SPCMarty

Can anyone offer an explanation why my truck, 5.0, coughs at speeds below 38mph or so? It's bad enough I can feel the truck jerk while driving and hear the engine miss. Once I get cruising faster it goes away.

Anyone know if these f150s had their frames drilled/setup for towing packages regardless if it ever had one installed?

djhives

If its missing then theres an ignition issue - have you done your wires, plugs, checked your distributor and set your ignition timing - that's where I'd start if I felt an ignition misfire

Bibo1985

Don't know about the tow package, but I've got a 4.9 giving a similar problem just in the lower speed range of each gear. I'm testing the TPS tomorrow, after that, I was pointed to look into the ignition module? Dunno for sure what the cause is, honestly feels like the clutch is slipping in mine.
I'm having a little trouble interpreting what you mean by cough, but I'm assuming we're having similar issues here? Feels sorta like the trucks bucking the way it does not giving it enough gas starting off?
Another thing to check (not sure if yours is manual or auto) is tranny fluid. I'd just topped mine off, then figured out it wasn't level when I did so, so it overfilled. Not sure if that was relevant, but it did seem to slightly improve after the level was corrected.
Just a thought, if you give it just a little throttle, does it stumble at first?

Bibo1985

Those are good starting points as well, didn't think to mention em because I've sorted through all that on mine

SPCMarty

When I got the truck I replaced all the usual ignition parts, MAP sensor, some module on the driver side fender, coil.
Bucking would be a good way to describe it.

Bibo1985

Here's what I trie today.
I attempted to test my TPS, couldn't get a reading. I called my parts/tech guy, told him the situation which he's been trying to help from the beginning.
Anyway, went by there, couldn't read any codes (think my plug is outta whack) so tried the shade tree method; if it meters air or fuel, unplug it while running, idle goes to hell, it's at the very least operational, give light throttle, see if the stumble remains. Tried the MAP vacuum/plug, TPS, EGR control valve, Fuel pressure regulator... all caused idle problems and kept the stumble w/ light throttle, which was good, but, the fuel pressure regulator... unplug the vac line, block the intake port, gave it a lil throttle, idled up with no stumble. Of course, this is NOT the recommended test methods. But my thinking (could be wrong) is the FPR is either worn out, requiring more vacuum to function hence the stumble, at least me thinks.
I'll have a new FPR Wednesday, so I'll give an update then.

farmer12

Get a fuel pressure guage on there and see what it's doing.

Don_H

38 mph is about the exact speed the transmission is fixing to shift into high gear. If you're right at the shift point, its possible the trans is upshifting and downshifting giving you the jerking feeling.

Bibo1985

Planning to hopefully this week, just gotta lay hands on a tester.

BBS_Jeff

You guys all missed it... he's driving slow, PICK UP THE PACE GRANDMA!! Lmao. :-)