2001 Freightliner Classic with N14 miss at idle.

Yeah I definitely should keep the idle bumped up. You are correct that around 800 or so it sounds so much happier. I wasn't sure what the intended idle for the N14 was from the factory. But at the 500-600 range that it defaults to my truck definitely idles worse.

 

I dont drive around with the idle at 800...it's more like 600-625ish. 800+ish is for long term idle. My truck's default idle is like 550...thats too low for the cam.

 

Since we’re talking about injectors in n14s have any of you guys had problems, I am wondering if cummins got a bad batch. I ended up fixing a cylinder on a recent o/h because of it and then he lost another one about 2 weeks later? They were the better ones from cummins themselves.

 

I haven't had any issues...knocks on wood...but I adjust the valves and injectors at least once a year.

 

From what I have read/heard, Injectors are hit and miss for all the older engines since they have been remanufactured so many times. Even if you get the OEM ones.

 

The idle “miss” has always been an NH series trait. Ever listen to an old small cam idle? It sounds like it has a high lift race cam in it and is hitting every other revolution. Gets more pronounced when the air compressor is pumping. I set all my old mechanical pumps to idle at 700-725 on Cummins. Cummins traditionally set the factory idle spec at 500 on normal aspirated and 625 with turbo to get a little more oil circulating through it. They idle better at 700-725 range. Less clatter and vibration. On some engines i fine tune the idle to be just where the mirrors or steering wheel shake goes away or at least as at it smoothest while at idle.

 

Also too. Just so you feel better about the thought of the idle being to high at 800. Cummins books have always considered to idle range specs. What they call low idle spec. It is 500-1000. And high idle which was 1800 to 2100 without load. So other than making a little more noise and using a little more fuel you aren’t hurting anything idling at 800-850.

 

Went through tons of non oem injector that did this exactly. 12 later installed oem and it went away.

Check pass through connectors. Unplug each one till you find the culprit. Could be faulty/dirty connection. They like to crack.

 

Thanks for all this information. I was curious what Cummins intentions for idle speed where. I'm honestly probably just going to set the idle to 800 or so and forget about it. Then this "miss" isn't even noticable.

 

A quick update on this thread. I was doing more poking around and the ECM grounding fuse is blown. Probably has been for who knows how long. It had a 15amp one in it. Is that the correct size? Going to grab some new ones in the morning when the store opens. Wonder if the ECM has been damaged at all due to the fuse being blown?