Diesel Mechanics advice please

[diverman555]

I have a M923A1 is it a 1986, NHC250. When I got it a couple months ago, the first thing I did was drain the fuel tank, reached in and dried it as much as possible and let it set open for the day, then added lucas fuel additive for diesels and put in 25 gallons of fuel. I changed all the filters, removed the fuel hand pump and replaced the o ring so it had a good seat. After all fluids and filters were changed and fresh fuel was put in I started her up. After hand pumping fuel up I fired her off. The first time she cranked for maybe 8 seconds and fired and stayed running. I checked the gauges and oil pressure was good. After putting about 75 miles on her with no issues, I stopped at a light and when I pushed down on the fuel pedal she acted like she was down a cylinder and was pulling very slow and building power and RPM
very slowly. I let off and on a few times and she started pulling again normal.
This has happened a few times now. It's just like she is down a cylinder. Do you think a injector might be bad. The truck has about a hundred miles on it since all filters and fluids have been changed. Ideas of what to do or is there a way to check for a bad injector that is not always bad? you ideas of what it could be?

 

[maxxplanck]

It was a good idea to drain the tank but what you should have done ( and I do this with all my GL trucks ) is dropped the tank and power wash it then let it dry for a week. Then I add Sea Foam and new filters. Most of these trucks have about 25 years of rust and stuff in the bottom of the tanks.

 

[WillWagner]

800 series 5 tons are known fir having junk fuel lines that cause air in the fuel, maybe the 900 series have the same issue? I'd start by looking at the lines and switching valve/tee for the suction line.

 

[diverman555]

The fuel tank is aluminum and no rust at all

 

[goatijoe]

If you think its an injector take a IR. temp. gun and shoot the base of the manifolds at the flanges and see if any of the ones are way cooler or hotter than the other ones.

 

[indy4x4fab]

Hay diverman give me a call real quick 317 522 6608, I have a 250 that is down a cyclender right now and we can compare notes to see if its an injector problem or not.

 

[overlordofmars]

I would go with a weak or dripping injector. you should remove them and go to the local big rig shop and have them tested. I have had used engines that ran fine when pulled get bad injectors when they sat for over a year. I also had a freak chunk of junk filled injector line start throwing chunks of sludge into the injectors after I used injector cleaner.

 

[appnut1]

You should able to remove the valve covers and with the engine at an idle compress the injector plunger with a LARGE screwdriver thus cancelling the cylinder, the bad injector/cylnder will not cause a drop in the RPM when it is cancelled.. Using this method you should be able to isolate the injector/cylinder that is giving you trouble.

 

[Hammer]

Fastest way to test a cylinder, get a spray bottle with water in it. Spray each exhaust runner, then start the engine. Fast way to see how the water evaps. Number 1 and 6 take a little longer to evap the water.

I would not rest until you have replace ALL rubber fuel lines. A little air leak can feel like this as well.
I personally changed everything from the IP to the tank, including converting to a spin on fuel filter. Made my life SO much easier and so much more hassle free of the NH250 issues.

 

[Csm Davis]

800 series 5 tons are known fir having junk fuel lines that cause air in the fuel, maybe the 900 series have the same issue? I'd start by looking at the lines and switching valve/tee for the suction line.

Same system on the 939 basic and a1 as on 809 series

The fuel tank is aluminum and no rust at all

Tank is stainless steel, fuel cap is bronze, strainer may be aluminum or steel.

I would definitely check and or replace all the rubber and plastic fuel lines.

 

[diverman555]

Thanks guys

 

[WillWagner]

Start with easy things first.

 

[nk14zp]

I'd check the filters again.

 

[crazywelder72]

You should able to remove the valve covers and with the engine at an idle compress the injector plunger with a LARGE screwdriver thus cancelling the cylinder, the bad injector/cylnder will not cause a drop in the RPM when it is cancelled.. Using this method you should be able to isolate the injector/cylinder that is giving you trouble.

Will this work on a deuce also? I don't have a IR temp gun but i did like the idea of misting the water on the exhaust manifold and watch for evap.