M817 Blowing smoke but won't start

M817 acquired from GL has been running great for several months. Cummins would start quickly and easily even with temps in 30's. Filters were all marked as having been recently changed (go Army!). When I got it I topped both fuel tanks and put in conditioner but have always run off left tank. I got cocky and decided to give right tank a try yesterday. Sure enough, a few minutes later the engine sputtered and stopped and actually backfired (didn't think a diesel could do that). Tried to restart and it continued to blow smoke out the stack but never turned over after that. Tried everything including switching back to left tank. Cranks like crazy, but never turns over and continues to blow diesel out the stack. I am not great at diagnosing diesel problems. I figured it must be fuel filter, except the stuff blowing out the stack makes it seem like fuel is getting there. Maybe old fuel? Should I flush both tanks and replace all fuel and fuel filter anyway? Appreciate your help.

Help?

Thanks,

Rebar

I would leave it on the good tank, purge the fuel lines real well with good diesel, clean out the filter canister and put in new fuel filters. See what happens.

Too late, you need to rebuild your tank selector valve. They suck air when the orings are bad. I always tell people to leave them alone until you are ready to reseal them.

iirc, you need a #25 o ring for the big one. and one that fits the shaft.

A little searching should help find the other o ring size.

I'd consider replacing the rubber lines also. They are on hose barb fittings..

Pull the step for access.

And don't forget you have a fuel primer and bleeder for a reason.

I have a question: Is it true that blowing smoke out the stack while cranking (but not turning over) means that fuel is getting to the engine? Is it an ineffective mixture of diesel and sucked air? Is it likely that the diesel has gone bad? Also, thanks, doghead for being specific in regard to the "O" ring size--very helpful.

Thanks.

Rebar

Rebar, "Cranking" and "turning over" are synonymous... lots of white smoke while cranking means you are getting fuel with air at injection. Black smoke conditions are usually experienced while the engine is running and over-fueling (un-burned fuel)...or an excessive air restriction (un-burned fuel), or with excessively advanced injection timing (again, un-burned fuel), the NHC 250 fuel timing is fixed/set by the camshaft. Back-firing would occur if there is an un-burned fuel air charge in the combustion chamber at the beginning of the exhaust stroke. And you are right, not a normal occurrence in a diesel engine. I would take a close look at your fuel in the suspect tank...pull a sample from the bottom with a clear glass, check the odor and see if there is any water in the bottom of the tank. If you pulled a slug of water and blew an injector tip...well, never mind, you probably just have air in your fuel.
Regards, Bob

To me cranking and turning over are the same thing. Firing or coughing or popping would be trying to start followed by actually running. Just so we are all talking the same language.

Sorry about the wrong choice of words. By "cranking" I meant the starter turning the engine--all starter contribution, no engine contribution. By "turning over" I meant the engine is now contributing. It blows smoke while the starter is turning the engine--the engine never contributes. Anyway, I plan on draining both tanks, refueling with fresh diesel and conditioner, rebuilding the tank selector, and repriming. I love the availability of the fuel primer. This is my first 250 Cummins--where is the best place to bleed the fuel lines? I looked at the TM diagrams--seems like there are a lot of potential places.

Appreciate all of your help in formulating a plan.

Rebar

It likely isn't your problem...
But check it (since I had a similar problem once and this was the fix...).

Make sure that the mechanical shut down on the injector pump is completely released. I had a truck once that huffed and never started. After going through the fuel system, I noticed that the mechanical shutdown (the emergency stop lever) was slightly rotated (as if somebody had started to pull the handle in the cab and then pushed it back in), it was just enough to keep it from fully fueling... Twist the lever with your finger to make sure that the fuel is fully "on" and try it.

You've likely got air and/or some nasty fuel but it never hurts to check...

Good luck,

Most of the time "bad" fuel in a diesel is dirty fuel. Diesels will run on 20 year old fuel if it is clean. I would pressize the fuel lines from the line that connects to the IP all the way to both tank to flush any crap, change filters, and flush both tanks if they visually look dirty with fuel drained. If the bottom of the tanks are rusty you'll just keep getting clogged filters.

If you are going to rebuild the selector vavle replace the hoses and make sure the fitting are all good.

I had one that I replaced all the lines on. She'd start right up when the temp was 70 degree's or above. Below that, slow cranking, white smoke and then like a grenade going off, she'd fire up and rattle like a tin can full of marbles. The same rattle you'll hear from a NHC 250 under a load if you stomp the pedal. I always considered the slow starting thing normal until I had a M923 out here with the same motor. That truck was rebuilt in RRAD out in Texas. It had about 3,000 miles and probably very low hours on the motor. It would start almost as quick as a Deuce. The M923 gets the "free pass" on the tank selector valve but I tried bypassing that on this M818 and got the same results. The M818 had about 46,000 miles on it but it had great compression and made a 400 mile ride to it's new home without issue. It was fine once warmed up but it was a pain to start when cold.

doghead said:

Too late, you need to rebuild your tank selector valve. They suck air when the orings are bad. I always tell people to leave them alone until you are ready to reseal them.

iirc, you need a #25 o ring for the big one. and one that fits the shaft.

A little searching should help find the other o ring size.

I'd consider replacing the rubber lines also. They are on hose barb fittings..

Pull the step for access.

Click to expand...

Good call Doghead. I had the same problem.

Got back to the farm this past weekend. Sure enough, the emergency shut off valve was nudged just a little bit. So, I turned it counter-clockwise all the way, used the primer to bleed the fuel lines, left the valve tank selector on the good tank, put the pedal to the metal and that wonderful old engine just sprang back to life. Nothing quite like the sound of that 14-liter engine starting up again. Drove it miles afterward and it has tons of power and operated flawlessly.

You guys are the best! Thank you all for being so willing to help.

Rebar

Rebar said:

... Sure enough, the emergency shut off valve was nudged just a little bit. ... Drove it miles afterward and it has tons of power and operated flawlessly...
Rebar

Click to expand...

Glad to hear that you got it solved and that it was an easy fix!

CGarbee said:

Make sure that the mechanical shut down on the injector pump is completely released

Click to expand...

Where is this lever?

On top of the injector pump. The emergency shutoff cable pulls it back, but it must be reset manually(forward).

doghead said:

On top of the injector pump. The emergency shutoff cable pulls it back, but it must be reset manually(forward).

Click to expand...

I may be wrong but I believe that the -10 talks about a manual reset for the emergency shut down and WHERE to find it..