Engine/Transmission (1998.5 - 2002) PacBrake problem...not the usual symptoms

[dmurdock]

I have a strange problem with my pacbrake (don't think I've ever seen this posted before). I have it installed using the pin on the ecm to act as the throttle switch. Now, for some reason, when i activate the in-cab switch, the brake engages, and when I turn it off, the brake dis-engages, regardless of throttle position. I've heard of the underhood vacuum valve becoming clogged, but my valve works fine, the ecm controlled throttle switch seems to be DOA.



any ideas??

 

[dmurdock]

I took the relay out, sprayed it with cleaner, re-installed it and everything works... . maybe some moisture got in there or something, who knows... .

 

[FDziurda]

Vacuum Solenoid

I've mounted my solenoid next to the driver's side hood hinge and have had to disassemble and clean the vacuum soleoid numerous times. Because of the relocation, the solenoid has been more susceptible to getting water into it. I finally adapted a small pill bottle, with some tiny holes facing downwards, to cover the breather filter on the solenoid. It seems to keep water from getting into the solenoid.



The last time I cleaned the solenoid, I coated the piston and barrel with a light coating of Marvel Mystery Oil and have not had any probelms since.



Good Luck,



Frank

 

[jlccc]

Originally posted by dmurdock

I have a strange problem with my pacbrake (don't think I've ever seen this posted before). I have it installed using the pin on the ecm to act as the throttle switch. Now, for some reason, when i activate the in-cab switch, the brake engages, and when I turn it off, the brake dis-engages, regardless of throttle position. I've heard of the underhood vacuum valve becoming clogged, but my valve works fine, the ecm controlled throttle switch seems to be DOA.



any ideas??

Cut the wire--you can splice it later--which goes into pin 20 of the ECM. With your engine running and transmission in PARK or NEU use a voltage meter to verify that pin 20 of the ECM goes to 0. 2V or less with the throttle pressed slightly (engine rpms of 1500 or so). When the throttle is returned to idle the voltage should go up to 13+ V within 1-2 seconds.



This will rule out any problem with the ECM. From there, it's likely either a solenoid or wiring problem. Feel free to email me if you want to discuss further.