I recently purchased a non running 1985 F150 5.0 Inj / auto (78,000 miles) from a nearby farmer, the truck has sat for several years (~2014). The previous owner mentioned the front pump, inertia switch and the fuel pump relay had been replaced in an attempt to start the truck, he also warned me the rear tank hasn't worked in many years and not to try it. I did verify the parts he mentioned had been replaced but there have been a slew of other problems.

Battery- the one mounted in the truck as well as the other two sitting in the bed were all bad; replaced with new

Battery Cables- the insulation was melted a inch and a half back from the missing cable ends; replaced w/new aftermarket

ECM Relay - wasn't turning on to deliver 12v to the ECM ; replaced w/ new aftermarket

ECM- once the new relay supplied 12v to the ECM, the fuel pumps wouldn't cycle with the key; replaced w/ reman aftermarket

Fuel selector valve - didn't cycle nor allow fuel to pass through from either the front or rear tank. Replaced w/ new OEM

rear tank and pump- tank was full of vanish and sludge, the in- tank pump was rusted and fell apart on removal. Replaced w/ new aftermarket
Fuel lines were flushed and the fuel filter and fuel pressure regulator were replaced (due to fuel sludge plugg

 

Plugging the filter and regulator port.

the pumps now deliver fuel to the injectors but the engine will only start with starting fluid, but once started it will continue to run on gasoline from the tank.

Ignition module- replaced w/ new aftermarket
engine now starts and runs with gasoline from the tanks but idles fast and throttle doesn't seem correct.

upper intake gasket- found the gasket broken with pieces missing, had carbon replacing the missing pieces (been running with this problem for a while. Replaced w/ new aftermarket

TPS at idle position read 1.32v on green wire instead of <1v
Replaced w/ new aftermarket.

 

The truck still doesn't start right.

What controls the fuel pumps to cycle on when the ignition is turned on?

The engine starts fine as long as the pumps cycle but if the pumps run but don't turn off after the three seconds, the engine won't start. When this happens the injectors click, the ingnition has spark.

any ideas?

Tad Petrie
Marion, TX

 

You have a fuel pump relay also. They are known to stick on. Have you changed it out? Also I would always pull the codes on these trucks. There is a 50-50 chance it may help you out. For instance if you get any ignition related codes, that could point to your fuel pump problem. The computer will not turn the pumps on if it doesn't get signals from the distributor. It will set a code if it doesn't get these signals or they are intermittent.

 

I don't believe I am explaining the problem well enough.

When starting the truck if the fuel pumps turn on momentarily when the ignition is turned on; the truck will start and run well.

If the fuel pumps turn on and stay on when the ignition is turned on; the truck will not start.

Over the course of the afternoon I would go out and cycle the ignition switch, eventually it did momentarily run the pumps again and the engine started. It has been starting fine all evening

Does the ECM control the initial fuel pump cycle?

Tad Petrie
Marion, TX

 

Near as I remember, yes, this is all controlled by the computer.

I agree with Franklin, pull the codes and see what the computer thinks is going on, this should help you (sometimes immensely).

 

ECM controls the 5-10 second prime. Then ECM causes pump relay to close to keep pump running. You can ground the EEC Test connector to make fuel pump run (if everything else is okay).

Do you have a fuel pressure gauge (are you seeing around 39-40 psi on the fuel rail)? If runs off "spray" but not fuel system - could be that injectors are plugged up from sitting with fuel in them for 10 years.

See this wiring diagram for how the pump circuit works. Note the engine size at the top of diagram to be sure your looking at the correct one. Electric Fuel Pump Control - ???Gary's Garagemahal


Fuel pump test connector:

 

So when you leave the key in RUN, the fuel pumps just keep running? Beyond the prime period? If so, I would suspect a stuck-closed relay.

 

You would think the engine would run if the fuel pump is running (even if relay is stuck closed).

Can you tell if both fuel pumps are running (the in-tank and on-frame pump)? I'm wondering if the low pressure "in-tank" is running but not the "high pressure" on-frame pump.

 

Thank you all for the input.

I came home from work and turned the ignition to the on position, the pumps (both) came on but didn't cycle off. I couldn't get it to cycle correct but I was able to get the engine to run with a little starting fluid in the throttle body. The engine ran but did very poorly, black smoke was rolling out of the exhaust pipe and the throttle response was poor. I shut off the engine and went in for dinner.

When I came back out I turned the key into the on position and the pumps came on and turned off after about 3 seconds. The engine started right away, ran smooth, had good throttle response and the exhaust was clear.

I went to retrieve trouble codes but can't figure out how to do it.

The red connector is by the battery but I can't locate the STI plug.
Any advise on where it is on a 1985 F150?

Tad Petrie
Marion, TX

 

If I'm not mistaken, the STI is the single wire next to the red plug, it normally has a gray, plastic covering for that electrical connector.

Ya know, I had all this stuff up online here in the stickies/subforums at the top of this site; some of it is still usable but photobucket took away lots of pictures so I'm not sure how much stuff works there anymore.

But please please please go nose thru the FAQs and HOWTOs subforums, you might find some real golden nuggets there.

 

Thank you; I'll go look

 

This link tells you how to do it.
EEC IV Self Test hookup

I think Chris is right, the wire you are looking for is right there in the picture beside the red plug.

 

I had thought the same and did install a jumper between the loose connector and the diagnostic plug, I could here relays or solenoid click and buzz but the emissions light didn't come on (does cycle on when the ingnition is first put in the run position)or flash so I thought it was an incorrect wire.
I'll try using the test light or analog meter when i get home.

 

These first generation fuel injected setups can be a little different. You may not be able to use the check engine light to get the codes on these. You also may find you do not have a fuel pressure test port on the fuel rail.