Skipping NHC-250, bad fuel line or overhead adjustment?

[sandcobra164]

My truck has recently developed a curious condition. It starts fine but sounds like it's only firing on 4 cylinders. After driving about 30 minutes it's fine. Idling for 30 minutes before driving does not cure the issue which in my thoughts would be air sucked in and stuck in the fuel passages in the heads. Let it sit overnight and the process starts again. I'm planning on replacing the fuel lines and fittings from tank to injection pump but I'm curious if a loose injector setting would cause this after years of no issues before I pull the valve covers. Calling out Will Wagner for advice.

 

[Elijah95]

Do you still have the original flexible fuel lines? They are known to permeate and allow air in, while not allowing the larger fuel molecules to escape. Might be a good opportunity to delete the fender mount fuel filter and upgrade to spin ons there 10 micron down to 5 micron, then dual fuel lines to supply the pump for a little better oomph on the road if you haven’t already done such

Have you replaced the o rings in your primer pump? They can shrink and do the same thing.

Definitely sounds like air getting in allowing fuel to drain back to me


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[ca1517]

I had a stuck injector on a Detroit Series 60, it did the same thing as what you are describing. I ended up filling the fuel filter with seafoam, and a again with marvel mystery oil, it finally cleared up.

 

[sandcobra164]

Corey,
I had not even thought of that but now that you suggested it, I bet that's probably what I have going on. I feel like the skip is too consistent in the firing order to be air in the system and if it were air in the system, I would think it would "bleed out" after 30 minutes of idling. I'm going to change the fuel line either way due to age but I'm interested to see if I have an injector or two stuck in the bottomed out position. I bet once running they get warm enough to loosen and start firing again. I'll post back my findings, I'm off Monday. I've not run the overhead on this truck before so I'm sure it's due.

 

[sandcobra164]

I think ca1517 had just the right advice. I've been extremely busy but found time after Church today to take a swing. Cooler weather helped as well and my truck is advertised on the Church Bulletin as participating in the Fall Festival. Anyhow, I pulled the canister from the driver's side fender and my goodness. It had nice fresh fuel at the top and brown sludge down in the bottom. I was happy that it made a noticeable suction sound as I unbolted the canister, fuel lines must be solid. Re-assembled with a new gasket and o-ring and it fired off about the same which I expected. I dosed the filter canister with about 16 oz of diesel injection cleaner and topped off with diesel from the tank. I poured the rest of the injection cleaner in the tank and hoped the test drive would provide good results. 5 minutes in, still hitting on 4 or 5 cylinders but clearing up. 10 minutes in, hitting on 5 under throttle but smooth on part throttle. 15 minutes in, we're almost there. 20 minutes in, back where we need to be. Smooth acceleration with no skipping, idle is nice again and I'm hoping that it does well from a cold start tomorrow after work. I really over thought the issue, it ran fine the last time I ran it. It sat for some time and wasn't quite right. Start with the basics and when working with diesels, that starts with clean fuel.

 

[WillWagner]

Just saw this, been out and about. Any smoke? If so, what color? Isolate the engine from the chassis. Run a line from a clean container of go juice directly to the pump and see if it cleans up. If there is enough air in the system to make it run really bad, it could take a bit for it to clean up. Sometimes starting it, throttling it up a few times, shutting it down and letting it sit will purge the air from the system. You will know when you re start it, it will fire faster. Wait a while to re start it. If it still misses, as soon as you fire it, go to the exhaust side and feel each cylinder as it warms, temps will come up gradually, outer cyls are usually a few degrees cooler and get warmer toward the center of the engine, companion cylinders should be close to the same.....1 & 6, 2 & 5, 3 & 4. If you have a non contact temp gun, use it. If you want to yack, PM me and i'll give you my number.

