as the title says, my pac bake will randomly turn on and off very quickly while at idle in park or in gear. when it does turn on and off quickly it sounds terrible, almost like the engine is going to come apart. also, if i shut the brake off it no longer does this random on and off thing.
what could be causing this, a short somewhere?

 

The truck may not be warmed up quite enough or there may be an air leak.
Are you running an auto?

If need be, Email Pac and ask for advice from TK.
I have had great service from them.

 

the truck is up to temp and has plenty of air pressure. i installed an air guage to keep an eye on things. also it is an auto.
when it turns on and off it does it so quickly that it doesnt fully enguage, just enough to make some noise and quickly back off.

 

well I was going to say temp thing but you say its at operating temp. My will do the same right as it gets to 170 but then cools a tick. Call Pac they are great to deal with

 

Sounds like a faulty relay to me but that wouldn't explain the ugly engine noise?? Have you contacted Pacbrake for assistance?

 

Check the ECM pin 42 wire, it runs to the 85 pin of the Solenoid relay. You will fine the ECM is sending the ground signal the dropping and so on and so on. Try a Throttle Position Reset, if that does not cure it see dodge for a reflash, extreamly common on 2006 and 2007 trucks, very rare in the years before.

 

As said you may need a reflash,I would email or call Harold Mclean at Pac Brake (harold@pacbrake.com) or 604-882-2332.On my 06 if the brake switch is on and you give it a little throttle and then release the throttle quickly ,you will hear the exhaust valve chatter.It is very suttle though, sometimes not very noticable at all.This is a known problem,that a reflash is supposed to fix,but since I switch my brake off and on quite a bit I have never bothered to get it reflashed.Have you actually watched your exhaust valve to see if it is chattering,you may need to use a voltmeter to some checking.Terminals 85&86 of the solenoid relay would be a good starting point,with the brake sw turned on there should be approx. 12 VDC across the termanals until the engine is almost warmed up,if its not steady you either have a flaky connection or the ECM output is not staying low.If you find it easier just check your voltage at the solenoid.Sorry my drawing is not the best,I have added notes and drawn in the relay coils.

 

thanks for all the help, i still have not had time to check things out, of course it has been around 10 or so out, so that reduces my desire to go work on the truck.

 

I have noticed my brake sounds very strange when its that cold outside,I really never diagnosed what was really happening and after a little warm up it works fine.It wasnt pulsing though like yours ,it was just not actuating or a partial actuation.