Cummins rough idle

[cbvet]

The Cummins in my M813 is idling rough after sitting a month.
What would you check first?
Other likely causes?

 

[NSCoyote]

fuel quality, filter condition, possible air leak in fuel system

 

[Scrounger]

The first thing to check is if there is any water in the fuel. Open the vent and the drain on the fuel filter/ water separator and see what it looks like. Don’t be afraid to drain a quart or two out. Then after closing up the drain and vent open the bleeder by the intake tube and re-prime the system. See if that clears it up. If there was a lot of water in the housing change the filter, then re-prime. If that doesn’t work look at the fuel lines from the tank to the filter housing next.

 

[cbvet]

Thanks for the tips guys. I'll check it out in the AM.
I remember now that when I had it out a month ago, I didn't drain anything when I got home. We were having a major storm, & I just parked it.
It was left sitting until I could get a muffler.
Got the muffler on last night. Then found one bolt loose & one missing from the power steering pump mount! Pump was wobbling.
Thanks again. I'll let you know what I find.

 

[cbvet]

Worked on it today.
No evidence of water in the fuel. Took out filter. It only has about 200 miles on it and looks fine.
Couldn't get it primed using the hand pump, so I took the filter back off & completely filled the canister with fuel. Messy.
Still took a long time to start, and still a little rough at idle. Runs great on the road.
If it had a gas engine I'd be adjusting the idle/mixture screw.
I added a lot of Diesel Kleen to the tank to see if it would help.
I'm wondering about adding an inline fuel pump just to prime this thing. I like the Deuce fuel pump much better!

 

[KsM715]

I hear ya on priming those things after changing the filters. The TM says something like it should take 2 min. I bet I pumped mine for a good 15-20 min before my arm got numb.

 

[augiedoggy]

I like to use the mightyvac fluid evacuator to prime the fuel system on my 5 ton; just disconnect the fuel inlet line at the pump and put the mightyvac on the fuel line, and watch the fuel appear and bubbles dissappear as it sucks the fuel from the tank and filter.Then just quickly reconnect the fuel line......piece of cake! I prefer the air operated one, but hand pump works good too. Many other uses.....oil.....water.....whatever!

 

[cbvet]

I'm still having same problems. Rough idle & hard to start.
Checked all fittings, rechecked filter gasket.
I have a small Mightyvac I've used for brake bleeding & vacuum testing. I guess I'll try it on the fuel line & see if I'm sucking air in from somewhere.

 

[Floridianson]

As said check everything then take her out and run it to full temps. keeping the rpm up for a good run.

 

[area52]

You could try the ol' "pressure on the fuel tank" trick. Put a smal (1-2psi) amount of pressure on the fuel tank and see if any fuel leaks out of the fuel lines.

 

[sandcobra164]

Plus 1 on the fuel lines and plus 2 on removing the hand pump primer. Those hard plastic lines are primary culprit's for leaks. The cummins draws in about 1 1/2 the amount of fuel it really needs, the rest get's sent to tank. I've rehabilitated enough of these at this point that I replace all rubber and bypass all plastic anytime I'm tasked to pick one up and get it running. From a hard stab of the throttle and letting off, they do tend to drop to about 500 rpm for just a moment and then pick riguht back up. That seems to be the norm. Hard Starting, like more than 3 seconds is not. If it was a multi like in a Deuce, then 1/2 a second of starting is normal.

 

[5tondeuce]

I put a "T" with a ball valve in the fuel line right before it goes into the injector pump. After a filter change i hook a hand operated vacuum pump to the bleed with the valve open and suck up the fuel and close the bleed valve. It works so well you would not even know you changed a filter

 

[MyothersanM1]

I have spin on adapter for my fuel filter. As a security measure, I installed a locking ball valve on the fuel tank side of the fuel filter. An unintended use for this valve was to maintain prime during filter changes.

Upon removing the filter, I first close the valve retaining all the fuel in the line back to the tank. Prior to replacing the filter, I fill it full with fuel and screw it back on (use a catch bucket in case of spillage). So the only place I lose prime is from the front side of the filter adapter to the IP. I push the accelerator pedal to the floor and crank. A few seconds later the engine fires right up. BTW I got this all from a well known Cummins mechanic who lurks about these parts. Thanks WillWagner.

 

[cbvet]

Thanks very much for the tips!
I hope to have time to try them out this coming weekend.

 

[73m819]

Still sounds like your sucking air, look at the top of the fuel filter, make sure the little plate under the canster bolt is FLAT, will not seal the o-ring under it if bent, ask Tim, he knows what i'm talking about