I sure could use some help. My 91 f-350 has a 4.9 six. It will only
start when I use starting fluid and then runs very poorly. I've
tuned it up, replaced fuel filter twice, replaced map,and replaced tps. Please tell me what I need to do next.

andrew gleason

 

Have you pulled any codes out of the
computer??

Steve & the Rockette
'63 F100
'68 F100
'72 Capri 2L
'73 Capri 2.6L V6
'73 MG B GT 2.6L V6(Ford)
'98 Contour SVT 2.5L V6, That blowed up real good...
'01 ZX2 (No Mods yet)

 

i would start with a fuel pressure test.sounds like pump may be week

 

The computer will not give me any codes or anything. The check engine light will not blink at all with jumper wire installed and switch in the run position

still need help

andrew gleason

 

checked fuel pressure.. 45 psi is that enough pressure?


andrew gleason

 

I side with the advice that its a fuel delivery problem. The fuel system won't generate codes. I don't have my book, but 45 seems low for the high pressure pump, but not real low. The regulator brings it down to 25 or something like that, so that might not create a complete no-run condition.

Check your coil and ignition system too, a real weak spark would work with starting fluid but not gas. Pull a plug look for spark, if not cvheck rotor and cap. Then pull the coil wire and turn it over to see if it arcs to the block.

Then you'd know you have a good spark, move to ensure the high pressure pump is running, turn on the key, listen for it (should run 2-3 sec and then quit.) If that works, I'd open my gas cap to see if it sucks or blows air (maybe the tank vent is clogged and you have a vaccum lock, after that I'd turn my key on a couple of time to presurize the sytem and then, I'd remove the plenum and pull an injector to verify that fuel makes it into the cylinder and under pressure.

Since it runs for a short period with starting fluid, you can rule out a timing and mechanical problem. I'd guess once the motor gets turning, it creates enough vacuum and compression in the cylinders to fire on either a weak spark or low fuel.