Bucking on Deceleration

[MPatty]

Bucking on deceleration: when decelerating between 2000 rpm to 1500 the truck will start to buck. It seems very similar to a u-joint, but all three rear u joints have recently been replaced and are tight. Accelerating through the range it is not noticed and deceleration in any other RPM range it doesn't do it. The gear doesn't matter. Once it starts bucking I can begin to accelerate again and work it back out. The bucking immediately stops if the clutch is depressed. The speed does not matter, but it does seem less violent in higher gears. Any help on where to start looking.

The Engine was rebuilt approximately 3000 miles ago and has been doing it since then. It seems to be getting worse.

 

[BrianX128]

Rear pinion engagement maybe? Something with driveshaft and carrier bearing that doesn't like if the back of the truck lifts up some on deceleration vs being pushed down on acceleration? I'm just guessing here, that's odd for sure.

 

[ROCK HARVEY]

I wonder if you’re experiencing some axle wrap, and it’s changing the pinion angle enough to cause the u joints to bind. Any way you could jerry-rig a camera under there like this guy did to see what’s going on?

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[rhkcommander]

Does it do it while revving in neutral at all?

If not, see above. If so, you have a fueling issue.

 

[Jesus Freak]

I thought my axle was "rapping" one time, but I noticed that the beat didn't have enough bass, so I concluded that it was really "rocking and rolling". But I'd bet on the fueling issue, maybe a filter.

 

[MPatty]

Haven't been able to tell anything while revving in neutral. I do have an E-Fuel setup with a pressure regulator right before the Injection pump. With the E-fuel, air intrusion shouldn't be as much of an issue but I guess the pressure regulator could be not keeping up like its supposed to.

My bypass regulator and injector return Y into each other... wonder if that is causing back pressure on the injectors/ injection pump?

 

[Black dawg]

I have noticed this with injection pump issues or retarded timing. What is your timing set to?

 

[rhkcommander]

Haven't been able to tell anything while revving in neutral. I do have an E-Fuel setup with a pressure regulator right before the Injection pump. With the E-fuel, air intrusion shouldn't be as much of an issue but I guess the pressure regulator could be not keeping up like its supposed to.

My bypass regulator and injector return Y into each other... wonder if that is causing back pressure on the injectors/ injection pump?

We'd need more info on your setup to tell , might be better for testing to bypass temporarily to rule it out

 

[IDI-IKE]

I've seen this many times on idis always comes down to fuel pressure/flow or air in fuel feed. I would check for air, check pressure at wot, see if fuel filter needs replacement