CM870 Turbo Underspeed and Overspeed

[pwhittle]

Hello,

My CM870 (factory stock) ISX15 525hp has been derating with Turbo Overspeed (max 32 psi boost) for a while, and has just started throwing Turbo Underspeed codes at low speeds. I first noticed it in some stop and go traffic on the last trip.

I have Insite and some logs of the Overspeed, but have not logged the Underspeed code occurring yet.

What should I be looking at?

Thanks

Paul

[tree98]

Boost leaks could cause the over speed.

[marek4792]

Boost and exhaust leaks, mine did this even after a Demandate and it drove me up a wall...

[Rawze]

Maybe some history on it?>.// is the EGR valve unplugged?.. etc.

Can be a lot of things, including a derate for the egr system not working properly.

[pwhittle]

Serial number is 79079781. 2004/11 manufacture date in a 2005 vehicle.

Engine has 120k miles on it. Overhead done by Mr Haggs in 2017 at 80k miles.

Exhaust manifold recently resurfaced as a bolt had broken. EGR cleaned out at the same time.

The turbo underspeed code in stop/ go traffic is new after the exhaust manifold repair. The turbo overspeed derate was present before and after.

Paul

[Rawze]

(10-05-2023 )pwhittle Wrote:  Serial number is 79079781. 2004/11 manufacture date in a 2005 vehicle.

Engine has 120k miles on it. Overhead done by Mr Haggs in 2017 at 80k miles.

Exhaust manifold recently resurfaced as a bolt had broken. EGR cleaned out at the same time.

The turbo underspeed code in stop/ go traffic is new after the exhaust manifold repair. The turbo overspeed derate was present before and after.

Paul

Did anyone bother to replace the EGR Delta=-P sensor and clean out its pipes, etc?.

Did anyone change the program in it to another program (to change the horsepower, etc)?.

How old is the turbo?

... and did anyone re-clock the exhaust housing and ensure the turbo was not sticky after the manifold replacement?.
here is some related info on this: http://rawze.com/forums/showthread.php?t...8#pid54418

Anyone replace the turbo speed sensor and check wiring for it to ensure they are good?.

Anyone test the turbo to see if the actuator is hanging up.. or is not smooth while the actuator is off of it?.

Anyone check/test the air operation and air controller for the turbo actuator?.


and last but no least at all.. How old is that muffler on that truck>?.. because those mufflers clog up on those trucks, or get restrictive after several years, and cause turbo issues too.


Like I said.. it can be a lot of things on those CM870's because they had that air operated VG turbo controller on them with n feedback to the ecm for positioning.

[pwhittle]

Thanks Rawze,

Stock software, as far as I know. I am second owner. First owner would not have messed with it.

It is the original turbo, with 120k miles on the engine.

Muffler was recently replaced with an Aero 5050XL.

I’ll take a look at the actuator.

Would there be readings in Insite that would confirm which sensors that need replacing?

Paul

[Rawze]

Sensors on CM870's usually do not tend to fault unless they are really far out of whack or disconnected.



I have seen people get 3 as low as mpg and not a single fault in the dash even though their intake pressure sensors was whacked and causing it.