Power surge on CM870???

[cowboycurtis]

A little background first. 2007 Peterbilt, 1,000,000 miles. Previous owner deleted EGR but didn’t touch the ECM. I found a lot of help here and now it’s properly tuned to 500HP with help from Momma Burt and others. No check engine light or major problems of any kind right now.

The issue is going up through the gears and putting down a lot of power it will just act like a dog. I grab a gear, put the pedal down and it climbs slowly up to 1750-1900 and that’s it. Sometimes I’ll grab the next gear and the truck is like a rocket. Tons of power and the RPMs will shoot up to 2100. It’s like a a rocket with 150 more HP. Then grab the next gear and it’s doggy again. The engine isn’t missing. Sounds good. Just runs out of power way early. Any ideas what is going on??

[Rawze]

what is the boost gauge doing?

BTW: those engines are not supposed to be driven like a 'rocket' .. It is abusive and turbo lag and everything else is going against you. Especially on an 870, as the turbo is air actuated and sometimes you get a little more or less because there is no feedback for the turbo position.

what your doing sounds just like your fighting unpredictable amounts of turbo lag. That is the nature of an 870 with a turbo (or controller or air actuator) that is getting worn and starting to hanging up a bit. Does not hurt a thing is you drive it normally, and the lag will usually always catch up to it.

it ain't no damn race engine! ... ESPECIALLY if it has a million plus on it. - I guess the notion of sending a piston thru the block due to age, a million+ of wear, etc. and pushing it so hard like that hasn't occurred to you yet.

Drive it gently ... drive it by the boost gauge, keeping it to 20 psi or less, ... and she'll continue to make money for you a year or 2 more ... otherwise, I hope you got a spare engine laying around.

[cowboycurtis]

I wasn’t trying to drive it like a rocket it’s just something I noticed. Turbo hangs around 30 psi either way under load. Actuator has been replaced recently.

[Rawze]

30 psi is too low for a cm870/cm871 under full load. Should be around 36-38 psi or so at full power.

[cowboycurtis]

I’m guessing it needs a new charge air cooler. Previous owner said it’s never been replaced. 1 million miles is a long time on a charge air cooler. Turbo has 150,000 miles and I replaced actuator and air line. I’m second owner. What’s your thoughts?

[marek4792]

(05-02-2020 )cowboycurtis Wrote:  I’m guessing it needs a new charge air cooler. Previous owner said it’s never been replaced. 1 million miles is a long time on a charge air cooler. Turbo has 150,000 miles and I replaced actuator and air line. I’m second owner. What’s your thoughts?

Check your actuator rod for smooth travel by using a 10mm and turning it counterclockwise like you're trying to loosening the bolt, There is some spring force to overcome but should be fairly smooth if it's very tight to the point you're loosening the bolt or you feel it hanging up it wouldn't hurt to replace the turbo. On mine I had rebuilt had a fixed VG ring and it would hang up due to the alignment of the turbine housing and bearing housing causing very similar symptoms. One member caught their actuator rod leaking air when it would extend to full travel as well.

[JimT]

(05-02-2020 )cowboycurtis Wrote:  I’m guessing it needs a new charge air cooler. Previous owner said it’s never been replaced. 1 million miles is a long time on a charge air cooler. Turbo has 150,000 miles and I replaced actuator and air line. I’m second owner. What’s your thoughts?

Do a charge air pressure test and find out exactly where your leak(s) are. Could be multiple little leaks, you won't know until you test the system.

[Chamberpains]

I had an air actuator leak at around 40٪ clear up to 60% then it would seal again.

Pull the actuator off and feel how smooth the armature moves. It should be slightly dry metal on metal squeaky but smooth for a full 10mm. If there is any snag spots or sticky in any spot you'll probably be looking at a turbo swap.

If this is the case YTS in Georgia did a fantastic reman for me and the price is right compared to any OE price

[4lanefarmall]

cowboy, I'm interested in what you found! I'm having exactly the same issue. and guys its not that he's driving it like a rocket, (at least on mine) when going thru the gears its really sluggish and then out of the blue without changing pedal position it will throw u back in the seat instantly and reach shift point ( as if you were in a rocket) and I noticed lately that it is running higher boost on flat roads like 20 to 25. It still achieves full boost (about 37) but takes longer to get there