Exhaust Brake / Turbo Boost problem

[Greg from Pittsburgh]

While traveling back from Huntington Beach NC. for spring break (beautiful state park btw), I turned on my exhaust brake only to have my turbo shut down. At least that's what I think happened, the gauge on the dash went to 0 ant the exhaust temp gauge began to climb and I lost all power. I pulled off to the side of the road, turned the exhaust brake off, idled for a few minutes and the exhaust temp. came down and the boost gauge began to show some life and the engine ran fine. I've never felt or herd any difference when using the exhaust brake so I tend to leave it in the off position. I've checked the lever on the exhaust manifold and it moves freely, any idea how the two are related?

[EngineerMike]

If you lost boost under all conditions I'd say you blew the charge air cooler open, or blew a line on its way between turbo & engine air intake. Getting boost back has me in a quandary. Do you think you have full boost returned or only partial?

[RustyJC]

You don't say whether this is an OEM (i.e., Jacobs) or aftermarket (i.e., Pacbrake) exhaust brake. The OEM-type brake gets its activation signal from the Cummins ECM while most aftermarket brakes get an activation signal from a throttle position switch - if you have the brake turned on, when you let off the throttle, the exhaust brake activates.

If it's the latter and the brake activates as soon as you turn it on, regardless of throttle position, I'd look for a problem in the throttle position switch or its wiring.

Rusty

[Dave Fernandez]

Hello Greg:

If I understand correctly, when the exhaust brake (Pac Brake) came on you lost power when you attempted to accelerate back to normal speed. If I am correct the Pac Brake may be sticking closed but I think it may be a bad solenoid which applies air to the Pac Brake, and when you turn off the Pac Brake the solenoid release the air and power returns to normal. When the Pac Brake is engaged and you attempt to apply power the engine can not open the butterfly valve closing off the exhaust and the Turbo can not produce boost so the engine will not run properly.

I would first check the Solenoid to see if it is defective or is receiving power to engage when it should not.

[Beagle RC Air]

Quote:

Originally Posted by Dave Fernandez Hello Greg: If I understand correctly, when the exhaust brake (Pac Brake) came on you lost power when you attempted to accelerate back to normal speed. If I am correct the Pac Brake may be sticking closed but I think it may be a bad solenoid which applies air to the Pac Brake, and when you turn off the Pac Brake the solenoid release the air and power returns to normal. When the Pac Brake is engaged and you attempt to apply power the engine can not open the butterfly valve closing off the exhaust and the Turbo can not produce boost so the engine will not run properly. I would first check the Solenoid to see if it is defective or is receiving power to engage when it should not.

It has been my experience that the solenoid willl fail to operate on occasion and cause this problem as Dave has described above. The failure of the solenoid to function was traced back to a defect relay. This can be easily checked out by switching out the exhaust brake relay with a known good one. I used one next to the failed relay.

[Dave & Colleen]

Where is the solenoid located? Sounds like its a good spare item to carry, with that said. Do you still have the replacement part number for the solenoid?

[RustyJC]

It sounds to me like the solenoid is working if the exhaust brake activates when you turn on the switch and deactivates when you turn off the switch. If I were troubleshooting it, I'd first look upstream in the accelerator pedal position actuation trigger circuit, whether it's coming from the ECM or a separate accelerator position switch.

If the contacts are welded in the relay mentioned above so that it's always engaged, it would cause the symptoms you seem to describe.

Rusty

[Greg from Pittsburgh]

Thank you for all the help, I will take a look at the solenoid as this seems to be the easiest and it would also help make sense of why I've never thought the exhaust brake was working. Where is this solenoid anyway?

[EngineerMike]

Greg- you'll find four PacBrake docs on the Alpine Coach Tech Library page under Chassis. One is exploded parts, one is maintenance tips. These should help you locate the PB and deal w/the parts.

[Greg from Pittsburgh]

Are we talking about a relay or a solenoid? The solenoid could most likely be found by tracing the air line coming off the Pac brake lever on the exhaust, but where in the world is the relay?

[Beagle RC Air]

The relay is in the electrical panel directly ahead of the passengers feet. It will be within one of the four 4X4 enclosed fuse covers. It is clearly marked, just carefully pull out the relay and switch with one of the other relays nearby. My problem was having the brake not to go off after use. When it stays on the exhaust smoke and lack of power will let you know it is hung up. I made sure it was free at the exhaust manifold and all the other things recommended. The problem was the relay which failed on occasion.