I have a 1989 ford f-250 5.8l that is having fuel pressure issues. I have replaced the rear in tank fuel pump it was bad. (the front tank is deleted), high pressure fuel pump it was bad also,fuel filter, fuel pressure regulator, fuel pump relay,cleaned EGR valve. The issue I am having is that it loses fuel pressure under throttle. At idle it’s running 35-36psi and when you crack the throttle it drops down to 22-24ish. It stumbles and it’ll back fire inside the intake and it’s just sluggish, feels like it has 0 power when accelerating because it doesn’t. Could vacuum lines or something of that nature be an issue?

The brake booster seems to be bad, the brake pedal goes to the floor I can pump it builds pressure it seems but loses whatever vacuum it had once released. I just don’t know if that would cause a loss in fuel pressure. I can pull the line that is from the intake plenum to the brake booster it revs up high it’s sucking quit hard I put my finger on the line it’ll about kill engine put it back on it idles it’s just kinda a rough idle.

It has a tank selector switch still on frame rail and I want to bypass it all together I’m wondering if that could be a problem?

It use to run fine,I parked it and haven’t drove the thing close to 6 years now.I hate the ford fuel lines, can I rip all that stuff out and just use your standard black gas lines with hose clamps? Any input is helpful and appreciated I know there’s a lot of knowledge in this group and I’m fine with throwing whatever at it because I like the pickup I’ve had it since high school. Thanks

 

Before we do anything, let's make one thing clear, those fuel lines are under pressure and that is why they use special line and clips to secure them.Hose clamps will not do the job. You need to stay with what was used when the vehicle was built.
You found the problem of inadequate fuel pressure when throttle is opened, the idea is to now find out why..
We need to make sure the fuel pressure regulator is not defective. If you clamp the return line to restrict it , see what you get when the throttle is opened.

If the pressure still drops the problem is the fuel pump. If it holds the problem is the regulator.
Anytime the brake pedal goes to the floor, plan on replacing the brake master cyl. It has to be bench bled before installation.
There is a good possibility of a vacuum leak. If you carefully spray some brake cleaner around the vacuum areas,it will pull in the cleaner and idle speed will usually increase and level out.. Let us know how you make out with all this , OK, thanks.

 

I have sprayed brake cleaner around most if not all vacuum lines, it seemed to barley idle up when I got around the pressure regulator.that was about a week ago, the pressure regulator was missing 1 out of the 3 screws. I replaced it along with pressure regulator I will check again. I can hear a humming noise from a vacuum pump or something, it has a white and green vacuum line going to it and it sits right next to the coil. I have no ideal what those do but one line (green)goes to the EGR valve. Is that thing worth switching out? I guess I’ll m not worried about the brakes or the brake booster right now as long as that can’t have anything to do with fuel pressure, that’s a whole other ordeal I’ll get to after the fuel hopefully.I’m in the middle of taking out the tank selector switch I don’t want any interference with fuel in and out. The reason I asked about the fuel lines is I want to change the lines from tank to the inlet of the high pressure pump after that it’s little sections of hose from pump to filter and so forth I’d leave. The line that comes out of the outlet side of the filter makes a big loop and heads up to the fuel rail and it has like a rubber sheath around it. To me it seems like it could possibly be pinched flat right there at that loop I’m gonna take that off and give it a once over also. I know i’m all over the board here but this thing had really old bad gas and I was thinking about changing out the injectors also. How often do those go out or get clogged? Do they have little screens in them also. Thanks a bunch.

 

I seemed to have fixed the fuel problem I got rid of the fuel switch and went over the lines and the return line was kinked. Now when the truck is cold it will run great all the way until the truck warms up and now it just basically just runs terrible. I’ve went over this the last 2 days and everytime it’s the same outcome right when it gets warm and the guage reaches the point to wear the thermostat would open it just loads up almost like spark issue. It does not have a check engine light on and the check engine light does work. I had a problem at the beginning of the year where I had wires that where a ground wire that bolts to the chassis by passenger headlight and a positive off the battery rubbed together and melted the wires. I got it fixed but I’m wondering if that messed up a computer,Distributor, coil? It was dead in the water until I started at the battery and started peeling back the wire loom.it’s hard to diagnose beings it only happens while driving and being warmed up. What should I look at?

 

The better thing to consider would be to have a shop with a capable scan tool and check the data stream info . BOTH, cold and hot , (operating temp approx 140 degrees F).