I have a 1991 Ranger with a 2.9 l engine. The problem I have started around 2 weeks after I replaced a bad fuel pump. It will start, after I crank it for a while and after it begins to fire, I pump the accelerator to keep it going. If I let up on it, it will idle down rapidly and sit there running like it is hitting on 2 or 3 cylinders and then die. If I remove the hose from the intake manifold and spray starting fluid into it, it will start and run perfectly until the starting fluid is used up.
I have replaced the fuel filter, dist cap and rotor, plugs and wires,and the new fuel pump came with a new strainer. It was an assembly that I just dropped in to replace the defective unit. If I do a pressure test, it will read around 40 psi but I have questions about that too. I would think that if I depress the relief button on the pressure tester while the pump is running, it would run gas out and continue until I shut the key off. It doesn't do this. It lets a little bit of gas run out but the pump shuts off like it has built pressure and the gas just trickles out, and the pump never kicks back on. Maybe this is a clue for someone who knows more about this system than I do. This may be normal. If I disconnect the braided hose that comes from the fuel tank, the pump will run until I turn the key off and it seems to have a lot of pressure and volume. Any help would be appreciated.

 

The fuel rail pressure should be about 40 PSI by keying on the ignition w/the engine off and about 30 PSI with the engine idling. When you turn the key to "ON" but don't start the engine, the pump will only run for about 1~2 seconds to pressurize the rail and then shut off. It starts running again when the PCM sees crank rotation.

 

That explains why it doesn't continue to run fuel out. Thank you. Any thoughts on the sluggish running?

 

Since it responds to starter fluid, I would guess:

Dirty injectors;
Vacuum leak; or
Low fuel pressure while running



I'm not sure but I suspect that your engine is speed density, bank-to-bank injection. If so, that opens up a couple more good possibilities:

Open PCM injector wire to one cylinder bank (actuates 3 of the 6 injectors); or
Bad Manifold Absolute Pressure (MAP) sensor

 

I have been thinking that the issue revolves around the injector system. I can replace the MAP sensor and see if that helps if you think it may be the culprit. I think it's the original. I have owned this truck since it was new.

 

Actually, I think that the MAP is the least likely of the things I posted. I would check the wiring from the injector harness to the PCM - I have heard that having one bank (3 cylinders) out because of the injector wiring is a known problem with the earlier Ranger sixes.

 

Thank you Bob. I'll check the wiring first.

 

I wanted to post the final solution to my rough running problem. Remember, I replaced the fuel pump early in the history of the problem. What I found out was that I didnt have the new pump sealed very well and water leaked into the tank. I was trying to burn a gas/water solution that dont work very well. Remember that if you replace your fuel pump, seal it well. Thanks for all of your help.

 

Good info. I wouldn't have guessed that one.