M920 Engine RPM retarded - Page 2 - Steel Soldiers::Military Vehicles Supersite

WillWagner · 02-11-2011, 00:04

If it only goes to 1200,
Make sure the tach is correct...sounds stupid, but I have seen that!

Make sure it is getting full travel on the THROTTLE SHAFT. Should be 37 degrees of travel. If the shaft is scored the shaft will stop and the lever will break over and make you think is going to full throttle. While you are there, make sure the lever does in fact break over.

If it's a VS type pump, make sure that the upper throttle lever is staying at the stop. If it moves when the automotive governor is in use it cuts the auto gov speed back.

Fuel restriction.

eldgenb · 02-11-2011, 02:52

Quote:

Originally Posted by WillWagner

If it only goes to 1200,
Make sure the tach is correct...sounds stupid, but I have seen that!

Make sure it is getting full travel on the THROTTLE SHAFT. Should be 37 degrees of travel. If the shaft is scored the shaft will stop and the lever will break over and make you think is going to full throttle. While you are there, make sure the lever does in fact break over.

If it's a VS type pump, make sure that the upper throttle lever is staying at the stop. If it moves when the automotive governor is in use it cuts the auto gov speed back.

Fuel restriction.

Thats a good point, when I was on my road trip home I could not get my jake to work and my engine idle kept climbing for no apparent reason, turns out that the throttle lever on the pump had loosened up a little and had the throttle open a little bit all the time and as the truck would warm up the throttle would climb. Simple fix though, send your brother in law with a crescent wrench and a flashlight in the engine compartment and tell him what to do from the street while not getting hit by cars! Oh those are the moments story's are made of.

Bearpaws · 02-11-2011, 23:48

What does the exhaust look like? Try all the easy fixes first: change fuel filter,check for air intake restriction, run truck with throttle linkage disconnected. Manually stroke the PT pump to see if you get full rpms. Should be responsive from a idle to full stroke making the engine torque the chassis a bit. If it runs good then check linkage for problems. If the engine is still sluggish then you might check the fuel line from the tank. Old hoses have started coming apart inside and blocked fuel with a flap of hose linning before in my years working on these engines. Next try running a fuel system flush. Cummins # 3885823 fuel system cleaner. Go to your parts store and have them make two hoses six feet long. One hose #10 with a 5/8" FJIC fitting one one end and one hose #8 with a 1/2" FJIC fitting one one end. Put the #10 hose on the fitting next to fuel fiter. Then put the #8 hose on the return line from the hard lines on the side of the engine block. Put both hoses in the cleaner tank opening. Make sure they are at the bottom of the tank. Start your truck and idle around 1000 RPMs. Don't leave your truck running without someone watching it because it will start climbing RPMs as it cleans. This cleans the total system bypassing your fuel tank. Run this cleaner for 20 min. or more but don't run the tank dry. Shut down then remove lines and reconnect your lines. Dump remaining cleaner into your fuel tank. Should be some junk at the bottom of the cleaner tank that came out of your system. This cured a lot of problems over the years for me when engins sat with old fuel in them. And a good practice to do prior to running the overhead on these NTC engines. If that didn't cure the problems then the tough part comes into play. Remove PT pump and injectors and have them rebuilt. Faron..

M920 · 02-12-2011, 02:47

Quote:

Originally Posted by jamboly

We also just got an M920 in for the Military Museum of Texas, and are having what might be a related problem. With engine in neutral, engine revs up just fine. However, when you put the transmission in gear, the engine doesn't rev up at all???

Jim

Ok...here is part of the problem, the CAT 7155 tranny, found in the M920, has a centrifugal clutch, NOT A TORQUE CONVERTER! Therefore you can NOT treat it like an automatic. If you have the tranny in gear, and try to rev up the engine you are forcing the clutch to slip and that could damage it or even burn it up! Unlike a torque converter in an auto tranny, you CAN NOT run it up to "stall speed" against the torque converter, in order to test the power of your engine.

Just thought, I would make you aware of that, so you don't damage your transmission.

Soni

M920 · 02-12-2011, 02:55

Oh....one other common problem, besides all the good tips above, that makes the PT not get full throttle, is the presense of the two manual trottle cables from the dash and the rear winch control, that somtimes don't let your linkage move all the way forward. You might want to check that to.

Soni

jamboly · 03-26-2011, 15:53

I think that the problem with my M920 is not that the engine does not come to speed, but that the tachometer is not working right (truck runs 65mph if speedometer is working right). The manuals I have show the truck having a mechanical tackometer (flex cable from tack to engine). However, my truck has an electronic tach. Does anybody have manuals on how to trouble shoot to tell if my problem is the tack gauge or sending unit?

Jim

PS anybody know where to get a good M870 trailer?