My 92 f150 with a 4.9 had been running rough and dying over the last week. I thought I had the problem fixed when it died and I found a loose battery cable. Replaced the cable ends and the truck started fine but when I shut it off it would not restart. I cant get it to start for anything now and I need it to get to work.

I noticed that the fuel pump continued to run anytime the key was on. Im pretty sure it would always run for a couple seconds before and then shut off, but now it just keeps running until I shut the key off.

I replaced the fuel pressure regulator today, but that did not help. Also, now when I try to get computer codes it will not let me. I dont know if that is due to the pumop running or not.

Please help.

 

Anytime the fuel pump stays running with the key on it's either a stuck fuel pump relay or most likely a bad engine computer (PCM). Combined with the other issues you stated, it's most likely the PCM. Remove the connector, the retainer screws, then pull it out and open it. Look for signs of moisture, burn marks or leaking capacitors.

The PCM is located under the brake master cylinder/vacuum booster. It is removed from the engine side of the firewall.

 

I pulled the PCM out and opened it and dont see anything that appears burnt, or wet or "Abnormal" (not that I really know what normal is in this thing). I also swaped out the fuel pmp relay with another and it does the same thing. I do notice that the relay is clicking wildly as if it is getting power and then not getting it.

I dont really want to replace the PCM unless I am pretty sure that it is the problem. Is there any way to test this?

 

Just curious, if the fuel pump is running all of the time, shouldnt it still start since there would be pressure?

 

It will not start because the computer is not grounding the fuel injectors.
If the fuel pump does not run with the computer unplugged and the key on then you have a bad computer.

The fuel pressure regulator (FPR) or the fuel pressure has nothing to do with the fuel pumps running or not running.

 

Ok. So I turned the key on with the computer out and the pump did not run. So it is safe to say the computer is bad.

 

I had the EXACT same problem a few months back on my 91 4.9 turn on key fuel pump stays running and clicking relay and no start.... Replaced the PCM did the trick a few bucks but that was it!!! Thanks to FTE for solving my problem and im sure it will solve yours!! Good luck!
Donnie

 

Anyone know if the computer has to be an exact matc or will any of them from a truck with the 4.9 and standard Tranny work. There are a bunch of different options.

 

It will at least run with any 92 4.9 M/T module. The rest has to do with CA vs. Federal emissions, minor changes to sensors throughout production runs, etc. I used to sell computers and with Ford, Nissan, and Benz it's very rare that the numbers on the nameplate will match exactly even though it's the same computer. A computer for a 92 commercial truck shouldn't run you much $$, that's the good news.

 

Thanks for your help. I finally got the new computer today and the guy said to make sure to check all relays and switches before installing it or it will void the warranty. How do I go about doing that?

 

I guess what I am saying is can the components that need to be tested be tested at the computer plug?

 

Well you'd really have to check every circuit to the computer to say 100% there is not a problem that would kill the computer.

A computer just isn't that expensive so rather then go through all that I'd just take my chances.

You did enough testing as far as I'd be concern, the PCM and fuel pump circuits tested good without it connected so I plug it in and go for the "run". Just make sure the battery is disconnected when doing so, apply very light coat of dielectric grease to harness side connector before plugging it in.

 

I know I am bringing up an old thread but I have to ask because I just replace the PCM two years ago and I'd like to have to do it again. Here's my symptom. Hope it's not the PCM.

Turn the key to the on position and I hear what sounds like to fuel pump, but higher pitch than normal and just keeps running. Try to start and it cranks and cranks but no start. If I leave the key on for a few to 5 minutes, eventually the fuel pump changes pitch and pump shuts off. Try to start and she fires up and runs pretty well. I don't drive far but I've only one instance when it did an intermittent run then die thing, but I made it home.

Also, when its in the "no start" mode, if I spray some carb cleaner down the throat of the intake, she sparks and starts up and keeps going.

I guess I should note that the truck isn't used much these days as my father in law is doing chemo (i gave hime the truck to use around the ranch some years back) so it probably only runs once every 6 weeks or so, or when I'm visiting him (and I live 16 hours away so that's only 5-6 times a year), and it sits out in the Oregon rain the rest of time. It's only go about 70000 miles on it and we'd really like to keep her going, but also hope it's not another PCM. Thanks for your help.

 

I had the same problem with my 94 ford F-150. It would run sometimes and sometimes it wouldnt. I would be driving it and it would start running real rough and then try to die. One day when i went out to start it, it wouldnt start but just crank all the time. I replaced the alternator and it quit having the problem. Im not saying that this might be yours but have the alternator check out. Just trying to help out. Let me know what you find out.

 

I would say for what ever reasion the clock is not running in the computer.
This could be a bad computer, poor ground to the computer or voltage.

I cannot answer why it start on starting fluid and then run OK unless the clock started running the same as if you left the key on for that time span. I would guess bad caps in the computer.
As you know with the pump running and not timing out the fuel injector will not fire either without the clock running.