im ready to torch my 95 f150 5.8L. ok before it left me stranded i noticed it was idling rediculously high one day and later that night went to go home and would not start. towed it home beeen workin on it since. i changed the idle air control valve but the truck will not start unless i use either or starting fluid. once it starts though it will stay runnin but still idles high unless i blank off the iacv. so i gather there is something tellin the computer that there is alot of fuel to open the iacv when in fact there isnt enough fuel to start the truck. ive checked the fuel pressure to the rails and im getting no codes. what can be the problem?

 

A good place to start would be to check for a good sized vacuum leak, hose off,split etc.

 

In addition to what Hanky said, just to be sure everything is OK you should double check the fuse that controls the injectors.

 

yeah ive cheched all that plus if there was a leak the iacv wouldnt be opening up all the way. i believe something is telling the computer there is alot of fuel and i need more air hence the iacv opening all the way. im just not sure what. i might have to try some O2 sensors but i really dont wanna just throw parts at it.

 

ok no vac leaks no blown fuses i need a schematic on the wiring of the sensors injectors and electronic engine control systems.

 

Usually when the computer gets the info from the o2 sensor that there is a rich condition , the computer reduces the injector on time ,shortens the injector pulse width, but doesn't alter the air control. You might look for an RPM signal fault . That might cause the computer to increase the air opening thinking the engine isn't idling fast enough.
There is the possibility of a charging system problem where insufficient voltage is supplied to the system in order for the computer to operate properly and yet when once started the output is enough to allow it to keep running.
A thorough check of all the main connections is a good place to start checking.
Were you able to try some carb/ choke cleaner to check for a vacuum leak?

 

i have vacum gauge pressure is normal and steady. also have fuel gauge and pressure is correct. almost certain its electrical something not telling the injectors to supply fuel at start up. even with the iac unplugged and closed or blanked off, i still have to use either/ carb clean to get the truck to start. but once it starts it stays running. time to check wires. very frustrating you know for an ex aviation electronics expert i still hate this stuff. makes me remember why i got out the navy. also where can i get a list of theses sensors and values? i never have these problems outta my 86 z28 but then again i gutted the electronics and swapped out the 305 for a 406 and msd ignition system.

 

Come now,,, It's time to put all that good stuff you learned to work.
When the engine cranks to start, the fuel is supposed to be there already. When you first turn the key to the on position you should hear the fuel pump run for about 2 seconds then stop if you don't go to crank the engine. Do you hear the pump when you turn the key on? I will try to explain some of this as best I can.
There is a check valve in the fuel pump assy that is supposed to prevent the fuel from draining back once the engine is shut down. If that check valve isn't doing it's job you wind up with extended cranking time to get it to start. Don't know if this is your vehicle's problem yet. The computer will continue to keep the fuel pump relay energized as long as it receives an RPM signal from the dist. assy while the engine is running. If the RPM signal is lost for any reason the fuel pump relay drops out and fuel is cut off. I know this is simple stuff for you so maybe it will shed some light on why you are not getting fuel to start.
There appears to be some relationship with that RPM signal and the IAC valve with the increased air at idle, that's what got my curiosity going.

 

As you know ,if the voltage is not sufficient to either energize a relay or hold it closed that is also a possibility. Yet once started, the little extra output from the alt could just be enough to hold the fuel pump relay energized if that is the problem. Also , remember what poor connections can cause. So I would suggest that you check all the connections at the dist and to the module attached to it. I will check my info to see what else could give the problem the vehicle has.

 

great feed back but i also during all this just found that the egr was bad deff. bad and had to replace. and now have noticed the front cat. glowing cherry red.
this truck is fallin apart. what did i expect for pickin it up for $3,000 a year and a half ago with 130k miles. it was clean and under the hood was too. i got it from an older guy who took care of it and had all the maintenance tickets.