The Humvee takes off on its own like if someone flipped the "After Burner" switch.

[Tiwaz]

The problem is that going at a steady speed, say…. 30 mph without changing the pressure applied on the gas pedal, all of a sudden the truck (1151) behaves like if I floored the pedal, it even downshifts on it’s own and takes off, and if I keep the same pressure on the pedal, it reaches about 50 MPH (or more) and it stays there for 10-15 seconds and then it behaves like I removed the foot from the pedal all together and it goes back to normal.
It does this even at 50 MPH the only difference is that it does not downshifts but you still hear the engine revving up and the speed increases substantially.

 

[Mogman]

I do not believe "Humvee" and "afterburner" have ever been used together before

 

[NDT]

Is there an animal curled around the injection pump?

 

[Tiwaz]

Is there an animal curled around the injection pump?

hehehe... no... the only animal present is behind the steering wheel

 

[NDT]

If you have a way of verifying that the injection pump is doing this on its own, as in the control shaft isn’t rotating, your injection pump is crapping out internally. Time for rebuilding.

 

[Mogman]

What gets me is the TPS controls the downshift, along with the programming in the TCM.
So how is the TPS creating WOT without the shaft moving and at the same time the internal gov/linkage fails do do its job creating the same WOT condition as the TPS
Or is the shaft actually moving.....

 

[Mogman]

I would inspect the linkage and cable and the accelerator pedal carefully.
Does there seem to be ANY other influence that could be a "precursor" to the event????

 

[NDT]

What gets me is the TPS controls the downshift, along with the programming in the TCM.
So how is the TPS creating WOT without the shaft moving and at the same time the internal gov/linkage fails do do its job creating the same WOT condition as the TPS
Or is the shaft actually moving.....

See this scenario is why I was halfway serious about my "animal" remark, the electronic trans won't downshift if the injection pump went to WOT on it's own internally.

 

[Thunderbirds]

Silly question, have you inspected the throttle return spring next to the TPS, the one that pushes back on the accelerator cable? Should be a double wire spring.

 

[Autonomy_Lost]

I beleive there is a switch on the accelerator pedal that is activated when the pedal goes "to the floor" and downshifts....maybe that switch is activiating early?

 

[Tiwaz]

What gets me is the TPS controls the downshift, along with the programming in the TCM.
So how is the TPS creating WOT without the shaft moving and at the same time the internal gov/linkage fails do do its job creating the same WOT condition as the TPS
Or is the shaft actually moving.....

Nothing moving.... (no strange sound.... no mechanical force change at the pedal... no clues)

 

[Tiwaz]

I would inspect the linkage and cable and the accelerator pedal carefully.
Does there seem to be ANY other influence that could be a "precursor" to the event????

Very good question Mogman but the answer is "No", I have carefully examined the "conditions" in which this problem happens and there is no consistency... no "precursor", engine temp (cold or hot) is not a factor, slope (going up hill or down hill) is not a factor (Florida is so damn flat) speed is not a factor, I don't know how to create situations that are unique but maybe I'll try to drive in D instead of overdrive and see if that changes anything .

 

[Tiwaz]

See this scenario is why I was halfway serious about my "animal" remark, the electronic trans won't downshift if the injection pump went to WOT on it's own internally.

I visually inspected the engine compartment and the pedals area but did not see anything out of the ordinary

 

[Tiwaz]

Silly question, have you inspected the throttle return spring next to the TPS, the one that pushes back on the accelerator cable? Should be a double wire spring.View attachment 935149

Hey Thunderbirds thanks a lot for the picture, it really helps A LOT to identify components in the engine compartment especially when you are not familiar with the name and location of engine components. I'll definitely be checking on that as soon as I get back to my Humvee. Thanks again

 

[Tiwaz]

I beleive there is a switch on the accelerator pedal that is activated when the pedal goes "to the floor" and downshifts....maybe that switch is activiating early?

I didn't know about this switch but definitely worth taking a look at it because it would make sense that if that switch has an intermittent contact, it would provoke that reaction. Can you tell me more specifically where that switch is located....?

 

[Mogman]

I bele

I didn't know about this switch but definitely worth taking a look at it because it would make sense that if that switch has an intermittent contact, it would provoke that reaction. Can you tell me more specifically where that switch is located....?

I think the switch he talks about is only on the 3 speed, the TPS controls all throttle functions to the transmission.

 

[REF]

Could the torque converter be unlocking causing the engine to rev up / feels like a downshift ? Possible adj or replace the switch on the brake ?

 

[Thunderbirds]

Could the torque converter be unlocking causing the engine to rev up / feels like a downshift ? Possible adj or replace the switch on the brake ?

.
It could be, but the OP also reports sudden speed increase, that wouldn't happen if it merely unlocks the TCC, IMO

 

[MarkM]

Afterburner? Yeah no that does not go into and sentence that includes HMMWV. Like slamming me into the seat. Or the houses around me got blurred.

 

[canadacountry]

@MarkM maybe you'll like to try an ex-jet engine and see what it does (if it doesn't dry up your tiny fuel tank too quickly first) but..who knows!