M809 series truck slow to return to idle

[1958 M274]

Well, I changed all of the fuel hoses at the selector valve, as well as the supply and return hoses at the engine. They all appeared to have been replaced at some point in the not too distant past and really didn't look bad. I also changed the fuel filter.

No change. It still starts good, accelerates quickly, has plenty of power, and takes four to five seconds to return to a 600 RPM idle after running the engine up to 2100 RPM no load and letting off the throttle.

For those of you just starting to read this, I have also checked the throttle linkage, hand throttles, and cold start/fuel primer system.

I'm beginning to wonder about the fuel pump. Has anyone rebuilt their PT pump? Does anyone have a recommendation on someone to check with on buying a rebuild kit?

Thanks!
Joe

 

[R Racing]

Maybe "O" rings in pump.

 

[bevanet]

I'm interested in how much work it is to rebuild the pump..

 

[crasheej]

I rebuilt a spare pump and the one on my 816. I believe that one of the TMs has all the info in. Can't remember which one. There isn't that much to it if you can read and understand what you read. But I believe there are lot's of pictures.

 

[jdgreen]

i got a PT pump and govenor i would like to have rebuilt.

 

[m816Buch]

my m816 did this same thing.......throttle shaft in pump was binding up, kind of scary when you take off and let off the pedal to slow down and you keep going.........i took my pump apart and rebuilt it, works great now..........my wrecker doesn't get driven that much so all the works got gummed up............will start and run it every week now

 

[Armada]

Well, I changed all of the fuel hoses at the selector valve, as well as the supply and return hoses at the engine. They all appeared to have been replaced at some point in the not too distant past and really didn't look bad. I also changed the fuel filter.

No change. It still starts good, accelerates quickly, has plenty of power, and takes four to five seconds to return to a 600 RPM idle after running the engine up to 2100 RPM no load and letting off the throttle.

For those of you just starting to read this, I have also checked the throttle linkage, hand throttles, and cold start/fuel primer system.

Joe, did you ever find out what was causing the problem?

 

[1958 M274]

Joe, did you ever find out what was causing the problem?

No, I have not had a chance to look at the fuel pump. I think I know where I can get a good take off PT pump, but it will be a few months before I'm able to get it off of the parts engine.
Joe

 

[jasonjc]

Be for you pull the pump or any thing BIG pull out the fuel pick up tubes and check them for rust and pin holes.

 

[1958 M274]

Many thanks to Will Wagner! My fuel problems with this truck have been solved!

I started off by changing the fuel filter, all of the fuel hoses, checking and lubing the throttle linkage and hand throttles, checking for a restricted fuel return line, and checking for leaking fuel at the fuel nozzle for the cold start system in the intake manifold. No change in my excessive smoke or slow return to idle. I then sent Will a message and he agreed to talk with me on the phone.

I ended up having two fuel problems.

The excessive smoke was caused by all of the injectors being way too loose. Some of them were only torqued in the 12-24 inch pounds range, which is far from being closed (spec is 72 inch pounds). I adjusted the top end (injectors and valves) as Will describes in this thread:

http://www.steelsoldiers.com/5-ton-up/73256-nhc250-valve-injector-overhead-adjusting.html

If anyone needs to set the top end on their NHC-250, I highly recommend following his instructions. Much easier to follow than the manual.

Will also described to me how to pull the plungers out of the injectors, and clean off the excessive carbon buildup that resulted from being run loose.

The top end adjustment and injector cleaning cleared up the smoke! The truck sounds great running, and only smokes a little at idle when cold. Once it's warmed up, it runs very clean. Still no change with the slow return to idle though.

Another call to Will and he explained how the fuel pump works and about a couple of adjustments. I adjusted the idle stop on the throttle shaft, which controls "fuel bleed off". This solved my slow return to idle problem. It also slightly lowered my idle speed, so I need take the plug out of the back of the pump and turn in up a couple clicks tomorrow.

A little more maintenance and I think I'll be ready for the 635 mile road trip next week!

 

[Capt.Marion]

This thread needs more video!


[sorry, I had to post it]

 

[doghead]

Another call to Will and he explained how the fuel pump works and about a couple of adjustments. I adjusted the idle stop on the throttle shaft, which controls "fuel bleed off". This solved my slow return to idle problem. It also slightly lowered my idle speed, so I need take the plug out of the back of the pump and turn in up a couple clicks tomorrow.

Could you give more detail on this adjustment when you have time, please?