1992 Ford F-250 Won't start

JUSTIN2013

MEMBER
1992 FORD F-250
5.8L
V8
RWD
MANUAL
237,000 MILES

I turn the key to on position to where the fuel pumps cut on and they run for like 30 minutes to an hour and then they'll shut off and my truck will crank fine. It won't crank if fuel pumps are still running, but sometimes it will and the check engine light will be on which makes it run kind of funny but the check engine light will go off and it runs perfect! But now fuel pumps keep killing my battery and it's just getting very anoyying now and I've replaced a lot of stuff to try to fix it. Ford place told me it was the check valves in the fuel pumps and told me I needed to get new ones so I did, didn't work. Next I replaced the fuel pressure regulater and checked all fuses and relays and still didn't work. Then I was told it could be the fuel injectors, so I replaced them and the fuel filter, still same problem. I checked around online and some people were having sort of the same problem and they said it was the PCM OR ECM. I took the computer out and checked it and replaced all three capacitors because one of them was like blown I guess so I just went ahead and replaced all of them in there. Now I'm out of ideas. Can you help me please?

1 Reply

CARADIODOC

MECHANIC
33,737 POSTS

Someone is just guessing and you're replacing parts without diagnosing anything. As you can see, that gets real expensive, and it's not an effective way to troubleshoot a problem.

The fuel pump should only run for about one second after you turn on the ignition switch to insure fuel pressure is up for starting in case it bled down overnight. It should never run any longer on any brand of vehicle unless the engine is rotating, (cranking or running), because to continue running would pose a major fire hazard. If a fuel line gets ruptured in a crash, raw fuel would get dumped onto the ground. Instead, the engine can't run without fuel pressure so it stalls. That kills some sensor signals which tells the Engine Computer to turn the fuel pump off.

There's three things that will cause a fuel pump to run continuously. The first is a defective Engine Computer. I know the capacitors you're referring to because I find them in tvs, but you aren't going to solve a problem in an Engine Computer with those.

The second thing is a sticking fuel pump relay. You can unplug that to stop the fuel pump, but when you do, try to feel for the light click of it turning off. If you can detect that, more than likely the computer is keeping it turned on.

The third thing, which could also be related to the no-start condition, is a dirty signal coming from the distributor pickup coil. Unplug the distributor. If the fuel pump stops running, it's because the pickup coil or the TFI module is generating noise, in effect, static, and the computer is interpreting that as the signal is sees when the engine is rotating. Any signal, even when it's incorrect, can trick the computer into turning on the fuel pump relay.

I'd have to dig up a wiring diagram to see if your engine uses a crankshaft position sensor in addition to the distributor pickup. If it does, unplug that too. Three-wire sensors have electronic circuitry inside that can generate that noise. Two-wire sensors have only a magnet with wire wrapped around it. There have been cases where that magnet has cracked and poor signals get generated. Usually that won't make the computer turn the fuel pump on though, and it often causes popping and backfiring due to it generating multiple signals.