Idle at 750 rpm-normal?

[Andyba20]

From reading it seems normal idle for our trucks in park is 800-850. Mine idles smooth at 750, and I’m pretty sure it always has. Been paying closer attention to the truck as I try to figure out this low boost issue and some other little things. Truck starts right up, 1/2 a crank at 20F this morning. My concern is the Nations 180 amp alternator. Just making sure this isn’t effecting performance on that. Is 750 in the acceptable range? That’s 750, no ac. Auto trans in park. High idle kicks in as it should. 

[Mopar1973Man]

Normal park/neutral idle speed is 800 RPM +/- 5 RPM. If your idle is high means the ECT Semsor is actually reading lower temperature than it should. If it idling low typically the injectors are wore out. Most injectors are about 100k to 150k miles. This should be regardless of loads. When the APPS triggers idle mode the APPS value is dropped and the Cummins idle software is used. It's set for 800 RPMs you should be able to have everything on and sit at 800 RPM. If your live data shows ZERO engine load the injectors are wore out. ECM can no longer cut fuel to hit target idle speed.

Edited February 1, 2022 by Mopar1973Man

[Caleb Hardy]

My truck idles at 750rpm as well. Have you had any luck figuring out why it does not idle at 800rpm? 

[wil440]

On 2/1/2022 at 11:32 AM, Mopar1973Man said:

Normal park/neutral idle speed is 800 RPM +/- 5 RPM. If your idle is high means the ECT Semsor is actually reading lower temperature than it should. If it idling low typically the injectors are wore out. Most injectors are about 100k to 150k miles. This should be regardless of loads. When the APPS triggers idle mode the APPS value is dropped and the Cummins idle software is used. It's set for 800 RPMs you should be able to have everything on and sit at 800 RPM. If your live data shows ZERO engine load the injectors are wore out. ECM can no longer cut fuel to hit target idle speed.

Have a got it wrong then as I though I read here several times when injectors are worn idle increases ???

[Caleb Hardy]

That is how I read it as well. But I failed 4 years of English in high school hahaha

[Tractorman]

3 hours ago, wil440 said:

Have a got it wrong then as I though I read here several times when injectors are worn idle increases ???

 

I have never quite understood that relationship.  I ran my original injectors for 303,000 miles - performance was still fine, fuel economy still very good, and idle speed the same (right at 800 rpm) throughout the life of the injectors.  

 

- John

[wil440]

17 hours ago, Tractorman said:

 

I have never quite understood that relationship.  I ran my original injectors for 303,000 miles - performance was still fine, fuel economy still very good, and idle speed the same (right at 800 rpm) throughout the life of the injectors.  

 

- John

Far as I know ijectors in my truck haven't been changed and it's at 178k , idle is around 850 fuel economy is ok,  but with the £ nearly at parity with the $ injectors in my truck will not be getting replaced any time soon nor will anything else for that matter if I haven't got it on the shelf.

When I first got into American cars/trucks it was nearly $2 to the £ that made parts costs ok

 

I can see the reasoning that injection pressures will fall off as the miles or better still operating hours increase,  that is a given