I have a 1990 F250 with a 5.8 and automatic tranny.

Engine starts and idles great,
Runs cool at the O on Normal,
Gets 12.8 mpg
Shifts smoothly most of the time

I have a pretty long hill on the way to work, and on the way back it's steep. Lately I lose power when I hit the hill. I give it gas and the engine sounds like it's trying but it slows down. Even if I floor it and it downshifts it still does t gain speed. I changed the fuel filter and it seemed to help for a week or so, then it started doing it again. I changed the oil and took it for a test drive and it seemed to be normal. I floor it and it gains speed no problem. The next morning I let it warm up on my way to work then try flooring it. No power. Up the hill I could go no faster than 25mph at 1800 rpm without it feeling like it was trying way to hard. I disconnected the cat converter and put some wedges in to see if it would solve it and it doesn't appear it has. I did a slight hill and couldn't pick up speed without flooring it and downshifting. I am pulling codes tonight but I am wondering what I can rule out? Can it be a clogged cat of it comes and goes? It doesn't jump or chug or backfire. It doesn't miss. I will check fuel pressure tonight but it sounds like it's getting fuel when I give it gas, there's just not a good enough response. Any ideas or thoughts would be appreciated. I am learning about my truck and your input would help me gain the knowledge I need to fix her. Thanks.

 

First guess is fuel pump fading out on you. Check that fuel pressure.....

 

I was thinking a fuel pump would be good or bad. Do they break down slowly sometimes? I'll post the results in a few.

 

I checked the fuel pressure. Engine off it would consistently go to 15 psi. If I turned the key off and on again it would go up to 40 and seemingly stop itself at 40. If I kept turning it off and on it wouldn't go passed 40. Retesting it would always go to 15psi the first time. Engine running it would sit at 40 psi steady.

I also did an EEC self test.

KOEO - 34

KOER - 44

Any ideas what could or could not be thr problem?

 

I should note that the catalytic converter was unbolted during the test because I wanted to see if that would help on the drive home. It still felt sluggish and I think this might be why I got code 44. Am I right?

 

The fuel PSI at idle should be in the 35 PSI range with the vacuum line attached. Removing the vacuum line should result in the fuel pressure increasing to 40-45 PSI.

Assume Code 34 was actually a stored code (CM) and not KOEO? CM code indicates the EVP signal intermittently failed above the closed limit of 0.67 volts.KOEO indicates the EVP circuit is above the closed limit of 0.67 volts.

Code 44: Thermactor Air Injection system inoperative (Right side) has nothing to do with the converter being unbolted. That indicates the AIR injection system has a failure. Could be a vacuum hose or leaking AIR injection components.

 

I don't put much faith in no-load fuel pressure tests. Tape the gauge to the windshield and get a load on that motor. I worked on a Tundra over the summer that was perfectly in spec in the driveway idling, but dropped to 20psi under load and went scary lean @ 18:1 on the wideband (not OK under load). It completely fell on its face at that point too.

 

Everyone seems to have zeroed in on fuel delivery being the issue. You may have a vacuum leak...

 

Possibly the "sock" on the fuel pump is clogged, or the short length of hose attaching the pump to its bracket is leaking, or you have a faulty fuel pump or pressure regulator.

As suggested, a pressure gauge plumbed in to monitor fuel pressure while running is the way to go for diagnosing while driving.

I made up one by silver soldering a tube fitting to a brass Schrader cap and attaching to the fuel rail. Then I ran the tube to a gauge laying on the instrument panel so I could verify that the pressure dropped when the engine hesitated.