CM870 VGT Actuator

[Lonestar10]

My dads 2007 T600KW CM870 popped up with some codes for the VGT air actuator and it wasnt working correctly so it was replaced. New OEM air actuator put on now he says his boost doesnt go as high as it used to when pulling only gets up around 30-32 where it used to run 35-37. Truck is a bone stock cummins 500/1650 Tune only thing changed was the air actuator. turbo was replaced last year in the spring.


any ideas? thanks for any info!

[Nilao]

Environmental? Mine will only hit 32 at times depending on the weather...i think it has to do with ambient temp, barometric pressure, etc...

[Lonestar10]

he said in the sub 0 temps he was only doing 35lbs but above 0 he said he would be in the above that.

[Unilevers]

its a well known failure of newer stock cummins 870 cals. They underboost when cold and cummins knows about this and refuses to fix it. only way around is to get it tuned out.

[Lonestar10]

the tune is about 3 yrs old or more i dont remember when he upped to 500HP maybe it was even longer ago when he was doing RGN. he was in 50 degree weather in denver earlier this week and said it was still low from before.

as far as tuning it out hes not as open to breaking away from OEM he wasnt even comfortable with me demandating my truck myself instead of paying some shop that he knows other drivers have gotten work done at as far as demandating. ill say even i was a bit apprehensive about some random guys i dont know getting my rig right over the internet. i wont say i agree 100% with some of the stuff our host goes off on but a good portion of it i whole heartedly agree with and understand. and as far as programming ive come to understand it more from others posts and asking my own dumb questions.

[Chamberpains]

What were the codes for the actuator? There are no direct codes for the actuator itself failing because it is 100% pneumatic with 0 direct electrical feed back.

A very common problem of the actuator control module failing will throw a lot of things out of whack. This module does throw codes when they fail completely. It's an expensive little thing but they do fail by commanding the wrong amount of pressure to the actuator. Do not go to ebay for a cheaper reman 1 if you decide to replace it, they are junk and piss poor remans. 100% new holset unit is the only way to go and even they can be wrong right out of the box but they are by far better than the half-assed reman crap they're pushing elsewhere. Call around to dealerships or wherever for the beat deal. Usually range $800-$1000

Also be sure there are no leaks in the plumbing to the actuator. The smallest pinch, kink or leak will result in off boost levels.

If you haven't checked yet, check your CAC circuit for new leaks.

[Lonestar10]

He got new from kw $850

[Chamberpains]

What was new? The actuator or did he get a control module? Your original post says he replaced the actuator on the side of the turbo and the turbo is a year old.

[Lonestar10]

the air control module that controls the VGT sorry. the entire Turbo assembly was replaced last year.