Isx repairs

I'm a bit confused let me run this down right quick:

1. Brakes weak before shop visit
2. Technician tests both solenoids
a. Was test performed with engine operating or engine off?
3. Operated unit will all connections made and checked brake operation, front set weak
a. Did technician check brakes on road test or sitting in the shop and throttling the engine?
4. Tech checks harness from ECM and it has correct power
a. How did he check the power? Through the DVOM test ports on the tester?

I agree with Nasriza probably just one of the 3 o-rings on the solenoid has lost its sealing ability or the solenoid is going bad itself. But I do like to check all my basis before putting parts on.

 

We see this all the time, the rocker shaft detent holes wear, go out of round where the jake control spool sits in it. this is were oil pressure is lost causing weak jakes. Replace both rocker shafts, all 6 control spools and 6 springs and it will bring jake performance back to new spec. cost is around $600 (cdn) and two hours time with a full valve set. cummins did a change up on the shafts to make them harder, so they last a bit longer. sounds like all your other checks show good.

 

What year/series is your engine? The jake's function is greatly effected by the turbo... do you have a vgt turbo?

I had my cams replaced recently and now EVERYTHING leaks that they took apart.

 

I was just thinking about that after sending my last post, the 870 will have the air operated VGT that can have it's own issue with leaks, sticking etc. the 871 will give you a code if there is an issue.
Also to check the jake rocker to see if the detent is worn, with the cover off, rock the jake rocker back and forth to "feel" if it seats into the detent firmly, if it flops around the detent is worn, will only take one hole per shaft to weaken jake output.

 

The terminals inside the connector to the pass through could be weak, or the wiring is partially broken in the harness. This would show ok with an ohm test, but the wiring and/or bad connection cannot pass enough amperage to fully trigger the solenoid. I would run new wires and terminals from the ECM connector to the pass through connector and try again.

 

Any decent shop will have a spare test ecm they could plug in to test whether you have an ecm or harness problem. ECM's are too expensive and non returnable to be guessing around. Another thing, some engines have 2 brake solenoids and other have 3. You need to make sure the calibration revision in the ECM is programmed with the correct number of brake solenoids.