Prostar engine brake?

More than likely your engine brake harness is toast. It is located under the valve cover. In time they Harden and crack. You will have to remove the valve cover, a deep 10mm socket and ratchet will be needed to remove the cover. The gasket in the valve cover is reusable, just clean the surfaces when reinstalling. And do not let debris fall in to the head.

On the driver side of the head, between the 3 and 4 cylinders is where the plug is located for the harness. There is a metal clip/retainer that holds it in place, a pair of needle nose pliers works best to remove it, it will pull straight up and out.

Be gentle removing the harness inside the head, there are leads that attach to the actuators, that is where the harness normally fails, the leads get lose and brittle and fail. Those metal clips can be fragile, be gentle. The new harness will go in the same way the old harness came out. If you have to force the legs into the head, that is normal, you will not hurt anything to give that a little muscle. The plug end of the new harness, it goes through that hole in the head, lubricate the o ring with engine oil or petroleum jelly (Vasoline) before installing. And make sure the plug is seated in that hole, make sure the retaining clip on the outside of the head sits in its proper place on that plug. If not, you will get an oil leak.

And seeing as you are right there on the side of the head, I would replace the cam shaft timing sensor, it is the sensor to the front side of the brake harness. It to mounts into the head. They are inexpensive and easier to install when you are doing the brake harness. Get two, because down by the damper, below and in front of the air compressor is the crank shaft timing sensor, it is the same as the cam shaft sensor. I would replace both. They are held in with one 10mm bolt through a bracket that is attached to the sensor. Good time to do those too... They do go bad in time, I would say it is time if your brake harness is toast. Time to replace, good preventative maintenance.

I think the harness runs around $100, it is a normal stock item at Cummins and most dealers that sell Cummins parts. Those timing sensors are around $25.

If you are in there, best to do an overhead. Rawze.com has a video on the procedure. You should do this every 250,000 miles. I bet yours has never been done. Good time to do it when replacing this harness.

Here is a photo of the harness...



Here is a photo of the cam and crank timing sensor...



Here is the video on the overhead...

 

It is not that difficult, first time it takes some time. I would recommend getting one of these for the exhaust brake adjustment... https://www.amazon.com/CUMMINS-ENGINE-BRAKE-ADJUSTMENT-TOOL/dp/B076DKS9YK

One of these to adjust the injectors... https://www.amazon.com/Performance-..._rd_t=40701&psc=1&refRID=VWEZWQPXYD41MV53P097

You will need one more torque wrench for the valves, best to use two, each set to the appropriate torque, less chance of screwing up. I use a Tekton and a Crafstman for the valves.

The rest is pretty much self explanatory in the video.

A shop will charge around $400 to do an overhead, you can put the tools together for a fraction of that. Good way to learn your motor, and it takes some intimidation out of things when they go wrong.

You will need something to bar the motor...

A set of these... https://www.amazon.com/gp/product/B000VAQNPA/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

And one of these or something similar... https://www.amazon.com/Z-Red-Drive-..._rd_t=40701&psc=1&refRID=6QA2YQ56Y3FPRKGVBAJD

 

Can't the selonoids go bad also? I've had bad ones on Detroit's before.

 

Not really, it is rare for the actuators to fail. When you open up the top of the motor, it will be easy to see if the harness is the issue, the clips on the actuators will be lose or cracked. In time, from the heat of the motor, the connections fail. Common problem with all engine brake equipped ISX motors.

And don't be afraid to open the motor up, just keep any debris from falling in there. Removing the cover is a very easy to do task. You may have to cut some zip ties to move the harness, just have a bag of zip ties on hand.

I get mine at Fleet Pride, the zip ties. They have the ones rated for high heat and low temps, much better than the ones you get at say Menards or Home Depot. If you don't know about Fleet Pride and own this truck, it would be a good idea to see if you have one locally. They are a fantastic place to buy all sorts of parts and fluids for your truck. Prices are always less than what the dealer charges.