M923A2 Hill Climb/Accelerate Issue

[scrump]

Hello fellow MV'ers,
I've recently changed out my fuel injection pump (that fixed my starting issues) but my truck will not accelerate very well in forward gears. I tried to climb a relatively small hill and the RPM never gets above 1000 or so. She just bogs down and then essentially stops, while the engine runs at 1000 RPM.
In reverse, it climbs the hill completely normally, which tells me I must not have an air leak in the fuel system or such, that it must be a transmission issue...thoughts?
Thanks!
Scrump

 

[sandcobra164]

My first thought is you still have a fuel delivery / injection issue. Reverse has a very low ratio which is masking the performance issue of the engine. I have a truck powered by the older NHC-250 which is known to be more robust in power at low rpm's thanks to it's huge displacement but your 8.3 powered truck should absolutely go up a small hill in forward. There are a few threads about bumping the power on an 8.3 powered truck but it requires a special tool. I doubt the shop that rebuilt the pump set it too low for the application, the truck had starting issues in the past so I'm still inclined to think the issue is between the pump inlet and tank. Have you read around here about the fuel elbow and suction tube at the tank having an issue? I'd start there and replace every piece of rubber line between the injection pump and the tank. Trust BUT Verify. Suction lines can suck air but show no visible fuel leaks.

 

[WillWagner]

Do the checks for low power....FSOV pulling in the proper distance, throttle lever to the full throttle stop, the AFC line in tact and connected, no open holes to atmosphere in the charged air, the turbo actually spinning, then pressures and restriction.

Did you have your pump repaired or get one from the interwebs? They aint all the same.

 

[Ue413]

Sometimes the symptoms aren't what you think....case in point, I was using my excavator every weekend with no problems. One weekend, I have low power. I'm thinking fuel issue all the way. After a lot of work on fuel side with no changes, I go to the air intake, and found a mouse had built a huge nest within an air intake tube and I was restricting oxygen.

 

[WillWagner]

Sometimes the symptoms aren't what you think....case in point, I was using my excavator every weekend with no problems. One weekend, I have low power. I'm thinking fuel issue all the way. After a lot of work on fuel side with no changes, I go to the air intake, and found a mouse had built a huge nest within an air intake tube and I was restricting oxygen.

Simple checks first, 75% of good trouble shooting is easy stuff.

 

[Jbulach]

Hello fellow MV'ers,
I've recently changed out my fuel injection pump (that fixed my starting issues) but my truck will not accelerate very well in forward gears...

Have you checked you fuel pressure, or installed a “new” overflow valve with your IP change? Dont think it’s a transmission problem causing starting or low power issues...

 

[74M35A2]

Install a clear piece of tube on your fuel return line, look for air bubbles. When using push button thumb primer, you should hear the overflow valve "squeak" as it unseats and allows fuel to flow past itself. This valve is the return line banjo fitting bolt. It is hollow with a spring loaded ball and seat within it. Unofficially, you can pinch the return line closed with Channel-Locks for 30 seconds or so, and then release it. This is an emergency in-field attempt to clean it if the ball is dislodged not allowing and fuel pressure to be built up within the injection pump from the lift pump.

 

[WillWagner]

Simple stuff before you go interrupting fuel systems, It takes a bit to make things run right after opening lines and such.