I know you must be getting tired of all my post but i really need to figure this out..ok i have a 1991 f-150 ext cab with duel tanks.when i bought the truck the back tank never worked but ran fine with the front tank.well the truck sat for about 6 months while i had a tranny replaced and now it wont start. it idles fine if i spray the throttle body with starting fluid and will run for as long as i want it to but as soon as i shut it off it wont restart like it isnt getting gas.i spray it and it fires right back up.i can hear the fuel pump running constant it doesnt shut off as long as the key is on.i checked and it is getting gas thru the filter and i used a pressuer tester(tire guage) at the valve on the fuel rail and it is showing 70psi there i have replaced the fuel pressure regulator also...is there something im missing??? any help will be greatly appreciated. thanx tim

 

The last time we went into this, I argued that you had two independent problems -- the constantly running fuel pump, and the failure to start. I now think that these problems may be related and share a common cause -- namely something catastrophically wrong with the PCM.


Go to fordfuelinjection.com and follow the procedure to run a KOEO test. One of the following three things will happen:
1) The test will run and indicate "pass" on the check engine light(code 1-1-1 repeated twice)
2) The test will run and produce one or more failure codes which may help your diagnosis
3) The test will not run -- the "check engine" light will stay either always on or always off -- which is an indication the PCM is not running -- either dead or not getting power.

I believe that if the PCM is dead, the fuel pump will come on with the key and just keep running -- as you are seeing. This is because the PCM turns the pump on at "reset" (aka key going to the "run" position), but has to successfully "boot up" in order to shut it off. If it "won't boot", the command to shut the pump off never comes. The vehicle will have spark (because the TFI can supply spark on its own) but won't get any fuel to the cylinders (because the PCM never fires the injectors). You can have lots of pressure in the rails, but no fuel will appear unless the injectors are commanded to open. (the PCM is dead and not sending such commands, according to this theory)

The PCM might be dead due to a failure of the PCM power relay, and/or one or more fuses or fusible links. Or it may be a failed PCM.

Run that KOEO test and tell us what the monitor engine light does.

 

If you have someone who wants to help you, you should listen.

Run some searches too. This problem has been discussed before.

 

ok i might be dumb but whats the pcm? also i have found that somebody has messed with the wires and spiced a red one to 1 of the the relays and the other one is now a 4 prong and not a 5 prong...when i pulled out the 5 prong relay the pump stayed running but when i pulled off the power wire to the 4 prong it shut off i guess i will have to find the proper plug and rewire that relay and also last night when it was actually quiet enuff to hear i could hear what seemed like a vacume leak by the feul pump pressure switch and i check the vacume line by it and it seemed fime but when i sucked on the line the fuel pump sounded in a higher pitch...like it was running harder so ill replace that again and go from there...thanx for any ideas and thanx for the help so far tim

 

PCM = powertrain control module
also known as
ECM = engine control module
EEC = electronic engine control
"The computer"
"The black box"

You get the idea. It is the microprocessor operated collection of hardware that is supposed to sense such things as throttle position, engine RPM, engine load, etc and appropriately control the fuel injectors to supply the right amount of fuel, control the idle RPM, control the amount of spark advance, and operate various emission control devices.

In diagnosing your "no start" problem, it would be helpful to know if the PCM is alive enough to give you codes, or if it appears to be "brain dead". A PCM that cannot even control the "check engine" light is not going to appropriately control the fuel injectors, no matter how much fuel pressure you have. It isn't hard to read and follow the directions at fordfuelinjection.com, and see if the appropriate pattern of flashes appears or not.

The other thing that would be helpful is to have some idea of whether any fuel is reaching the spark plugs when you attempt to start the engine without starting fluid. Are they wet or bone dry after a few start attempts?

If "Butch" has done extensive work on your wiring harness, it may prove extremely difficult to figure this out over the Internet.

 

replace the fuel injectors !!!