Lo or hi pressure fuel pump issues?

[BoomTexan]

Hey yall, been having some unusual symptoms with my truck recently. Just replaced the distributor so I thought maybe I timed it badly, but at this stage it doesn't seem like that, more like a fuel delivery problem.

I'd like to put my hypothesis here and just see if this lines up with yall's estimation. My guess is it's a failing low-pressure pump, but I'm not sure if I should replace the high pressure one as well. 1.) Have to stomp on the throttle a little to get it to start, adjust the idle speed really high.
2.) When I make hard right turns, I get some fuel cutoff happening. Thought the tank might be crushing a fuel line up against the frame rail or something, but I hanger strapped it really tight and the issue continued.
3.) Drove ~100 miles and once I reached highway speed I noticed I could only keep around 75 flat out, where I was getting 85 earlier. Had it pinned for a bit and noticed that at higher throttle it was starting to surge and be unable to keep speed. The higher throttle issue kept creeping lower and it got to a point where I was hitting maybe 30mph up hills barely able to keep it idling. Made it to a gas station, freaking out, called my friends to see if they could pick me up. Got in my truck and thought I'd try and hit the backroads and get a little ways back, and after 15 minutes of sitting, the issue was mostly gone and I could hit like ~65. On my way back, ended up making it like 15 miles, dropping to 50mph, then letting it sit 15 minutes and keeping going. Seen other people saying that this might be due to the high pressure fuel pump still sucking fuel through, then overheating and not being able to keep going.

Do yall think that I might've damaged my high pressure fuel pump by overheating it a couple times, or that this makes sense? I'm installing my spare lo-pressure pump today anyways just in case, but just wondering if yall have had similar issues.

 

[alwaysFlOoReD]

Fuel filter?

 

[BoomTexan]

Fuel filter?

I just replaced my fuel filter a couple weeks ago. I can absolutely check it, but I would be extremely surprised if that were the issue. I'm also wondering why the issue with surging would be a problem, and why it would only materialize after ~45 minutes or so of driving. Seems like it would be more of an electric motor issue.

I've heard of bad parts from the factory, but oil and fuel filters are generally completely fine in my experience.

 

[alwaysFlOoReD]

So on old style mechanical pumps there is both a fuel pressure and fuel volume to test for. I imagine that it's the same with both the low pressure and high pressure pumps. The frame rail pump isn't hard to get to and could be removed for testing fairly easily. If it passes then do the low pressure pump.
Also, I've had problems with the electrical connections at the frame rail pump. The spade connectors seem to lose tension and replacing those has fixed up that problem on numerous trucks I've had. Might want to check that while you're in there.

 

[Curious Hound]

I'd recommend testing fuel pressure with engine running. Make sure it maintains minimum at all rpms.

 

[Shran]

I had many low pressure pump failures back in the day. I'm not kidding when I say like at least 10 in one truck - they would last 6 months to a year and just stop working. I always knew what was happening because the truck would just suddenly start sputtering and shut off. Sometimes I could get it started if I waited a while (the high pressure pump would definitely get hot and lock up temporarily...) but mostly it was just dead until I replaced the pump.

I also had a high pressure pump get really weak in my F150 and it would sputter under low and up hills.

The ultimate fix in my mind is to delete that ridiculous setup and use a pump from '89-? in the tank. Probably no newer than like 92/93, the pumps got taller at some point and don't fit in the sending unit without modifications. KEMSO pumps on eBay have been excellent, I have not had one failure there in many miles and years. There is some plumbing involved in the swap, so plan on building fuel lines and tracking down fittings but it's not real difficult.

Of course it could be something else, as everyone above has suggested, test first before you replace any parts.

 

[lil_Blue_Ford]

I had many low pressure pump failures back in the day. I'm not kidding when I say like at least 10 in one truck - they would last 6 months to a year and just stop working. I always knew what was happening because the truck would just suddenly start sputtering and shut off. Sometimes I could get it started if I waited a while (the high pressure pump would definitely get hot and lock up temporarily...) but mostly it was just dead until I replaced the pump.

I also had a high pressure pump get really weak in my F150 and it would sputter under low and up hills.

The ultimate fix in my mind is to delete that ridiculous setup and use a pump from '89-? in the tank. Probably no newer than like 92/93, the pumps got taller at some point and don't fit in the sending unit without modifications. KEMSO pumps on eBay have been excellent, I have not had one failure there in many miles and years. There is some plumbing involved in the swap, so plan on building fuel lines and tracking down fittings but it's not real difficult.

Of course it could be something else, as everyone above has suggested, test first before you replace any parts.

Same stuff I’d recommend. When I ever get back to working on my 88, I’m going to new fuel lines, plastic tank, and 89 pump. I believe you have to use the fuel sender from an 88 or older to get the fuel gauge to work right but 89 changed to a high pressure in tank pump and that simplifies things.

Both my 89 and my one 00 have sprung fuel line leaks. The 00 ended up getting patched like 6-7 times before I got fed up and replaced it all. I learned from that.