Cummins NHC 250 High Idle Problem

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WillWagner

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If there is an issue of taking air it will be on the suction side. Eliminate the truck to see if it is a pump or truck issue.
 

travistodd1

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If there is an issue of taking air it will be on the suction side. Eliminate the truck to see if it is a pump or truck issue.
I probably wont have time to mess with it this weekend, but I plan to run a line straight from the pump to a fuel can of fresh diesel and see what happens. If I still have a high idle problem, I suspect it is in my pump. If that is the case, what would I need to look at on the pump to start trying to fix the issue?

Thank you,
Travis
 

sandcobra164

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The one time I had an issue with my pump I pulled it off and had a reputable local shop rebuild it. It came to $360 if I remember so definitely not a deal breaker.
 

travistodd1

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Thank you all for your help and suggestions. Things have been crazy at work and other obligations have prevented me from spending the time on it I needed to.

I went outside and ran a line from the pump to a fuel tank with fresh fuel and it still has the high idle problem. Where should I look next? The pump is a new unit but I suppose it could still be the problem. Is there something upstream of the pump I should look at?

I would like to add something to the mix, I have noticed when I used the hand primer on the dash, it is quick to bleed off pressure. Is that normal or do I need to start tracking a problem. I do know the gauge needs replaced as it tends to fill up with diesel but I can't find one.

Thanks again,
Travis
 

simp5782

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The pump controls idle. So something with the pump is the problem.

Sent from my SM-G975U using Tapatalk
Sucking air causes a high idle. So does a restricted return

For the op. I assume you replaced the canister fuel filter and its seal. Did you replace the o ring on the bolt as well?

Do yourself a favor and delete that primer pump and put a plug in that 90 degree fitting at the rear of the pump. A proper running engine doesn't need that even if you do a fuel filter or a whole injection pump
 

travistodd1

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I am really hoping it isn't the pump although with my luck.... I will start tracking the return line and see what is going on there. It is also a real possibility that I have a restriction somewhere along the line.
 

WillWagner

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And remove the return line and drop it into a bucket, If the return line is plugged solid or kinked, the engine might not need to idle before the idle comes up, the line will be full and easily pressurized at start up to make the idle high. Do this before removing the pump. With a line into a clean fuel supply and the return disconnected as well as the linkage, if the idle is still high, most likely the pump. Never seen injectors cause it.
 

sandcobra164

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I would disconnect and plug off the primer pump as suggested. Air can get sucked in from the primer pump and you've said the one on your truck bleeds off pressure quickly. I've had quite a few trucks with an NHC 250 engine do exactly what yours is doing from sucking in air from the cannister filter Simp referenced as well. It doesn't take much air at all to make the injection pump unstable. You eliminated one source with your fuel delivery method, now eliminate the primer pump and report back.
 

Bill Nutting

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I had a problem with my truck loosing it’s prime. I put an electric fuel pump on it right at the tank. It started right up. Then I noticed a fuel leak. One of the plastic lines on the pump had a split. In was on the suction side so it didn’t leak until I put pressure on it. Replaced the plastic line with copper, un-installed the electric fuel pump and all is well. The lesson I learned was pressurize the fuel line at the tank and look for leaks. You will see a fuel leak where there was an air leak.
 
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