2.9 Very Intermittent Stumble

[mihulka3]

MY 1988 Ranger Extra Cab 2WD 2.9 Auto did something interesting coming home for from moms the other day. I had the cruise on and the truck felt like it hit a small speed bump for a split second. I turned off the cruise and kept driving and about 20 miles later it did it again. The truck 99.9% runs fine and starts fine. It's not perfect but fairly smooth. The motor has less than 1k on it. I'm thinking the fuel filter may be clogged or the high pressure pump possibly bad. Could it be a sensor issue. Maybe a TFT module? I'm on my third TFT since 1998.
The truck sat for about 1 1/2 years getting the work done. Fuel in tank could be a contributing factor although it sat almost empty when truck was finished.
I also need to recheck timing. The truck pings some under load and never did that prior to replacing engine. If the TFT is going bad the truck is going into river. I have had it with the issues. Any help would be appreciated.

 

[Big Jim M]

Very good description of a clogged fuel filter. Change it and see! All should be good.
Big JIm

 

[RustedRanger]

Run some strong injector cleaner, Lucas or STP Concentrated works well. I'm not saying it will fix the problem but it can't hurt and will help remove some build up in the fuel system. Gas now a days goes bad really quick compared to how long it used to. I bought a 86 Marquis several years ago that sat for a long time and it had chunks of what looked like wax in the tank that clogged the fuel pump and killed it. When I changed the pump I drained out as much gas as I could,put in some injector cleaner and fresh gas and never had any more trouble with it.

 

[Stever]

Purchased my dealership showroom new 1986 2.9L Ranger STX. Within 2 weeks I found that little stumble. I purchased new plug cables, distributor cap, rotor and spark plugs because that's what the dealer's mechanic said I needed. Apparently the warranty did not cover these particular "normal wear" items after two weeks. I've had the truck looked at and the codes investigated by several other dealers. They can't figure it out.
The stumble appears at ~2500 rpm in 5th gear @ 55/60 mph. The engine has been rebuilt along with the TFI, fuel filter, gas tank, fuel pump, injectors, etc, etc...ad infintum. Change one, drive it. Change the next, drive it. Everybody, literally everybody, has a suggestion. The computer does NOT throw a code. The only thing that I haven't changed is the original distributor body, transmission and rear axle. So far, I have NOT found the cause of the stumble. The truck is very dependable, but it has that stumble.

I have been to the Tech Library and found the write up(s) on the TFI. A quick look over, suggested by the write up, has revealed an exposed wire just like it is shown in the Tech Article. My next attempt to cure this will be to unplug every connector and search for corrosion or lose fit up. The TFI will be moved to a cooler position in the engine bay and a heat sink will be installed. All grounding (earth) wires will be cleaned or replaced. If dielectric grease will slow or stop corrosion I'll do that also.

 

[scarface]

stumble

i had a similar problem

it was a tiny piece of metal that had broken off inside the alternator
that was floating around

it would randomly and intermittently cause a short which was causing a misfire

ford couldn't figure it out $$$$$ after changing every filter sensor etc....

We unplugged the alternator and it ran fine

simple fix after that

My freight liner mechanic buddy specializes in electrical trouble shooting
so i have to give him credit for figuring this out

 

[Stever]

I can only pray that it is that easy to cure this 25 year old problem. It's worth a recheck. When I get a chance I'll try it.
While checking out the under hood I decided to see about repairing the blower motor. I finally got the two screws out of the flange of the resistors. On a two wheel drive there is absolutely NO room to go through the wheel well. At least not the way I attempted it while parked on the drive. However, I found the 25 year old plastic connector to be brittle enough to disintegrate. I pulled the resistor pack out of the hole and found leaves, twigs and tiny bird feathers packed into the resistors. The resistors had gotten hot enough to blacken the leaves. A look inside the hole explained why I only have high speed blower and very little heat. The interior is packed with leaves and other debris. Clean that out, check the alternator and check every wire in the engine compartment. Sounds like a fun weekend.

 

[scarface]

stumble

nice to see someone else who bought their early ranger new off the showroom floor as well

 

[mihulka3]

Got the parts rounded up. Tomorrow new fule filter(s) and O2 sensor.
Going to reset the timing and install new PVC valve.

 

[TwoWhels]

Mine does it also...have a big collection of JY 2.9 fuel injection parts.
On the road spares.
Real sure it is my MAP sensor.
Every one I have it misses a little different when I change them.
Going to have to buy a new one someday.