Hesitation/Acceleration Problems - F150

[Twister]

I know its not a ranger but i need some help with my f150.

So today my 97 f150, 2wd 5.4L automatic has started giving me some troubles. The truck has 291k miles on it, i bought it with 260k miles on it. About a week ago the truck overheated due to a busted radiator side tank, it was promptly replaced the next day and i have had no problems with it since, till today. Sometimes when you start it it will stumble alive like its out of gas, give it a sec and it settles down. When you get going, its a little down on power, i know it has 291k miles on it but it pulled hard. Its OK till you get to about 35-40, when it just stops accelerating. I had my foot to the floor and it barely went above 40, if you ease into it slowly it will slowly accelerate till about 45, drop down to 40 and then go like normal.

When i changed the radiator i lost about a cup maybe a cup and a half of transmission fluid, i havent gotten time to replace it but i didn't think that small amount of fluid would dramatically change performance, the fluid also looked almost new. The only other things i have done to the truck is some brake work and replace the alternator. I have no knowledge of what the previous over did or did not do.

It is not throwing any code, and the OD light/button is broken, i think on newer rangers the OD light would would brink indicating transmissions problems, not sure if its the same on these trucks.

Any help would be very appreciated.

 

[Twister]

Added one cup of tranny fluid, took it around the block and checked the level. It wad smack dab in ghe middle of the hot part of the dipstick.

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[RonD]

Couple of things to check.
You could be getting too much fuel or too little fuel.

Too little fuel would be the fuel filter, usually a $10 part and not to hard to change, and well worth it in the long run.

Too much fuel could be the FPR(fuel pressure regulator), this is on the fuel rail and has a vacuum line attached, if the diaphragm on the FPR develops a leak, the leaking fuel is sucked into the intake, so starts to flood out the engine.
Not sure which year the F-150 switched to returnless fuel rail, maybe '98

I would think either of these would set the CEL, lean or rich.


When did you get gas last?
And could it have had water in it?

 

[Twister]

Any tips on grtting the fuel line fitting off the front of the fuel filtet. Its got a smaller fitting than the back, I've brrn messing with it fir 1 and a half hours to no avail. The back one.come off in a heart beat but not the front one.

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[RonD]

Google: ford fuel filter tool images

Some of the fittings require you to slide something in under the connection to release the catches.

Also did you relieve the pressure in the system, at the fuel rail, pressure could be holding it too tight.

I have cut up an old anti-freeze bottle, hard, but not brittle plastic, rolled it and then slide it in and used a screw driver to push it in, to release connection

 

[Twister]

Google: ford fuel filter tool images

Some of the fittings require you to slide something in under the connection to release the catches.

Also did you relieve the pressure in the system, at the fuel rail, pressure could be holding it too tight.

I have cut up an old anti-freeze bottle, hard, but not brittle plastic, rolled it and then slide it in and used a screw driver to push it in, to release connection

Yeah I had a tool for releasing the clips and I broke it lol. Gotta buy a new one tomorrow.

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[Twister]

Changed fuel filter, it had no improvement. Got out my fuel pressure tester. Hooked it up, with key on, key off, the max i could get it to was 22 psi. So i started it, still only 22 psi, revving it and it stayed at 22 psi. So to make sure the gauge wasn't bunk, i put it on my 87 Bronco ii. With Key on i instantly got 40 psi, and running i got 35 psi.

 

[RonD]

yes, 22psi is too low, 30-40psi would be spec

Did you unplug the vacuum line on the FPR(fuel pressure regulator) while gauge was hooked up?
Pressure should jump up when you do that, if FPR is working, if it doesn't jump up then replace FPR, it is stuck open.


At idle engine vacuum is high and fuel use is low, so FPR is held open by the engine vacuum to return fuel to tank, as you drive the vacuum decreases so FPR closes holding fuel pressure up when more fuel is being used.
Simple system but works fine, if FPR is working

 

[Twister]

yes, 22psi is too low, 30-40psi would be spec

Did you unplug the vacuum line on the FPR(fuel pressure regulator) while gauge was hooked up?
Pressure should jump up when you do that, if FPR is working, if it doesn't jump up then replace FPR, it is stuck open.


At idle engine vacuum is high and fuel use is low, so FPR is held open by the engine vacuum to return fuel to tank, as you drive the vacuum decreases so FPR closes holding fuel pressure up when more fuel is being used.
Simple system but works fine, if FPR is working

I didn't unplug it, I will try that tomorrow. Thanks

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[adsm08]

I would be looking at the pump right now.

 

[RonD]

yes, fuel pump could be the issue, even low voltage at the pump, or clog screen in the tank.

hopefully it's the FPR

 

[Twister]

I would be looking at the pump right now.

I forgot to mention it is kind of hard to start. With that symptom would that point to fpr or fuel pump?

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[Twister]

With the fpr unplugged I still only get 22psi

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[RonD]

Could be either.
Fuel pump has a check valve that prevents fuel from flowing backwards when pump is off, which it is a lot on Fords, this holds the pressure in the system.
FPR is at the other end, it holds the pressure the pump creates.

FPR is just easier to test, than dropping the tank or lifting off the bed.

 

[RonD]

With the fpr unplugged I still only get 22psi

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So with engine running fuel pressure was 22psi, and when you removed the vacuum line it stayed at 22psi it didn't jump up and then drop down to 22psi?

If so I would replace FPR.

Still could be fuel pump but FPR reads bad if it's not effecting pressure.