CM870 Jake Brake Issue
03-18-2021, (Subject: CM870 Jake Brake Issue ) 
Post: #1
CM870 Jake Brake Issue
I'm putting an updated stock cam in my CM870 and thought I'd see if anyone had any ideas on my Jake issue. When I bought the truck the 3rd stage of the Jake didn't work. I bought the truck that way and also had the truck tuned by a tuner recommended here. It still did not work and he didn't know why it wouldn't work. The truck has the stock VGT turbo on it which is nearly new. I did the turbo test using insite and according to the computer it passed. I could hear the turbo changing pitch and watch the actuator move. I also drove the truck with insite hooked up and according to the computer the engine never demands more than 70% closure of the veins. When I switch the brake switch from stage 2 to stage 3 there is no change in demand for the turbo to close down and obviously no change in the amount the engine holds back. I thought about the Jake switch being bad but when the switch is moved from stage 2 to stage 3 insite shows the Jake going to 100% so the switch is working. Even during normal driving should the engine demand more than 70%? It's like it hits a wall there, it goes to 70 and stops. Has anyone else run into this? Thanks!
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03-18-2021, (Subject: CM870 Jake Brake Issue ) 
Post: #2
RE: CM870 Jake Brake Issue
70% is above anything that turbo needs to make the jake go full on... and is beyond anything it needs to make 36-38 psi boost.

* Has anyone bothered to pressurize the whole engine up to 30 psi and look for boost, exhaust, etc. leaks?.

* Will the enigne pass an injector leak-down test?. If not, then the jake will be weak, as the injectors will leak fuel into the cylinders when they are not supposed to...


and...

* How many PSI is the boost showing under full jake brake?


.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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03-19-2021, (Subject: CM870 Jake Brake Issue ) 
Post: #3
RE: CM870 Jake Brake Issue
What RPM range are you requesting the 3rd stage? If you are an engine torturing low RPM (1500 and below) operator, that 3rd stage will never hold back anymore than the 2nd. 3rd stage works best in the 1500-1900 rpm range.
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 Thanks given by: Rawze
03-19-2021, (Subject: CM870 Jake Brake Issue ) 
Post: #4
RE: CM870 Jake Brake Issue
The engine makes about 15psi of boost when the Jake is on. No change in boost pressure between stage 2 or 3. It makes the correct amount of boost under load but I have not checked for leaks. I am planning on doing that though.
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03-19-2021, (Subject: CM870 Jake Brake Issue ) 
Post: #5
RE: CM870 Jake Brake Issue
At what rpm does it make 15 psi? Stage 2 jakes on my cm870 only made at most 10-12 psi.
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03-19-2021, (Subject: CM870 Jake Brake Issue ) 
Post: #6
RE: CM870 Jake Brake Issue
(03-19-2021 )Psuce1 Wrote:  The engine makes about 15psi of boost when the Jake is on. No change in boost pressure between stage 2 or 3. It makes the correct amount of boost under load but I have not checked for leaks. I am planning on doing that though.

Stage-3 jake on the 870 is usually about 26-28 psi at 1600-1800 rpom range.

the only differences between styage 2 and stage 3 is more restrictions beign commanded by the turbo.

-- possibly ...

* bad programming? or incorrect program for the CPL?

* Turbo was replaced at some point with incorrect model number (has wrong exhaust impeller in it for the CPL engine it is)?

* Turbo controller or control arm acting up?. 870's notorious for this.

* Problem with air supply line going to turbo?

- Can't rule out a jake solenoid or control circuit for one is bad either. Maybe try manually switching them on one at a time and see if they are operating correctly?.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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03-19-2021, (Subject: CM870 Jake Brake Issue ) 
Post: #7
RE: CM870 Jake Brake Issue
15 is the max I see at higher RPMs. Will insite say that the turbo passes it's test if the actuator isn't working correctly? Since it's air operated there isn't really a sensor telling the computer what is going on, unless it records the turbo rpm to establish the poison of the veins?

I didn't think about the turbo being incorrect, that's a very good point. I'll have to check the part numbers, especially since it was recently changed.

I the issue was the same before and after the tuning so hopefully that isn't the issue.

Thank you guys for the responses.
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