NH LS170 Stalls Under Load

[TKO]

New to this forum, thanks for the assistance.
I have a LS170 with a brand-new rebuilt Shibaura N844T engine. Installed all new components, including OEM injectors, fuel return rail, turbo, filters, water pump, starter. The only original part is the fuel injection pump, but the machine ran prior to the rebuild.

Here's the issue: The machine will start and idle fine and will rev up and run all day but when moving forward at full stick or under load, it stalls out as if it's starved for fuel. The machine will run in reverse without stalling and will maintain rpms if you creep along. I have changed both fuel filters to OEM, checked all lines and injectors for leaks, checked and cleaned the fuel pickup tube, emptied the fuel tank and replaced with fresh fuel, removed the fuel cap, removed the air filters and replaced the electric fuel pump. I have also adjusted the play out of the throttle, but the machine will also stall if you cut the throttle back quickly. Sometimes you can feather the throttle and it will regain rpms without stalling. Again, it seems like the fuel is getting shut off.
Could this be injection pump timing? What am I missing? What else should I check? Any and all help appreciated.

 

[Simon C]

Have you installed a gauge to measure available pressure going into the main injection pump. Out of curiosity what made you decide to change all the parts listed as they would be a few dollars. What was the machine doing before you bought all these parts.
Simon C

 

[TKO]

Had a hole in #3 piston, reason for rebuild. Replaced injectors as a safe guard. Fuel return line was cracked and leaking. Fuel filters were replaced trying to troubleshoot this issue.

Have not measured pressure but can. What should it be?

 

[1978case]

I don't remember where NH started using the hard plastic fuel lines that have the push on ends, but we had quite a bit of trouble with them. Not leaking fuel but air ingress. Engine would have excessive smoke and misfire. I don't recall the problem being intermittent though.

 

[Simon C]

Just for your info, if you had a Camshaft sensor or Crankshaft sensor going off intermittently the engine would instantanously bog or die. Computer needs to know where the crank and cam are to know when to fuel. If no signal, no fuel. Harness could be faulty as well and would need to have those individual wires to the sensors tested each one at a time under a 2-5 amp load to prove they can take some load. I built a wire tester with a 1156 bulb with a pigtail harness and extensions added to each wire end with alligator clips on the end. I hook up the one end to battery positive and the other end to the wire I want to test.
The far end of the wire being tested goes to ground to complete the circuit. An 1156 bulb draws 2.1 Amps and there are stronger ones out there. You can wiggle the harness while the load is on to see if anything is faulty.
Some things to check before buying expensive parts.
Simon C

 

[Simon C]

Had a hole in #3 piston, reason for rebuild. Replaced injectors as a safe guard. Fuel return line was cracked and leaking. Fuel filters were replaced trying to troubleshoot this issue.

Have not measured pressure but can. What should it be?

No idea for exact pressure, need manual to know unless someone else has the info.
Simon C

 

[TKO]

Replaced electric pick-up fuel pump to ensure 8-12psi, per spec. Previous pump was 4-6psi. Machine starts easier but is still bogging on incline or if hydraulics demand power. Not sure where to go from here.

 

[Simon C]

Are there no codes, or do you need a lab top to get the codes out. Does it put some kind of lamp on when the loss of power happens. Have you with a pail vacuum sucked the bottom of the fuel tank in case something is loose and floating around down there. Almost certain it is not the problem however.
Good question, have you hooked up your gauge to watch the fuel pressure while it bogs. If the fuel pressure does not change , your problem is control circuit related to the computer. The reason I say that is that you state that it can reverse fine. The engine does not know if you are going forward or reverse as it only turns turns a pump.
The wheel speed sensors are what tell the computer which direction you are going.
Have you tried to put a load to the engine with the boom up to the top and with engine revved and hold for 5 seconds.
If it can do that your problem is control circuit. If the engine can take the heavy load that will rule out the cam and crank sensor.
You need to test your wires from the computer harness to the end of each speed sensor wire with a tool as I posted in post #5. Possibly the computer is having some problem, but need to test the harness and sensors thoroughly first.
If I have missed something let me know what.
Simon C