no spark

[morefried]

I got a 91 4.0 4X4 and it will run some times for an hour some times 10 minutes then it will stall and not have no spark. And its real geting to be a pain . Ihave a total of about 1000 miles on it sence i put new valves in the heads. I have changed every part of the ignition coil pack, crank sencer ignition module and the computer and it still does the same thing. I have know ideas left any help would be great thanks

 

[BradE.]

When were the plug wires changed last? Plugs also.

 

[morefried]

spark plug wires are not the problem i just checked

 

[MrShorty]

Just a couple of ideas.
When it won't start is the PCM getting power?
How about grounds? engine ground PCM ground?
Does the fuel pump have power when it won't start? Is there fuel pressure?

 

[Runnin'OnEmpty]

The fact that it's a 91 makes me mention the ignition switch. Ford had a lot of trouble out of them in the late 80's and early 90's. When it dies on you, does anything else go out; such as the radio, A/C, instrument lights, etc.? If so, the switch is bad.

 

[morefried]

every thing stays on. you can here the fuel pump run