I have a Explorer, 94 that only sarts about 30% of the time. I get spark at the plug. The fuel pump runs and shuts off w/ relay click in about 2 to 3 seconds and then it will start. The rest of the time I hear the pump but no click from the relay. I have had to have it towed more than once and this all started about 3 weeks ago.
I have had it at a service garrage where he checked the wires to the pump, replaced the fuel filter, checked the cut-off switch, we replaced the relay, checked the wires into the transmission. Before he was done trouble shooting the unit would start. GREAT?
The next time it was towed to the Ford garrage. Of course, it started for them there and could not find anything. Told them what it was doing and they looked at the wiring diagram and said that they were not sure at all. One person there suggested that the PCM may be bad but it is expensive to replace if that is not the problem.
I have found that by just trying the ignition switch I can, once in a while, get the relay to click and then it will start right away. Most of the time I just hear the whine of the fuel pump and when I hear the whine it will not start for anything.
ANY SUGGESTION? I REALLY NEED THE ASSISTANCE. SOMEONE MUST OF HAD THIS PROBLEM BEFORE. All positive comments are appreciated since I am looking for straws.

 

I looked thru my manuals & cant find anything that tells me EXACTLY how the PCM/ECA controls the fuel pump relay. But I did find that "For safety reasons the PCM/ECA removes power from the fuel pump when ignition signals are not present." I dont see any way that your PCM/ECA could be receiving a bogus "ignition signal" & keep the pump running when it shouldnt be. So my guess would be that you have a bad PCM/ECA.

It would be interesting to know WHY a constantly running fuel pump would prevent starting. Maybe one of the other guys will know.

 

One thing that we have been discussing at work is that it may be possible that the pump shuts off, after building preasure, until the initial fire or start....just in case so it doesn't continue to feed gas. In other words a signal that the engine is running throws the relay again. Sort of a On (get ready) Off (set & ready) Go ( engine is starting so give more fuel. Just an idea...but I am willing for suggestions. Someone else has had to have this situation.

 

According to the wiring diagrams for my 87 Ranger & 95 Taurus, there is no way for the PCM to know what the fuel pressure is. I think the 2 second run time is simply controlled by a timer in the PCM
Turn the key to run & the timer grounds the fuel pump relay for 2 seconds.
Turn the key to start & the PCM senses ignition pulses & once again grounds the fuel pump relay & off you go.

 

That's how it's supposed to work. In your case, it sounds like something is causing the fuel pumps to stay on, and whatever electrical fault is doing that is also disrupting the computer's signal to the injectors, the computer itself, or the ignition module.
When it won't start, what is the fuel pressure at the rail (measured with a fuel pressure gauge at the schrader valve)?
Do you hear the fuel injectors opening?
Will it start if you squirt a little starting fluid into the intake?

 

The best answer I can give, at this time is that the fuel pressure measured by a mechanic, I am not, was about 44. I am not sure about your question of hearing the injectors. There is spark but I don't believe that the injectors are opening until after the relay sets for the fuel pump. Then it will start. If the relay does not set, it will not start. Myself, and the mechanic both agree that the clicking is from the set of the relay for the fuel pump. One thing I noticed today is that if I try to start it or turn the engine over a little, that after a few trys the relay will set, and yes then it starts. It was about 8 or 10 trys this afternoon and about 4 trys this evening. With the weather the way it has been here in Ohio lately, I cannot say with any certanty if the cold is having anything to do with this problem or not..