Skip to main content ↑ ↓
Topic: Setting low idle (Read 1121 times) previous topic - next topic

Setting low idle

(I did a search and did not see this topic but surely I just missed it.  Sorry if a repeat. If you make the adjustment, be sure it is safe for your coach and you.)

I felt that the idle on our engine was too low at 600 rpm.  At too high an idle though I had found that it really pushes on the coach when trying to stop.  Even at 750 rpm for us is a little much, so probably 700 - 725 would be better for us.  I think our idle had gotten to 600 rpm by some technicians to get me out of the 800 rpm idle range we had had or adjusted down just by accident.

Given that, how do I move it up from that 600 rpm to the 700/725 rpm for low idle?    I found from Mike Rodgers that if I put the coach in N and at idle, I can adjust (set) the idle upward in about 25 rpm increments by a quick press of the SET  button on the cruise control.  A neat trick, not some screw to adjust like on a lawnmower!  (I think that to lower the idle I press the resume button but have not tried that yet.)

This only works on engines with computers (electronic controls) and I do not know if it works on all models of those.  You might give it a try if you want to experiment with idle adjustment.

Note this is different than going to a temporary high idle to warm the engine in which you use the cruise on/off button with the set button. 
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Setting low idle

Reply #1 –
Mike,

Actually, the use of the cruise to boost idle speed (for faster engine warm up and quicker air fill) goes back to the old mechanical engines as well.

I would check with Cummins on setting your low idle speed.  The use of the cruise control to boost RPM should be viewed as ABOVE low idle speed.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Setting low idle

Reply #2 –
Bret, thanks.  Unless someone has answers already, I will call Cummins in the morning.  I was told that this only worked on electronic engines as a setting mechanism beyond the momentary boost.  But I surely do not know about that, can only repeat what I learned (was told) and tried.

I had that 825 rpm low idle and complained.  Service folks said that was high and then set it to 725 but after some time, probably a month or more, I was at 600  rpm.  I had no idea how I got to that.  After hearing how this worked I began to wonder if I happened to have hit the resume button when not in cruise and so I was setting the low idle down to the 600?  Just a guess.

Maybe it is best no others try or use the method I described until I get Cummins on the phone.  In the meantime, how do you (we) set the idle on the engine?  Like I said, I know how to change the idle on a lawnmower, well and a four-wheeler too, but not on these diesels.  Maybe a shop has to do this via the engine computer (and not me using the cruise buttons)??
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Setting low idle

Reply #3 –
I set my idle at about 675 rpm, this low idle can be set between about 550 and 950 rpm adjustable and the normal Cummins HIGH idle at 1200 rpm, non adjustable.
No clue about the setting on a non electroic C8.3.

Dave M

Re: Setting low idle

Reply #4 –
I got Cummins but they did not know the answer on first try.  So I called Mark Harvey at FOT.  He said that he had forgotten how to do the adjustment as I described but it is what you do (see start of this topic) though only certain engines or systems will allow that.

I may try again with Cummins but since Mark said it proper, and two other technicians, and I gather Dave M did  not disagree, I am going to use this.  A neat trick if I am not harming something!

Mark said for my ISM I should be around 725 rpm low idle.  I am going though to try Dave M's 675 or 700.  725 still pushes it along a bit more than I need.  I guess it does not harm the transmission or such at 725.

Have a good day folks, Mike
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Setting low idle

Reply #5 –
Don't worry - you'll know if you're not low enough. You'll stay in neutral.
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: Setting low idle

Reply #6 –
Dave is correct.  If idle speed is too high, the Allison is programmed to NOT go into gear and the shift pad will just "flash".
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Setting low idle

Reply #7 –
My origional idle rpm was high enough to slide the front wheels on icey/snow covered area, had to really press hard on brake pedal to stop rear wheels from turning, that is when I got into lowering the idle speed from what ever it was to a manageable rpm, so why I now use the 675 rpm area.  Also does not tend to heat the transmission temp while at a long traffic light etc.
It is another learning experience, aint't it ?
Dave M

Re: Setting low idle

Reply #8 –
It would be nice to know what the alternator output is at that RPM on comparison to the higher value. That would be my only concern.
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: Setting low idle

Reply #9 –
Quote
My original idle rpm was high enough to slide the front wheels on icy/snow covered area, had to really press hard on brake pedal to stop rear wheels from turning, that is when I got into lowering the idle speed from what ever it was to a manageable rpm, so why I now use the 675 rpm area.



So how do you lower the idle speed?  I'm at 750 and you better have the brake pedal pushed hard because it is ready to go.

Thanks,
Brad

2000 U320 4000

Re: Setting low idle

Reply #10 –
Hi Brad,
On the ISM, just using the RES to increase and the SET to decrease works on mine.

Seems you can go from about 500 to 900 rpm area for idle, do not recall the exact limits, if your sitting still in neutral and park brake on, press ON/OFF then RES, mine goes to 1200 rpm.
I like it, another reason I like the computer version vs the mechanical, have zero clue how to work on these electronic wonders but I like them.  ;D

Dave M

Re: Setting low idle

Reply #11 –
Brad, that was the subject of my original posting....to raise the speed, put set.  Push resume to lower.

I do this in N, park brake on. 

I gather you may be able to do this in other operating conditions and I do not know if it works on any engine besides the ISM but some folks do tell me it works with almost all electronic engines.  Just give it a try.  I imagine I got to too low an idle by hitting the resume button when the cruise was not on and I was going down the highway thinking I was going to resume speed.  That is just a guess, trhying to explain how I got down to the 600 rpm in the first place.

As for me. 750 rpm was too much, hard to stop without really hard push on brakes.  I think even the 725 that I raised it too may be a tad high so will follow Dave M, drop mine to try 700, maybe to 675.  But 600 rpm was too low.

I posted this just thinking it was a neat trick.....how to raise/lower normal idle.  I did not know how nor see it in literature. 

I must say though that I had not thought about RPM/Alternator connection.  Still, even for that for me, I think the 600 was not so good. (If this is not clear, send me a PM and I will send you a phone number and we can talk but I think between all of us now on this thread you probably have more concise guidance than with what I began and are making progress!)

Good luck,  Mike
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Setting low idle

Reply #12 –
Howdy Mike,
Thanks for figuring out this important procedure and posting for all of us to see and use...
Dave A
Dave and Nancy Abel
'00 U320 36' WTFE  Build #5669
'10 Jeep Wrangler Unlimited Rubicon
Livingston, TX  SKP's Fulltiming
 

Re: Setting low idle

Reply #13 –
Mike,
Thanks for the information.  I will try this afternoon while I wash the coach.

Brad

2000 U320 4000