I am new to the forum and new to diesel engines. My problem is that when I am getting up to speed everything is smooth until I reach about 45mph and the transmission shifts into overdrive the engine starts bucking or feels like it's cutting out. When I accelerate it gets smooth again. It seems to buck when running 45 - 60 mph in overdrive no matter the conditions.

Doesn't matter if motor is warm or cold.

Not pulling anything.

Tested FICM, all is 48.5v
cleaned EGR Valve

Truck has no engine mods, have 6in. suspension lift

 

Does your speedometer bounce around when this happens? If so it will sometimes be the Speed sensor which is located on the rear axle housing. Take it out and clean it off. It is magnetic and the tiny metal shavings will interfer with it.
I had a similar problem with my truck doing as you explained. But my speedometer also was mesed up. Replaced the speedsensor since it was bad. Also if your truck has ever had the cab off for any repair. There is clip connections at the fuse box on driverside fenderwall. I had 2 clips come loose. Found this out the hard way after speedometer and tach quit and truck was doing the bucking.

Another thing it could be is your egr valve is clogged. You can clean it off and reinstall but use new Orings on it. If none of the above the vanes in the turbo could be stuck or the turbo needs cleaned.

I know all of these could cause it to buck. Test everything out. clean your EGR and Speedsensor. Check the fuse box connections.

 

The speedometer and tach work fine. I can see a little miss on idle as well. Cleaned egr today but no change. Don't know if cab has been off. I'll try to clean turbo. One thing I noticed was the piece on front of air filter missing, wonder if that can cause problem. Also, while cleaning EGR valve, I noticed the lower o ring was messed up a little. Didn't have any replacements so put it back like it was. Will fix that soon.

 

The slightest crack on those Orings will mess that EGR up. I cleaned mine one time and didnt replace the orings. Didnt fix nothing till I got new ones on. As for the Airfilter missing something. Is it the air filter itself or to the case? I know there is a mod you can do to the case which will supply more air to the filter.

 

I can see the front paper honey comb of the air filter all the time.

 

Sticking injectors.

How often do you change oil? Why type of oil do you use? What oil filter do you use?

Buy some Rev-X oil additive, I'd almost guarantee your issues disappear.

 

I just got the truck and haven't changed oil just yet. Will do that soon. haven't decided what oil and filter to put in yet. I just find it wierd that injector would stick everytime i get into overdrive going 45-60mph. The truck just shakes and jerks until i accelerate, it downshifts and the shaking goes away until it shifts back into OD. I guess i don't really understand how the injectors really work. Is it possible that truck had a tuner on it before I bought it and the computer needs reset? who knows. I'll change oil and O rings on egr valve and see what happens. just seems electrical or fuel issue.

 

As far as resetting the comp goes...disconnect the batteries for a little and then re hook. Not sure this is going to make a difference though. Are you having any issues with cold starts/hot starts? The injectors on these trucks have high pressure oil pressing on the top side and thats what causes them to fire. hence the reason Mdub mentioned oil change/fuel filter change. Drain water separator? Bucking when the FICM is working correctly really points to sticking injectors and 6 or 7 cylinders firing at full bore when you press the go pedal might make it harder to feel a low fuel atomization/no fuel situation.

 

ive had a problem similar with it bucking when im just barely on the gas at like 50 mph had oil changed a few times and some fuel additive and havent seen the problem since. good luck and delete the egr! does the battery reset take off the programmer?

 

starts up fine cold/hot doesn't matter. I will change oil and fuel filter tomorrow if possible and drain water separator. This really might be issue as I noticed oil was low when i first bought it, 1/2 gallon low, filled up and no change. Hopefully not failing injector.

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also, any reccomendations on oil and filter to use, starting to get cold here in Missouri.