M816 power questions

[AMGeneral]

Ok,here's the problem.My 816 just doesn't seem to have the power it should,plus the engine seems to have much more "combustion knock" under load and emits very little if any smoke out the stack,So far this is what I have done to the truck,

Replaced all rubber suction lines from the fuel tank to the Injection pump
Rebuilt the Injection pump
checked all suction lines for air leaks from the tank to the pump
set all the valve and injector clerances

still the truck seems to have low power,I've seen other NHC powered trucks that bellow smoke like a freight train,yet mine smokes very little.

Any suggestions?

 

[red devils dude]

it is a 36,000lbs truck with 250hp, but have you re checked the fuel filters? checked the fuel pump for pressure?

 

[AMGeneral]

Fuel filter has been changed regularly(every oil change).It would help if I had driven another 800 series truck to compare it to.All I have to compare it to is my Multifuel deuce and my M52A1 Mack powered tractor.The Mack will outrun and out pull it hands down running on 5 cylinders!!Haven't checked fuel press,does the NHC have a check valve in the head /return line that keeps a regulated pressure to the injector cups?

 

[red devils dude]

I woundnt think so but I'd have to check a manual.

 

[poppop]

My M813 smokes very little and I had some questions about power on the 750 mile road trip I just made. It would strain going up hills with no load in the bed. The fuel filter was new and the old one I took out was clean as a whistle so no junk in the tank. I followed Ron's tractor wrecker for a few miles and he could pull away from me and his truck boiled smoke.

 

[73m819]

theres a little fuel filiter in the ip, check that for fuel restuction, most 800 owners dont know about it, let me check some manuals and i wiil come back with more info on it.

thanks lloyd, letting me know about the smoke and power, the 819 will do 65 all day on the freeway at 2000, but hates longggggggg steep hills

 

[poppop]

Hey Ron
It was upsetting to have you pull away from me with your heavy truck. I will try to have that fixed before we convoy again.

 

[73m819]

thats why i slowed down, thought you had broke down for a minute till saw you come around the bend, now that i have a bumper i can always push

 

[TacticalTruck]

Are you guys running stock springs and fuel buttons in your injection pumps? I picked up a purple sping and a #18 fuel button but I haven't had a chance to put them in. My M816 just keeps 53mph on the flat.
Jeff

 

[AMGeneral]

I had mine turned up a small bit when the injection pump was rebuilt.Has anyone had a problem with the injector cup seals going bad on their NHC 250?,I'm probably grasping at straws here.

 

[TacticalTruck]

So has your truck always been under powered or has it lost power since you've owned it?
Jeff

 

[AMGeneral]

Always seemed under powered/weak.Also extremely hard to start in cold weather(40 degrees or less ambient air temp) the intake heater is working properly though.

 

[TacticalTruck]

Mine was very difficult to start in the cold untill I added a block heater. As far as power, I don't know, seems like the pump needs to be turned up more. The stock primary fuel filter is prone to pull air at the o-ring.

Jeff

 

[73m819]

fuel pump

heres a pic of the 809 fuel pump used on the wreckers(will work on all), will post the other pump tomorrow, this is a take apart pic but shows the filters

 

[WillWagner]

RE: fuel pump

Don't know much about the 816, but I do know Cummins. Do easy things 1st, If it felt low on power prior to the pump rebuild, maybe it's not getting full throttle. Take the throttle linkage off, not the arm on the pump, only the rod from the pedal. Push the pump lever to full throttle and mark it. put the linkage back on and see if it's going to the mark you made. If it's not, adj. the rod, dont mess with the set screws on the pump for throttle travel. Is it an AFC pump? if so, make sure the line from the intake manifold is clear and not pinched/smashed check the fitting too, take it out, there are check fittings that look like a regular one but they won't let manifold pressure to the AFC. The filter inside the pump is only for internal pump failures, filters from the inside out and has a magnet in it. If the pump was rebuilt, they should have replaced it, FYI, never seen the screen cause a low power complaint. If it's an AFC pump, you can put air...25 PSI..to the afc and drive it to see if the power is better. That will tell you if the pump shop set it correctly. Ask the pump shop for the stand report and ask what the rail pressure was set at. Cummins gives specs like...125 to 148 PSI at a given RPM. They should have set it to the high side of the specs. Yes the problem can be injectors, no seals in the injectors, all class fit. Were the injectors loose when you set them? if so, they will be carboned inside the cup. Cummins sells injector flush. Maybe try getting some, any truck dealer..Pete. KW.IHC, Frtlnr, can get it for you, Works good. Seen it raise HP by 20 at the rear wheels with just a flus. All it does is clean the carbon from the inside of the cups. Hope this helps.

 

[AMGeneral]

Ok,checked my throttle linkage,getting full throttle,re checked all fuel line connections,tight,no leaks,fuel or air.I'm gonna try the injector flush this weekend,Is there any way to turn up the fuel without disturbing the governer settings?I do not have an AFC pump,no connection to the intake manifold.ALso found that my manifold heater was burnt out though it tested good for continuity.

 

[WillWagner]

An 855 shouldn't need an intake heater to start. If you need a starting aid or need to plug the block heater in to get it warm...when it's not below freezing outside!...it's worn out. Yes, you can up the rail pressure w/o messing with the governer. On the throttle shaft, there should be what looks like a ball pushed in there. Thats what it is! If ther is no ball, just a hole or it's flat, 1/2 the work is done. No hole, just stick a screwdriver in the hole and give it a 1/4 turn at a time, CCW 'till you have the power you feel you need, flat end, probably silicone. Remove it and do the above mentioned. A ball, use a 1/8 drill and drill it out, gently, don't let the drill hit the screw when it goes through, and do the above procedure. A word of caution...if the engine isn't piston cooled, be careful if you juice it up, you will hang a piston. This is only for a PT pump. If it is a PTG, the one with the round plate with a snap ring behind the throttle arm, this isn't how to do it. These pumps need to come apart and be shimed to raise the rail pressure.

 

[73m819]

the 809 uses a standard or a variable speed pt/afc pluged fuel pump, the varable speed is used on the 816 and the 819

 

[WillWagner]

Well, there's another thing to look at. Make sure the VS lever is staying all the way to the front or the back, depends how yours is set up. If it moves when the VS part isn't in use, it will give you VERY low power. Stand next to the engine with it running and give it full throttle, if the VS lever moves, thats your problem. What ever holds it in the "downstairs use" position has failed.

 

[73m819]

will if i sent you a full tm, a -34 in pdf could you down load and save, this tm has the blow up pics of the fuel pump and ALL the bits and peices, this mite help you look at our fuel pump problems, if i can send me your email