place engine on TDC and align #1 plug slot in cap with rotor. Continue replacing wires in the correct order.

Im betting it will fire right up.

 

Oh, don't forget to pull your SPOUT plug and set initial timing to 10degrees BTDC.

 

I had problems with my fuel system as well. I don't remember the symptoms other than it simply wouldn't start. The selector valve had fuel running from the front tank to the rear tank and fuel kept simply gushing out the rear tank. I removed the selector valve and rear tank. All I run is the front tank now.

 

Yep, Ray's was the poster child on what the valve could do wrong. That's when I learned how easy it is the bypass the thing.

 

Thanks guys I'm going to try and get some work done to it when I get home

 

Keep us posted. 918-508-9816. Call me if you need help troubleshooting the ignition. Its still fresh in my mind.