Cm870 low boost high egt

[Oilysnowman]

Hi, I’m hoping someone might be able to help me with a problem I’ve got on my cm870.
It’s got RR programming
New turbo
New head
New cams and rockers
New fuel actuators
New turbo control module
Injectors test good
Recent overhead done
Passes all Insite tests

But here’s the problem, when it’s warmer then 0 Celsius, it works really well, colder then that, it works terrible. Low boost on pulling and engine brake (30-32 pulling 20 on engine brake).
When it’s cold out, I can block the radiators with cardboard, and it works very well empty, but loaded I have to let the coolant rad get some air, and by the time it has enough to sufficiently cool, the low boost problem is back. Egt run at 900-1000 when it does this, and it also has steady black smoke.

On Insite it shows EGR temp is a fixed100f
Ambient air temp is a fixed 72f
Turbocharger inlet air temp is a fixed 118f

All my other sensors seem to show correct readings, I’ve done the cold engine sensor compare multiple times, and they match.
Checked fuel pressure with a manual gauge and it showed 275 psi, Insite showed 255.

I’m sure I’m forgetting some info, but that seems to be the long and short of it. CN anyone help me with this? Thanks!

[tree98]

Has the imap sensor been replaced? Is the turbo a genuine cummins (holset) replacement or an aftermarket of some kind? Is the turbo control box a genuine or aftermarket?

[Rawze]

(01-22-2026 )Oilysnowman Wrote:  ...
On Insite it shows EGR temp is a fixed100f
Ambient air temp is a fixed 72f
Turbocharger inlet air temp is a fixed 118f

...

Those sensors do not need to be bypassed as part of a de-mandate.

[Oilysnowman]

(Yesterday )tree98 Wrote:  Has the imap sensor been replaced? Is the turbo a genuine cummins (holset) replacement or an aftermarket of some kind? Is the turbo control box a genuine or aftermarket?

The intake pressure and temperature sensors are both not very old. Doesn’t rule them out, but they seem to give correct readings.
Holset turbo
Cummins turbo control box, about two years old.

[Oilysnowman]

...
[/quote]

Those sensors do not need to be bypassed as part of a de-mandate.
[/quote]


RR looked into this issue for me, when he turned on those sensors we got egr codes.

[mikkhh]

E G R temp fixed at 100f, does not make sense to me in this case, that should read max temp instead on a deman so engine would default to non e g r mode (e g r overtemp)?

[Oilysnowman]

(Yesterday )mikkhh Wrote:  E G R temp fixed at 100f, does not make sense to me in this case, that should read max temp instead on a deman so engine would default to non e g r mode (e g r overtemp)?

I see…RR has put this tune in two cm870s that I work with, and they work flawlessly. I’ve had two previous demandated programs in my old ecm, but I put a new ecm on and RR copied my cab controls out of the old one to flash into my new one, any chance some bad programming could be in the cab control part of it that followed into my new ecm?