I'm sorry if this has been discussed before, I did a search and couldn't find my situation.

So, I have a 1994 f150 that I swapped a low mile 4.9 into. It's been running "good" I would say, up until about 4 weeks ago, right around the time it started getting cold here in Ohio. By good I mean it's never really had the grunt I remember from my 96 with a 4.9.

Anyway, to the right now issue. I started feeling a loss of power right around 2k rpm. No stuttering or misfiring. I honestly thought it was pulling time (It might be? You can't exactly do logging on OBD1, lol) But after talking with another mechanic friend, they said to check fuel first. So I went and grabbed a fuel pressure gauge. That's were I'm getting caught up.

Everywhere I look I get different information about these engines, so I'm just gonna give as much information that I can think of, and see if anybody can fill in the blanks, or help me out.
Fuel pressures are as follows: KOEO, 35 psi. KOER, bouncing between 45-48. FPR no-vac, the gauge just starts bouncing like mad between 40 and 60 psi.After I turn the key off pressure climbs to about 55, then starts to drop very slowly. If I take it for a drive it'll bounce between 25 and 65 like crazy under load (see attachment, sorry about the quality, the gauge is sticking out of the hood). This is an oil-less gauge Some say it's "normal" for oil-less gauges, others say not. I would think this is not normal, but I don't really want to be throwing parts at this hoping the next one will fix the issue.

I did a DIY balance test. Clamped throttle at around 1800 rpm, and pulled each injector connector. Every one made the engine stumble. So, I assume they are fine.

I've never seen this scenario before. The FPR isn't leaking gas. My opinion is that the fuel pump is failing, and can't keep up (which may also be leading to lean-knock, causing some KR). But, I wanted to get others opinions. Any insight would be greatly appreciated.

 

Nice job on the diagnosis. Definitely strange behavior. The fuel pressure regulator is working backwards. KOEO should be higher than KOER.

I'd say your fuel pump is toast. Very common for these vehicles of this age. I'm sure a new, hi quality pump will fix your problem. If you have the funds, try to get a motorcraft pump. They're expensive, but the last one lasted 28 years. Aftermarket are hit and miss. Delphi is the next best pump for 1/4 the price. Just make sure you test the pump and sending unit before you install it in the tank and button it up. Some folks have had problems with defective units and it drove them nuts trying to diagnose it.

 

Thank you Prototypemech. I have been going crazy, not wanting to pull the parts cannon trigger, lol. I am gonna try to get the motorcraft for sure, if I can work it into the budget. Thank you for the recommendations and expertise. It is greatly appreciated.

 

Just updating in case somebody comes across the same issues. It was the fuel pump. Wound up not being the original. Somebody picked up an "Airtex E2064MN". Unfortunately I couldn't replace it with Motorcraft, but I did at least go with the Delphi. Goes straight to 60psi as soon as I pull the regulator vacuum now.

No surprise, now that the engine isn't starving for gas it has a lot more power (much like my previous 300). Definitely running rich when I get on it. I'll probably pull a battery terminal to reset fuel trims tomorrow. As of right now, I'm just happy the fuel pump took care of the issue.

Thank you again, your help is greatly appreciated.