M936A1 Wrecker PT pump screen?

[SLOrazorsedge]

Happy Sunday all! I have a M936A1 wrecker with NHC250 motor. Long story short, one fuel tank was contaminated, pretty much overcame the frame mount filter and the PT pump and engine ingested the contamination. The motor had a severe "diesel knock" and ran very rough. I've cleaned the tanks, replaced the frame mount filter, blown the fuel lines out back towards the tanks, have clean fuel, Diesel Power injector cleaner and premium 2-stroke added. The truck still starts with the bump of the starter and largely sounds very good again. I can run the RPMs up from idle to 2100. There is a bog down from about 900-1300 RPM. Took it for a drive and it is anemic on power. Once it shifts to 3rd, forget it. TM's talk about cleaning the PT pump screen. No problem finding said screen on my M923A1 pump, its located on top under a hex bolt. The M936/M936A1 trucks use a different PT pump, They have a VS governor for the auto throttle during crane use, PN#3045424-9254, NSN#2910-01-218-5158. Both myself and another SS member have searched hi and low and are unable to locate the PT pump screen on our wreckers. Either the PT pump is delivering inadequate fuel delivery to the injectors i.e. plugged screen or what? Anyone here advise on where the PT pump screen is found on the wrecker pumps? Any advice on the loss of power? Thanks for any input.

 

[Swamp Donkey]

Look on the bottom of the pump.

 

[SLOrazorsedge]

I'll look again but we didn't find one during our search. Maybe its flush and painted over? Thanks for the diagram :0)

 

[Floridianson]

That screen is on top and that pic should be flipped to be correct. Looks like a large flat head screw. Clean real well before you unscrew it and light oil on the threads before install. Just go slow and don't get it cross threaded an you will have no problem.

 

[M35A2-AZ]

His pump is like my pump on my M936, it does not have a screen on the top. Now my M923A1 has one but mot the M936.
It is due to the auto up on the wreckers not having the same type of pumps.

 

[SLOrazorsedge]

Thanks to Swamp Donkey, both M35A2-AZ and I located 2 possibilities on the bottom of our pumps. Mine has a small diameter flush mount hex plug on the very bottom of the pump. Further back and upwards there is a machined recess with what looks like a 7/16" hex bolt. That would seem to be the logical IP screen location as the hex plug seems too small in diameter to accommodate a screen. The hex plug is located where the diagram depicts that Swamp Donkey posted. As work permits, I'll r/r each plug and advise what I find.

 

[Scar59]

Subscrided for later, good info.

 

[Swamp Donkey]

Adding the TM and Work Package numbers, along with the NSNs, per request.

 

[SLOrazorsedge]

Update, neither M35A2-AZ or I could find an IP filter screen in our NHC250 VS wrecker IP's. After cleaning my fuel tank, changing the large driver side fuel filter, the hard diesel knock resolved itself. The motor starts immediately but has a lag on run up. The original fuel filter can was badly rusted at the bottom drain area inside the can. I just replaced the entire filter unit with an updated unit that has a Schrader valve on the center bolt. Changing out the unit was straight forward with the new unit. We discovered something cool re purging air from the unit. I broke lose the fuel line from the IP and using a small funnel, poured fuel down the fuel line which filled the filter can. Once fuel stopped flowing and the funnel remained full, we purged air from the filter via the Schrader valve by depressing the valve stem. Did that 3-4 times until fuel purged from the Schrader valve. Leaving the fuel line full, I reconnected it to the IP. One pump on the IP hand pump verified the system was purged of air and fuel purged out the bottom of the hand pump valve. Closed off the bleeder screw, secured the hand pump handle. I then flipped the ignition switch on waited for the anti-lock brake solenoid to cycle 2x and bumped the starter. Instant motor start resulted without any burps, stalls or bogs! We're back in business again. Would still love to locate the mysterious IP fuel filter called for in the TM's....

 

[M35A2-AZ]

Glad you got her going!!!