Howdy yall. I have an 88' f-150 super cab (2 door with the tiny backseat), 302 5 speed manual and i can't get the fuel pumps to come on. first a little background:

i bought it about 5 years ago. when i got it, it didn't run. saw the previous owner had taken all of the wires off the solenoid for some reason. so after wiring it all back up, it still wouldn't start. we took a crap shoot in the dark and just decided to replace the computer from one in the junkyard (computer was from a f150 with automatic trans (diffent computer), but it cranked up, and ran. then a few weeks later it started to die when running. if i hit the gas it would die, but it would idle then die. after a few minutes of cranking it would start up, idle for about 3 to 4 minutes then die again when i checked fuel pressure there was none. if i tried to crank it a few times, and checked pressure again, a little gas would dribble out (low pressure). got tired of messin with it, and it sat for about 4 years, till i recently decided to tackle it again.

So now of course it still won't start. the fuel pumps aren't comming on. i replaced both relays and the computer with a reman one from advance auto (the correct one this time, lol). still nothing. if i pull the fuel pump relay out, and jump the two fat wires, the pumps come on, and when i check pressure at the fuel rail, gas shoots out. i tried to start it witht he jumper wire on to keep the fuel pumps on, and still nothing (injectors aren't firing). if i spray starting fluid in the throttle body, it will start up and run for a few seconds smoothly till the starting fluid runs out. if i keep spraying a bit of fluid while its runs, it'll keep running till i stop. the ECC relay is getting power from the ignition, and both fat wires are hot with ignition on, and only one hot with ignition off. with the ignition on the fuel pump relay is getting power fromt he little wires, and only the yellow (always hot power wire) is getting power, and the other fat wire going to the pumps isn't geting power.

so form what i can tell the computer isn't allowing the injectors to fire or the pumps to operate. any ideas? i'm at such a loss. thanks

-Mike

 

After reading thru the topics here, i looked at somethign else. soemone here said that the check engine light should come on when the key is turned on (not to crank it), and should go out in a few seconds as part of the pre inspection or something like that. so i went out and checked, and it comes on VERY dim, hardly noticable, then goes out, and then comes back on, or it will just stay on. or flicker off. it was kinda random. do you think i may have goten a bad computer?


the other thing i read was one guy saying if the voltage regulaor in the alternator goes bad, it can cause the truck not to start. i'm on my way now to test it, and see if thats the problem, and i'll let ya know.

 

You provided so much info that I'm confused , and it doesn't take much in my case.
In my state of confusion might I suggest that you check all the ground connections especially the ones on the engine and sheet metal. It does sound like one of them has a poor connection.

 

I agree with hanky in that checking grounds are a good start. Another place to look is the injectors themselves. I had a camaro come to me with a similar problem and after many hours of looking I found an injector that was randomly grounding, you can see if power is coming to the injectors with a noid light set, or a quick makeshift with a peanut bulb and bend the wires out.

 

sorry wanted to be as descriptive as possible, lol.

I'm going to borrow a noid set from my buddy, but right now i just can't get the pumps to come on. if i pull the fuel pump relay, and jump the 2 big wires, the pumps come on. i believe the issue is the computer just isn't functionng, for whatever reason (either its bad, or something else like a sensor or something not letting the computer operate).

does anyone know of something that would not let the computer fire the injectors, or make the pumps come on?

btw, i tested the alternator, and it tested out good, but the connectors on the alternator (mine has 2), slid easily on and off, so i don't think its making good contact. i picked up some new ones (very hard to clip on and off), and will splice them on 2morrow. and keep hunting for bad grounds.

i kno i'm getting long winded, but this is the last question i swear, lol. does anyone have some kind of diagram that shows the fat computer connection and what each pin goes to? that would sure make tesing wires a lot easier.

thanks

-Mike

 

If the computer does not get an RPM signal from the dist, it will not keep the pump relay energized nor fire the injectors. What is puzzling is that it will run with starting fluid.
Going back to your original post, You state that the small wires going to the fuel pump relay both have power. One of them is connected to ground. You should not be getting power from both terminals unless you lost the ground for the relay coil of the fuel pump relay. I would suggest that you remove the relay and determine which one is the hot side , then check for a good ground for the other terminal. That might explain why the relay won't close completely and feed the fuel pump with power.

 

oops, sorry. i ment to say that only one is getting power, and the other isn't making contact with ground. i believe the computer grounds the relay, correct? so that end of the relay shouldn't ground unless the computer allows it, correct? or am i misreading the electrical diagrams?

and yes, if i spray a bunch of starting fluid in the intake (spray for 6 to 8 seconds), it will start up and idle for about 10 seconds, then die (but no fuel pressure at all).

 

I believe hanky might be on to something here. One of the grounds you are looking for is the located LH Inner Fender behind Headlamps, still looking for the other. As for the relay, maybe these will help…

 

Awsome, thanks. I'll start checking wires tomorrow. and get back to yall. thanks again

 

Yes , you are correct , the ECM does supply the ground for the fuel pump relay from pin 22 thru the tan and light green wire . I would confirm a good ground is available at pins 60 and 40 since this ground comes from the neg batt term direct to the ECM.
If you have good spark when cranking , I would suspect the ECM itself.
Lately there have been quite a few cases of defective " rebuilt replacement" ECMs, PCMs.