Surging in 3rd and 4th (1 Viewer)

[crave reFleXion]

Alright... So I think I've figured some of this one out, but I thought others might be able to chip in. For a while now I've noticed that my Injector Pump (IP) can be slightly temperamental. Day to day I find that the amount of power the engine delivers fluctuates a bit. Some days I get really nice responsive power throughout the revs (up to 3500) and the engine pulls really well, and then other days it can be a bit lazy and feels sluggish. I also started noticing recently that I have less power when I switch between tanks. Finally, recently I've been getting some surging in 3rd and 4th under acceleration, which feels like the clutch slipping, but I now think it is fuel related.

The last week or so on one tank I've had more consistency with the engine and power without any of the surging; however, after filling up this morning and switching tanks the surging came back immediately in 3rd and 4th and power felt down. After work, I will switch back to the other tank to see if it goes away so I can isolate the issue to the one tank.

My thoughts are...
1) Fuel pickup / fuel lines are blocked with diesel growth
2) Fuel filters - two pre lift pump and one main before IP are potentially blocked up (although I replace these every service)
3) Fuel Lift Pump screen is blocked.
4) Air leak somewhere in the system.
5) Tank breather is blocked and creating a vacuum.
6) Some issue internally in the IP.

Any thoughts?

Has anyone experienced similar issues with their engine surging in 3rd/4th, which felt like the clutch slipping, but wasn't?

 

[roscoFJ73]

It sounds like fuel starvation. The rpms are probably lower in 3rd and 4th, but it uses more fuel due to the load on the engine.. I would set up an independent fuel supply from a 5 litre container. This should isolate it between engine and fuel tanks.
Blocked fuel pick ups can be temperamental. They block/unblock on a whim.
I cant see algea in the fuel lines being a problem if you have been driving it regularly.
If its an internal problem in the inj pump, my guess its the fuel governor

 

[crave reFleXion]

Still doing it on the way home from work... It's specifically when the revs are low in 3rd and 4th and under heavy acceleration. If I give it perhaps 3/4 throttle it accelerates fine and once I get to around 2300 revs it accelerates like normal with full throttle.

 

[roscoFJ73]

Is it a rotary or inline pump?

 

[crave reFleXion]

Rotary (14BT)

 

[crave reFleXion]

So, since last week I've only been running on the rear tank and the surging has gone away completely, which means it must be something to do with the front tank. I gave the fuel lines a quick blow out with compressed air last night and once I run the rear tank a bit lower I'll switch over and see how it goes. I'm guessing it might be a partically blocked pickup as @roscoFJ73 suggested above, but we'll see. I'll post back results later.