Cm870 drivability woes

[DrDave]

Hi, newbie to the forum here just looking for a second opinion on this cm870 I’ve been trying to sort out

Backstory: Cummins recon cm870 cpl8518 565hp was dropped in this truck 3000h ago, since then it had a whole pile of work done on it including a head, injectors and fuel/timing actuators and somewhere along the way the egr had fell off also

I’ve got the mechanical side sorted out, it had another injector with a bad metering check valve and opposite bank timing actuator. But it still has some quirks to it that I believe are just tuning related now. At idle most of the time it will command very low turbo speed and start to haze, then for no good reason or when the idle is elevated it will kick up the turbo to ~20k and purr along nicely. During shifts there is usually a lag, almost like a dead spot when you get back on the throttle. Driver says it lacks power from what it had before the butt sniffer fell off

If anyone (rawze?) would be interested in taking a peek at the cal just to confirm my suspicions that would be great. I’m by no means a tuner but I can find my way around the software well enough that I’ve done some tinkering on my own stuff that hasn’t blown up, I’m just not comfortable making the call on someone else’s engine. Also what I’m seeing is not at all the way I’ve been taught and self learned how to make the butt sniffer go away

What I’m seeing in the file that really sticks out to me:
-mass charge flow tables flat line to “2” in the lower quadrants
-density fuel limit just spikes at 1500rpm and flat lines
-post injection removed
-fair bit of timing added in places

[tree98]

You can bet your ass its a bad tune. The problem is that those 870 ECM's aren't easy to play with, they brick quite easily. As far as I know, the only guy on this forum that does them is runningrough. Maybe send him a PM.

https://rawze.com/forums/member.php?acti...le&uid=993

[DrDave]

Thanks I’ll pm him.

I’ve had my share of fun with these over the years and yea even had one shi#t the bed on a stock cal update via insite. Was able to recover it with CT easily though. I’ve even been ballsy enough to flash them more than a few times with CT

[Rawze]

STOP fighting garbage programming...

FLASH the ecm back to its original factory programming that belongs in that engine according to its ser# and unplug the egr temp sensor. This will let it run correctly,.. no 'TUNE' needed.

ppl have driven CM870's a million miles like that without any issues or power/torque derate whatsoever. CEL light will be on, but this does not cause any issues. - Boost will also be slightly less 32-33 psi or so, but that is fine,.. does not hurt it or take away its power//torque output.

... run it that way for a while so that you can isolate all of its issues and get the engine back right mechanically... running really well. Get a base-line of how it should run... and fix any issues that it may have.

[DrDave]

I’ve done that with one that was still “intact” and yes of course it runs ok, do they not get pissed off without the valve connected?

[Rawze]

(03-23-2026 )DrDave Wrote:  I’ve done that with one that was still “intact” and yes of course it runs ok, do they not get pissed off without the valve connected?

it will run even if valve is disconnected.