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Curtisj28 · 02-21-2020, **(Subject: 07 870 Jake issues )**

2007 cm870, 700hp heavy haul application running a hx60. Yes I understand I lose 3rd stage. No I'm not putting vgt back on at this exact moment. Considering it in the future.

I am having issues with my Jake brake. It will work great after idle when engine temp is down but when at full temp it is very weak and choppy. Boost levels range from 12-25 depending. Higher RPMs usually help but when it hits 15-16 you can hear and feel it change. If I go to stage 1 you can hear it but does virtually nothing and completely stops around 1300. And you can just hear a slight noise from valve cover. Has been an ongoing issue since purchased 400k ago. Truck has 1.3 total. 45-50 on O/H from Mr hagg. Uni tuned also. My rocker shafts and arms all around are new. New Jake harness. New head. I don't remember if we did solenoids or not. It is a 2 solenoid system. Maybe the #1 solenoid? Insite shows all 3 stages when the switch is flipped but for some reason full up is 100 middle is 33 bottom is 66. Any ideas?

Chamberpains · 02-21-2020, **(Subject: 07 870 Jake issues )**

If this is in an International then that is the correct position "stage" sequence for the jake. Top =3 (high) Middle=1 (low) Bottom =2 (middle)

Cummins quickserve has the test procedure to ohm out the solenoids. Also make sure your harness is make good contact at the solenoids. They are just push on connectors. Also check to make sure the passthrough connector isn't filling up with oil internally. Pull it apart at the head and have a look. If it is, you can clean with brake clean and seal it up with high temp RTV.

http://rawze.com/forums/showthread.php?tid=5734

Curtisj28 · 02-21-2020, **(Subject: 07 870 Jake issues )**

It is a peterbilt 379. The main thing that has me stumped is that engine temp affects it. I'll check the passthrough connection

Rawze · 02-21-2020, **(Subject: 07 870 Jake issues )**

What is your oil pressures cold vs. when it is warmed up and weak?. On an old engine, it could be starving if oil up top after it gets warmed up. Also might want to open valve cover and inspect while engine is running to see if there is something bleeding oil badly in the top-end (spun bearing, loose retaining bolts, excess play in rocker bearings, etc.).

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I am sure others have said this too, seems you already know this aas seen in your first post ... Just putting it here for reference for others who may not know ...

With that non-vg series turbo installed, the jake will always be weak (like he mentioned), as the 3rd stage jake on the ISX IS IN FACT mostly reliant on that VG turbo back-pressure for it to function correctly.

Here is how they work...
Stage1 == only one solenoid fires (3 cylinders).

Stage2 == BOTH solenoids fire (all 6 cylinders).

Stage3 == BOTH solenoids fire AND THE VG TURBO is used to generate a severe restriction in the exhaust manifold (+ extra intake boost pressure), forcing exhaust gas to move from one cylinder to the next, and get re-compressed a second time, dramatically increasing the engine breaks strength.

So... Without a VG turbo on it, stage 3 is pretty much 100% defunct, stage 2 suffers greatly in its strength, and stage 1 just about operates normally.

Curtisj28 · 02-21-2020, **(Subject: 07 870 Jake issues )**

(02-21-2020 )Rawze Wrote: What is your oil pressures cold vs. when it is warmed up and weak?.
...

It is right around 36-37 warm at 1500

Rawze · 02-21-2020, **(Subject: 07 870 Jake issues )**

(02-21-2020 )Curtisj28 Wrote:
(02-21-2020 )Rawze Wrote: What is your oil pressures cold vs. when it is warmed up and weak?.
...

It is right around 36-37 warm at 1500

then it is not likely an oil-pressure related issue it sounds like, unless a cross-channel has gotten clogged up. Still though, I would look for hemorrhaging up there just to be sure.