 

[msgjd]

three of my M809-series developed the smokeless skip recently (the 813 was missing on at least 4 cyls) after only getting run a few hours a year for the last 3 years and not run down the road. Bad me. Fuel was changed out a couple times a year. A pint of seafoam dumped down the IP feed hose and a pint in the tank(s) cleared up the issue on all of them within a day or two of intermittent running and gradual driving. Luckily, projects picked up and they are back to weekly operation with the others

 

[sandcobra164]

@msgjd,
I honestly think that's some of my trucks problem as well. It sat too much this year. I haven't used Seafoam yet but I'm not far from trying. I did put a bottle of Howe's Diesel Treat (not meaner cleaner, just regular) meant for 320 gallons on about the 50 gallons in the tank. I'm going to try driving a little more each afternoon and see if I can burn out the gunk. Mine's not completely smokeless when skipping, it has a very light haze of grey. When hitting on all 6, it has a slight black haze when standing on the throttle from idle since I turned it up a few years back.

 

[msgjd]

@msgjd,
I honestly think that's some of my trucks problem as well. It sat too much this year. I haven't used Seafoam yet but I'm not far from trying. I did put a bottle of Howe's Diesel Treat .....

Will's post above is as always, spot-on about these engines. I have learned more than a few things from his posts. Been behind 855's of all sizes for over 40 years but never had to tinker with them to keep them running until the last few years. And I know I haven't seen it all yet when it comes to cummins and I have about 9 of them here, from NTC-230's on up to a 400. So please don't take my simple fix to be the gospel. I was only lucky I didn't have to give Will a shout

What I mean about smokeless is there is no smoke produced from the skipping cylinders while being cranked. I'm new to using seafoam but have heard about it for some time now. They make a few different products, at least two have almost-identical cans and markings. I used the one labeled "Motor Treatment." It of course isn't a cure-all for all situations but it seems to have done the trick for three particular ladies who were apparently letting me know they were really angry for lack of attention !

 

[frank8003]

One can just make their own seafoam or buy the commercial product or just go to HD and get a can of naphtha and put it in the tank. Problem is ULS diesel fuel being sold as diesel is not enough for old trucks.

 

[msgjd]

...Problem is ULS diesel fuel being sold as diesel is not enough for old trucks.

yup, it's crap fuel .. i regularly add lube to the fuel when the trucks are working .. the three i had trouble with were expected to work but it didn't happen thus they didn't get the lube .. even the fuel oil we use in the off-road equip isn't what it used to be , still having trouble freeing up the rack on a D53A dozer that sat a couple years .. fortunately i have an easy source for non-ethanol for my oldest trucks and equip, thus no longer any trouble with the gas stuff

 

[WillWagner]

ATF meant for older vehicles, like dex/merc is very high in detergent, it can loosen things up. Seafoam, I think, is a water based additive. Seen it used on gas engines, it is kinda like when a l o n g time ago we used to pour water down the carb to remove carbon. I haven't had any ULSD go "bad" like the gas does. I just put 15 gallons in my 06 duramax that I had stored for 5 years. Runs fine. The only "bad" diesel that I have had was from a local station whose prices are .50 per gallon or more, less than the normal stations. That stuff killed 2 sets of injectors that I know of, I stopped using it when after putting 10 gallons in, the engine surged at idle, smoked, had low power and smelled terrible, the exhaust smelled like when an old gas engine "diesels" when it is shut off. I think it is bio diesel, not ULSD.

 

[sandcobra164]

Truck is cured after changing the fuel filter, cleaning the crud out of the canister, dosing up heavy on some Howe's lubricator fuel treatment (all 32 oz to about 50 gallons so about a 7 times over recommended treatment) and a heavy right foot on some long drives. A side effect is I found out my intermediate exhaust pipe broke at the joint where it attaches to the muffler. I guess I hadn't driven the truck without earplugs for quite some time. I found a good take off locally and already had a new muffler from the last GA Rally. I honestly can't believe how quiet the truck is now and am so happy it's running well. Best advice I can give after this experience is run them often, drain the water out of your fuel canister regularly and as always, start with the small stuff when diagnosing a problem.