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Kbarnes0 · 08-11-2022, **(Subject: 870 boost )**

Under a hard pull 100% throttle, should boost maintain at peak level, until rpm slows due to the grade?

My boost varys quite a bit. Rarely do I see 35-36psi. Typically pulls at 32/33. Seems like it should hold 36+ consistently.

Rawze · 08-11-2022, **(Subject: 870 boost )**

(08-11-2022 )Kbarnes0 Wrote: Under a hard pull 100% throttle, should boost maintain at peak level, until rpm slows due to the grade?

My boost varys quite a bit. Rarely do I see 35-36psi. Typically pulls at 32/33. Seems like it should hold 36+ consistently.

What you are describing is the most common derate that CM870 engines get. It is very well known.

If the CM870 goes into a boost derate then the boost will typically jump up to about 36 psi in a pull, then fall on its face back to 30-32 psi. It is the most common derate those things will do.

This can happen because someone unplugged the egr valve or has defeated the egr in some way. EGT's also will skyrocket and this is very hard on the turbo.

Like I said.. It is a very well known condition with CM870's, and a person would think that after 15+ years of them being out there in trucks.. that some of the complete morons who are half-arsse making de-mandate (delete) programs for them would know this by now.. but that is not the case at all.

-= Someone's half-arssed delete programming that makes the check engine lights go away cannot fix that derate, but instead, typically only makes things worse by shortening the life of the engine due to garbage settings.

The problem is in the ram memory of the ecm, and not even in the programming itself. CM870's are special that way, and very few people understand them properly.

-=============

Forum member 'running rough' here on the forum knows how to program them and adjust those ram memory settings properly .. I trained him myself on handling this issue. I only do things thru e-mail (files only) and don't mess with CM870's, as they require someone to remote desktop to them.. and i do not do remoter desktop work. 'running Rough' does most of the CM870 engines for people on here instead. - Maybe PM him for some advice, etc.

If you have a de-mandate program in it then I would also suggest that you. or someone copies it from the ecm and e-mail a copy to me for a proper review so that you can find out if it was harming your engine internally.

Most de-mandate program are very harmful, all while the truck owner swearing it seems to run ok. Bad programming can shorten the engine life by as much as 75% and the truck owner never know it until it is far too late.

Kbarnes0 · 08-12-2022, **(Subject: 870 boost )**

Luckily, I've had running rough do the tune, which made a huge difference. Was hoping to to have a couple more things to check on my end before reaching back out. Is there a sensor that is the signal that may be the issue?

marek4792 · 08-12-2022, **(Subject: 870 boost )**

Depending on the year of your 870 the turbo control valve on the lower driver side under the air compressor are known to go bad for pretty much no reason at any time. Also check the system after it for any air leaks including the actuator arm.

Kbarnes0 · 08-12-2022, **(Subject: 870 boost )**

Good call, I've heard of the controller going bad. I'll check that actuator as well.

(08-12-2022 )marek4792 Wrote: Depending on the year of your 870 the turbo control valve on the lower driver side under the air compressor are known to go bad for pretty much no reason at any time. Also check the system after it for any air leaks including the actuator arm.

Bakanka · 08-13-2022, **(Subject: 870 boost )**

(08-12-2022 )Kbarnes0 Wrote: Good call, I've heard of the controller going bad. I'll check that actuator as well.

(08-12-2022 )marek4792 Wrote: Depending on the year of your 870 the turbo control valve on the lower driver side under the air compressor are known to go bad for pretty much no reason at any time. Also check the system after it for any air leaks including the actuator arm.

Good to check that, my had a corrosion on connecting plug it was not boosting over 30psi loaded or not. Plus the corrosion went inside that valve i had to buy new Air control vale plus replaced that connector to valve, and everything started working fine.

Kbarnes0 · 09-01-2022, **(Subject: 870 boost )**

Well, I'm still at it. Checked for leaks on the actuator, pulled it again since it had been awhile. Did the actuator test in insite. Everything is looking good. Connection's etc.

This is the variables I've noticed in the last few days. Out of Salt Lake, Im running into WY and CO on 80/25. Grossing 78k.

As I climb I notice boost falls flat at approximately 27psi above 1500 rpm. Grab a lower gear at 1400 and it will occasionally get to 29/30 and then back down. Egts follow.

Is this common for turbo diesel at high altitudes?

My plan is to continue on this otr run and see if anything changes.

When these pneumatic boost controllers act up, is it while driving typically?

Rawze · 09-02-2022, **(Subject: 870 boost )**

is it an aftermarket turbo or CAC unit?... Those can cause some problems like that too.

Kbarnes0 · 09-02-2022, **(Subject: 870 boost )**

Everything is stock other than the tune and block plates. Good flowing Donaldson muffler. Everything seems to check out.
When I got the truck the Holset turbo had just been replaced.

The front cover was resealed and new turbo and air compressor installed just before I bought the truck. Maybe the cam timing is off?

Just trying to figure out if I should still be reaching full boost at altitude.
Maybe I should put a gauge inline with the signal to the actuator that I can view while driving.

I'll see how it does today now that I'm empty.