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Old 10-27-2009, 10:44 PM   #1
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Default 1991 F150 Significant Power Loss

Okay, so it still goes. I was having some serious power issues before, then the smog pump went out, the serpentine belt snapped, and I've since replaced the pump and serpentine belt.

I've also replaced the muffler, pipe, o2 censor, plugs, cap, rotor, wires, and fuel filter.

It was running rough at start up before I changed the pump and everything else (which the pump is the last thing I replaced that appeared to fix my problem - temporarily), and then it ran STRONG for the weekend.

After a nice, long test drive, I started noticing it sputtering, idling just fine, but when I put it in gear to give it gas, it just does not want to go.

I can put it in first (which is a granny gear on this model), I'll get the RPMs up, shift into 2nd, and 2nd will be fine until I (finally) get it up to about 25mph. Then the truck will shake until I shift into 3rd, which will eventually get up to about 30 or 35 if I'm on flat ground - any slight hill, and I'll have to downshift to 2nd and deal with the sputtering - and then 4th will maintain.

I'm pushing the engine so hard, it started to really heat up a couple of times, and when I noticed that, I stopped driving it. Now I'm still without driving and for the life of me, I can't seem to figure out what's going on.

Feel free to ask questions, but please help me get this thing figured out. I know I can't be far from the solution.
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Old 10-27-2009, 11:04 PM   #2
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fuel pump?
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Old 10-27-2009, 11:06 PM   #3
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could be the timing, one of your plug wires have come off, bad gas, or like what m8r8j said, fuel pump.... when you say "shaking", do you mean, missing? or vibrating?
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Old 10-27-2009, 11:07 PM   #4
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id guess something with the fuel, maybe the injectors are plugged
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Old 10-27-2009, 11:27 PM   #5
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Switch between gas tanks --- same problem?

If the problem changes it's probably the low pressure boost pump located in the respective tank

If no change, probably need to check fuel pressure and the high pressure fuel pump located on the frame rail.
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Old 10-28-2009, 12:29 AM   #6
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Well, I've been running on the back tank exclusively for a while, and have been running with the front take at or close to empty. All the wires are fine, and it idles and (seemingly) revs just fine. I honestly don't even know where the fuel pump is on this bad beast. I'm not a mechanic by long site, I just do what I need to do to keep my truck running the best I can, because I freakin' love it.

How would I go about checking my injectors? It seems to only have the problem when driving, and I'm certain that it's not the transmission.

When I say shaking, I guess I should have said jerking... When I'm in 2nd at about 20-25, and depending on the grade of the hill I'm going up (these are in town hills - VERY mild... I could bike up them faster) is when it will start jerking. Now, I can shift up to 3rd, but when I do, the RPMs go up, and the MPHs go down - but it stops jerking and just works the engine.

It's seriously confusing - Could it just be a balance of fuel, or air in the lines?

By the way - I am burning through s***loads of gas.

Thanks for all the insight... hopefully that provides a little more information...
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Old 10-28-2009, 01:26 AM   #7
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First of all, check the computer for codes. This thread explains how: http://www.f150forum.com/f10/how-retrieve-trouble-codes-obdi-10907/
Post any codes here and we can go from there.
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Old 10-28-2009, 09:13 AM   #8
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When my rear tank fuel pump went out it jerked a little but it had that distinctive feel of running out of gas. And it would stall out even at idle. I would check your plugs and wires. I've had a bad wire, and it didnt act up bad until I got in the higher rpms and in about 2nd or 3rd gear then it jerked like the transmission was ripping apart.
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Old 10-28-2009, 09:15 AM   #9
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Easiest way to check if its the injectors is unplug them one at a time while running. If it gets worse with one unplugged, then it was working before. That's how I checked mine, it was the easiest way I could think of, and I doubt it hurt anything.
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Old 10-29-2009, 05:36 AM   #10
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My guess is a bad fuel filter or maybe even the fuel pressure regulator. the easiest way to check the regulator without buying tools is to start the truck and remove the vacuum hose attached to the FPR. Wait a few seconds and see if fuel starts coming out of the nipple where the vacuum hose goes. if it does then it's bad, if it doesn't then it's most likely good. however, there is a possibility that the screen in the FPR is covered with crap and not letting the fuel flow like it should.

Last edited by flareside_thunder; 10-29-2009 at 05:41 AM.
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Old 10-29-2009, 05:36 AM
 
 
 
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