'94 4.0 stutter off idle

[Slysdexia]

My '94 Ranger has a rather persistant stutter/hesitation whenever you give it quick throttle input (repeatable every time), or load it up below 2,000RPM (less consistant) ie: backing it out of the driveway, you can hear it constantly misfire, and up hills it can start missing pretty badly unless I reduce throttle input. The issue just seems to be with quick input, as full throttle is just fine on flat ground as long as I roll into the throttle, rather than mash it.


Coil pack looks to be original, fuel pressure regulator looks original, I changed the fuel filter soon as I got the truck, so that's not a likely issue yet. Disconnecting the vacuum line to the FPR didn't do anything appreciable, MAF wasn't very dirty, but I cleaned it anyway, reset the computer, still does it.

My list of possible culprits lies in the MAF, coil pack, FPR, or plugs, though they and the wires seem pretty fresh (plugs moreso than the wires). No EGR system at all, so that's not a possibility.

Truck has 128 indicated, it had a broken speedometer cable when I got it because it had been routed wrong, so there's no telling the true mileage. My guesstimation is between 160-280k. No idea on the history of the truck other than it was dragged through rivers, judging by the state of the power steering fluid, radiator fluid, and the 20 pounds of sand, fine gravel, mud, and oak leaves under the bedliner, not to mention two mouse nests.

 

[kevmurray]

i know when i had a prob going up hills an it sounded like it was miss firing it was really back firing threw the exhaust becuase i had low fuel pressure because of a bad fuel pump do u run in on empty alot? a tune up prob wouldnt hurt either

 

[AgPete139]

Using brake cleaner to spray the MAF, wait until it dries, and reinstall will usually yield positive results.

Code 128 is a coolant temperature sensor, and that may be bad on your truck if you want your CEL to go away. I doubt its the FPR, coil pack, or the plugs, but the plugs are worth removing to see how worn they are.

It sounds like it's still an even idle despite the stuttering.

 

[Slysdexia]

i know when i had a prob going up hills an it sounded like it was miss firing it was really back firing threw the exhaust becuase i had low fuel pressure because of a bad fuel pump do u run in on empty alot? a tune up prob wouldnt hurt either

It doesn't really sound like a backfire, you can just sometimes hear it running on 4 or 5 cylinders backing out of the driveway or up hills. No backfires, except once when I stomped on it.

Using brake cleaner to spray the MAF, wait until it dries, and reinstall will usually yield positive results.

Code 128 is a coolant temperature sensor, and that may be bad on your truck if you want your CEL to go away. I doubt its the FPR, coil pack, or the plugs, but the plugs are worth removing to see how worn they are.

It sounds like it's still an even idle despite the stuttering.

By 128 I meant 128,000 miles. The CEL isn't on, though you'd think it would be.

I've already cleaned the MAF, and it didn't change anything. The plugs look to be very fresh, but I keep hearing that cologne v6s can be very sensitive to their plugs, and these aren't Motorcrafts, so I suspect they may be part of the issue. The coil pack is original equipment, 16 years old, and this truck has been nose deep in muddy water before, that's why it's on the list.

 

[Slysdexia]

Well, I've REPLACED the MAF, it still stutters like living hell under load under 2,000 RPM, sometimes above it. It's damn near perfect with the MAF disconnected. Can I actually et some HELP here?