Vehicle Bucking in a particular RPM range.

[Madrugador]

I have a 6.2L Turbo Diesel installed in a Land Rover Defender 90 with a manual transmission. The vehicle performs beautifully at every RPM range except between the RPM range of 1600 - 1900. The vehicle starts to buck as though it is getting intermittent fuel. A fuel gauge was installed so that the fuel can be monitored during the bucking, to see if there was a problem with the pump, but upon testing the fuel stayed steady through out the bucking range, so the only thing that I can attribute this phenomenon to is a problem with the cable or the gearing. This bucking happens with all the gears in that RPM range. If anyone have any insights to this situation, please post it. Thanks for your time!
-Madrugador

[DmaxMaverick]

If fuel supply is positive and steady, that leaves the fuel injection components and the valve train. You can check the valve train deflection. Remove the oil fill pipe and observe the IP gear while rocking the crank (socket/breaker on the crank balancer bolt - it's easier with glow plugs removed). Excessive deflection indicates worn valve train components (chain stretch, etc.). The valve train / cam chain drives the injection pump. Other than that, being specific to a narrow RPM range, it's likely an issue with the injection pump (due for overhaul).

[Madrugador]

Thanks DmaxMaverick for your responds and I am going to get on it as soon as I can. I will be gone for a month or so, so when I get back, I am going to investigate these possibilities. I will get back to you with a report. Thanks Again for the input!
-Madrugador

[More Power]

EGR malfunction has produced symptoms like this too - unless your engine is running without EGR...

[Madrugador]

Thanks More Power for the suggestion. I don’t think I have a EGR, but can you explain where do I look for one. Hopefully, this is easy to replace as oppose to the injection pump. Thanks Again!
-Madrugador

[More Power]

The non-turbo 6.2L EGR valve is located in the center of the intake manifold, clearly visible once the air cleaner has been removed. Though.. with a turbo 6.2L it can be a little different.