Truck "bucks" at slow, steady speeds

[FX4Offroad]

2019 Ranger Lariat FX4
51,000 miles (Update 4/20/22 52,500 miles)
100% mechanically stock
93 octane gas only

So, first of all, except for this issue, the truck runs great. I run 70+ highway speeds and not a blip at all - ever. I consistently get 20-23 mpg mixed driving. Love the FX4 shocks and the damper.

The issue is when I run slow, constant speeds - between 25 - 30 mph. The truck bucks. It feels like it's skipping. VERY noticeable. Of course, it doesn't do it all the time - but most of the time. As soon as I accelerate - either a little or a lot, it stops the bucking and runs great. It only happens at a constant speed around 25-30 mph. The truck is 100% up to operating temperature so it's not a cold engine thing. I did have the TSB when new (~10K miles?) for the cold engine thing. It resolved that back then.

Ran it in Drive and Sport and it doesn't seem to matter, still bucks. This leads be to believe its not the transmission however, I'm NOT a mechanic so I certainly could be wrong.

Took it to the dealer and they couldn't replicate it - surprise.

Before I take the time off of work and drive it with the tech in the truck, has anyone experienced this?

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[FX4Offroad]

Because it runs perfect 99% of the time, and only experiences the issue under the specific conditions I describe, I wonder if it'll pick up any codes.

I'll pursue that suggestion. Appreciate the advice.

 

[P. A. Schilke]

Because it runs perfect 99% of the time, and only experiences the issue under the specific conditions I describe, I wonder if it'll pick up any codes.

I'll pursue that suggestion. Appreciate the advice.

Hi Jim,

I would have the dealer run a test on your injectors. Coil usually does not malfunction in a specific speed range. Just sounds like a fuel feed problem...hopefully there is a code to help diagnostics...

Good Luck!

Best,
Phil

 

[Vitis805]

Add more grease to the driveshaft slip joint splines, and if that doesn't help I reckon it's just the nature of the beefy straight-cut gears. The transmission is over built for the amount of HP and torque our stock motors put through it.

 

[rausa64]

Could the transmission be hunting for the "right" gear? Seems like my truck wants to go to the highest possible gear all the time for better fuel economy.

 

[NotBudule]

Could the transmission be hunting for the "right" gear? Seems like my truck wants to go to the highest possible gear all the time for better fuel economy.

Op said it does it in sport and tow , most likely eliminating the tranny...

 

[RedlandRanger]

At 51k, could it be your plugs are showing signs of age? I've heard others replaced them at 50k.

 

[P. A. Schilke]

At 51k, could it be your plugs are showing signs of age? I've heard others replaced them at 50k.

Hi Rob,

Owner's manual indicates to replace at 100,000 miles... which means the Durability Test trucks ran the plugs for 100,000 miles.... Puzzling why they would have not found a problem with the plugs before 100K miles..... Plugs are cheap so maybe give it a shot...

Best,
Phil

 

[dtech]

Try putting 87 octane in it . It is rare but occasionally the map sensor needs cleaning

 

[RedlandRanger]

Hi Rob,

Owner's manual indicates to replace at 100,000 miles... which means the Durability Test trucks ran the plugs for 100,000 miles.... Puzzling why they would have not found a problem with the plugs before 100K miles..... Plugs are cheap so maybe give it a shot...

Best,
Phil

That was kind of my thought process - it is easy to do and pretty cheap, so why not give it a whirl?

I've seen lots of weird stuff with plugs that magically goes away with new plugs, but that is on older engines - with that said, it doesn't' seem like replacing them at 50k is throwing money away.

 

[Toytec]

I betting on some moisture on one of the coil packs. Good time to do a visual on the plugs.
Back in the day this kind of concern I'd be blaming the EGR valve or carbon issue.
If it were me I'd be fogging the induction system with the BG or Valvoline products the Ford guys are using. But that's just me.

 

[FunInTheSun]

2019 Ranger Lariat FX4
51,000 miles
100% mechanically stock
93 octane gas only

So, first of all, except for this issue, the truck runs great. I run 70+ highway speeds and not a blip at all - ever. I consistently get 20-23 mpg mixed driving. Love the FX4 shocks and the damper.

The issue is when I run slow, constant speeds - between 25 - 30 mph. The truck bucks. It feels like it's skipping. VERY noticeable. Of course, it doesn't do it all the time - but most of the time. As soon as I accelerate - either a little or a lot, it stops the bucking and runs great. It only happens at a constant speed around 25-30 mph. The truck is 100% up to operating temperature so it's not a cold engine thing. I did have the TSB when new (~10K miles?) for the cold engine thing. It resolved that back then.

Ran it in Drive and Sport and it doesn't seem to matter, still bucks. This leads be to believe its not the transmission however, I'm NOT a mechanic so I certainly could be wrong.

Took it to the dealer and they couldn't replicate it - surprise.

Before I take the time off of work and drive it with the tech in the truck, has anyone experienced this?

I have something similar, but worse. My idle is VERY uneven. Hunts from just under 1000, to 500 or so. Only at idle, or very light loads, like 20-30 mph, not accelerating or decelerating. Maybe one cycle per second, and it's not consistent. Occasionally stalls the motor when it drops too low. Dealer has looked at it twice, without resolving anything. They had no loaners available, so I've just been putting up with the annoyance. It runs normally, except my gas mileage is low (about 14-15 mpg...). Anything but idle is ok.
I've been suspecting a problem with the PFI injectors, as they only come into play at low load and idle, and I'm about to start another round of troubleshooting with the dealer.

 

[JimJ]

That was kind of my thought process - it is easy to do and pretty cheap, so why not give it a whirl?

I've seen lots of weird stuff with plugs that magically goes away with new plugs, but that is on older engines - with that said, it doesn't' seem like replacing them at 50k is throwing money away.

I’m retired but was in the marine service business for 35 years and I’ve seen plugs go bad in 5 minutes. I’ve seen plugs fail under hard acceleration due to combustion pressure. On the ford and Chevy 6.2 I’ve seen misfires thrown and replacing the plug fixed it.

 

[NotBudule]

So , if your cruising at 25 and it starts doing it , it will just keep doing it unless you accelerate out of it ? Next time you could hit the plus on the selector and notice what gear , then see if you are shifting out of it or accelerating out of it...

 

[Big Blue]

I've been suspecting a problem with the PFI injectors, as they only come into play at low load and idle, and I'm about to start another round of troubleshooting with the dealer.

If by PFI injectors, you mean Port Fuel Injection, that's not your problem. Our 2.3's don't have them. Direct injection only.

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