Mancomb

I have an AT 1990 F150 XLT Lariat with ~146k miles on it; it sat for over a year @ my parents' house, and when I picked it up, it ran really rough. Over time, I repaired (or had repaired) several issues, which helped the truck run better, but it still has a few issues, which I've noted in the title of this thread. Basically, what I'm experiencing is an intermittent sputtering or stuttering, similar to when the RPMs drop too low for the gear you're in in a manual transmission vehicle and the car wants to stall, but it only happens for a second, and it seems to happen whenever the transmission shifts up a gear, and the RPMs drop; and it seems to happen at most speeds, but more often between 30-45 MPH, and when I'm climbing a hill or driving on the freeway (I'll usually need to depress the gas pedal a little more in order to make it downshift so that I can accelerate on the freeway; otherwise, it starts to sputter).

I've thought of a few different areas that might be affecting this, including the engine electrical and fuel delivery systems. Below is a list of things I have replaced (or have had replaced) in the hopes of fixing the issue, and each time it has slightly increased the performance, but not completely fixed the issue:

• Tune-up (replaced distributor cap, rotor, wires, and plugs)
• Replaced fuel filter
• Had 1 fuel injector (on #5 cylinder I believe) replaced; that significantly helped, but didn't fix the issue
• Replaced electric fuel pump inside front tank
• Replaced ignition coil (this caused the idle while in PARK to drop significantly; you almost can't even tell it's running)

I had also replaced the alternator several years ago, as well as the exhaust from the Cats back to the tailpipe more recently, though I don't think those would really affect the issue at hand.

Other than that, (and the air and oil filters, of course), I believe everything is OEM that is still on the truck, including the other 7 fuel injectors.

I've been thinking about a few other things that might be causing the issues I'm having, including clogged/deteriorated fuel lines, a bad air flow regulator, and a bad ignition module. I've been thinking of taking it to a shop to see if they can pinpoint the problem(s), but depending on how long it takes, I could end up spending a hefty chunk of change for just a diagnostic.

Any ideas or advice would be greatly appreciated; this is killing my fuel economy, and is doubtful good for the truck either.

If there are any questions, please feel free to ask. If I have missed something, please feel free to point it out or ask about it, and I will endeavor to add anything I might have forgotten that I remember later.

Rmehuron

fuel pressure regulator?

Rmehuron

of course check ur fuel filter too!

Mancomb

I think my dad mentioned something about the fuel pressure regulator, and given the symptoms, that might very well be the problem (or at least part of it); of course, I've said the same thing for everything I've done thus far, so it might just be one of several issues. Thanks for the idea, though; at least I have a good place to start now.

Also, I was thinking about checking the fuel filter again, as you said, since it's very possible that, even though I've replaced it once, it might have been gunked up again very easily; especially since the bad fuel economy has me getting closer to empty on my tanks than I prefer, which could cause a lot of the crap in the tanks to clog up the filter/fuel lines. Thanks for the response, Rmehuron!

Maxw3lll

Weird... I have almost the same exact truck, '90 XLT lariat 4x4 with 150k, and the same story (sat for a few years), with the same exact problem... it would be really nice to know what it is!!! That's pretty crazy. I have been running injector and fuel system cleaner through it each time I fill up in hopes that it will help the problem but it hasn't. I thought giving it a tune up would help and I'm doing it tomorrow but after reading what you said about it not helping, it just makes me more puzzled....

Jeeez

Maxw3lll

Mine sputters between 35 and 40, and also at freeway speeds, 55 - 65

Mancomb

Yeah, I tried the cleaners as well, several times in fact, and it helped a tiny bit, but not much. The tune-up helped other issues, but not this, unfortunately.

Yeah, that's exactly what mine does. After talking to my dad earlier today, we surmised that it sounds like a fuel pressure issue, and that it's under-pressured, which would explain the sputtering. I'm going to set up a time with my dad to go down to his house and replace mine; I think I'll check the injectors while I've got the manifold open. If you want, I'll let you know the results after we're done, though it might be a little while yet. I found the part online on NAPA's web site for $32, and I think the hardest part will be removing and replacing the upper manifold.

Maxw3lll

Sure sounds good, man.

So you're replacing the fuel pressure regulator? I will see what the shop foreman at a big dealership that I work at has to say, I'll talk to him tomorrow. A problem with the fuel pressure definitely sounds like it could be the problem. I will let ya know what the mechanic says.

Maxw3lll

I started another thread on the older f150's forum section, too, btw

Maxw3lll

Checked with my mechanic and he said that I should do the tune-up before I started with anything else. Turns out, that's exactly what it was! The plugs were in pretty terrible shape and now she drives like a dream. Maybe check your plugs if they haven't been replaced in awhile...? Best of luck, man.