I have a 1986 F250 with ano EFI 302. Over the past week, it has been hard to start randomly, would crank over but not start. Every time it was hard to start, the high pressure fuel pump would turn on when I turned the key onto the on position but would not turn off after a few seconds like it usually does.

Every time up until today, I could cycle the key off and back on and the pump would go back to acting right (running for a few seconds then turning off). And the truck would start.

This morning, the pump continuously runs and doesn't shut off. Cycling the key isn't fixing it anymore. Truck is turning over but will not fire.

Could this be caused by the low-pressure in-tank pump going bad?

Additional information, up until last night, my gas tank was open to the elements due to a bad seal around the vent-valve. I replaced the seal last night after it rained all day yesterday and ran the truck to move it out of the shop. Don't know if maybe I have water in the gas because of the tank being open like that.

 

I would check the fuel pump relay for the problem of it not cutting off. The fuel pump running all the time should not keep it from running though, you indeed may have some water in the fuel. I wonder if it will try to start with a shot of ether in the air snorkel.

 

I was thinking that the high pressure pump might be constantly running because it can't get primed.

But I'm gonna run tests when I get back to it

 

When the engine is running, it normally runs all the time. And the time period it runs during the first key on cycle is just that, a time period. It has no pressure sensors or anything on it to tell that it has fuel or not. I am thinking your fuel pump relay is sticking.

 

Got back to the truck later the same day. I hit the key and started the truck before the fuel pump had a chance to run too long. Truck fired right up.

The pump is shutting off after the allotted time for now. I think the relay is going bad.

If the relay works as it should, the truck fires up fine. If I start it before the pump has a chance to run too long, the truck starts fine. If the pump is allowed to run too long, the truck won't start.

My best guess is that the old injectors are allowing fuel to leak and flood the motor. No shops around here test or clean injectors, so my only option is to buy new when I can afford them.

 

Injectors can get dirty and dribble/drip fuel into the intake.

 

That's what I'm assuming is happening, but I've called just about every Shop in a four county area and none of them have the machine to clean injectors. So I'm stuck with running cleaner through my gas tank or buying new ones.

 

This might be a good read for ya ... Manual Injector Cleaning - The How To Thread.

Read the whole thread, especially post #5.

-Enjoy
fh : )_~

 

He has a bad ECU Computer.
The Fuel Pump Relay is OK.

The injectors are more than likely OK also.
If the clock in the ECU does not start the fuel pump(s) will run all the time the key is on and the engine is not running. Also without the clock running if you crank it the injectors will not fire and the engine will not start.

 

Excuse my ignorance about EFI on these trucks (mine's carbed and i'm more familiar with GM EFI)....Is there a fuel pressure regulator prior to the injectors (assuming so) ? If so, could the FPR be allowing too much fuel to the injectors if faulty?

 

With the fuel pump(s) running with the key on for more than one second and the engine not starting while they are running is a very common problem. It will almost always turn out to be the computer near 100% of the time. If he opens it up he will more than likely find bad caps in the computer. These caps cost under $1.00 and after they are replaced the clock will run again.

The Fuel Pressure Regulator (FPR) is a spring loaded device with vacuum to help the spring during high vacuum operation, idle and low throttle operations. The spring has no help during low vacuum operation and will let the fuel pressure go up to around 40psi for a 5.0L engine during WOT.
The FPR is between the fuel rail and the return line to the fuel tank(s).

 

The truck died at work again. Wouldn't start, smelled fuel really bad. It was getting spark and air. I think it was flooded.

I replaced the relay. And it's doing fine for now. It has a brand new computer and fuel pressure regulator.

I'm gong to clean the injectors soon, and see how it does. If it acts up again, I'll look into the computer, but I'm not good at soldering so I'll have to figure something out if it's bad.

 

If it floods again hold the gas pedal to the floor and crank it. When the computer sees the throttle wide open, and it's turning less than a certain rpm(cranking) it turns the injectors off. The computer goes into a "clear flooded engine" mode.

 

Alright, truck has been doing fine with a new relay in... until this morning. Fuel pump stuck on when I tried to start it, I cycled the key and the pump turned off and truck started fine.

After moving the truck across the yard, I shut it off and finished loading up my equipment for work. Upon entering trying to start the truck again, the pump continuously runs and truck won't start. I tried the method mentioned to clear the flooding to no avail.

I've noticed this problem seems to happen worse when we've had wet weather (like the last three days). I keep the truck parked under a shed, so I don't think rain is the cause. But maybe the 100% humidity is causing an issue.

 

Read post #11 above again.