HELP- pac brake wont go on after injector swap

[DMorris]

Well, this truck has been eating the green out of my wallet lately ! Bad starting cost new batteries, prv, and now new injectors (thanks T&C-Todd) .

Got it fired up tonight after injector swap (more questions coming on that later). Before I pulled my old injectors I disconnected my edge juice but kept the display. What I did to disable the Edge was pulled all the connectors that interrupted between injector, map, and I believe the rail pressure connections ,along with the ground wire. But left the data link on it. This was confirmed the correct way to disable it so that I can still have the display and not have it interfere with the smarty which will be loaded after I confirm truck is squared away and running correctly with the new injectors. I did run the truck prior to doing the injector swap and all was good.

So now I have it running on new injectors (starts and runs very nice:-laf) ,

But I flip the switch to get the pac brake on- nothing happens. A little trouble shooting shows, good air pressure to tank and solenoid, but solenoid does not open to activate air cylinder on brake. Further inspection shows no power to solenoid with truck running and switch on. Switch goes to pin 39 and is a ground (white wire), black wire from switch goes to ground. I check my ground and its good. I have a tester that pierces the insulation on the wire for checking power or continuity - so I check to see if the switch is good. Heres where I start to scratch my head. I clip one end of tester to the ground-switch on-check my white wire with other end of tested=the one that pierces the insulation- yahoo, it works perfectly, but then I flip the switch off my tester shows that I am still grounded-very slightly because the tester light is just barley lit ! another words pin 39 is kinda sorta almost grounded ??? but then why are we grounding it the rest of the way, and the big one would be- then why is the brake not on all the time ? Am I confusing anyone here ? For the guy whos reading this that is not confused - please HELP me understand and fix this. We are supposed to be on the road by monday and we are stuck here trying to get this truck ready for the next couple years on the road.



a side question on the injectors, Got it running all seems great, how do you know that the tubes are all seated proper in the injectors and that everything is 100% ? Or would I know that already ?

 

[Cattechcolt]

well, in my experience, kinda grounded means bad ground, so check your connections, and do a wiggle test on all wires in your pac brake system. If that still has no effect, go back to kindergarten tactics, i. e. , start with the pack brake solenoid, good ground and ign. hot. if that works, move on to the next section of wiring, working away from the solenoid, until you find where you continuity ends. 90% of electrical problems are associated w/ a bad ground circuit. And for your connector tubes, as long as they were thoroughly cleaned and torqued properly, and it starts good, you should be fine

 

[DMorris]

I appreciate the feedback, but I think I didnt explain this well. The solenoid does have good ground, it never gets power on the hot wire-thus the problem,

All grounds are good. It seems the white wire going back to the rocker switch does have some continuity to ground even with the rocker "open". Closing the rocker should actually make it ground and then the relay should close and put power to the solenoid, I believe this is how it should work. I was wondering first if the #39 pin where the white wire goes does some have continuity to ground all the time making this normal . And really the biggest question now that I am, rethinking this is if I am grounding the white when I flip the switch then I must be looking down the wrong avenue ? Do you think there is any chance having the batteries disconnected for a day would have any effect on the ECM ? I know that seems way out there but I had to ask. Or could it be related to throttle position ? would a drive around maybe help ? I know the last three questions seem pretty dumb, but I did machine repair for 23 years and the first thing I asked the machine operator was "what was the last thing you did to this machine" , many times you could go back and save yourself some trouble shooting by working off the changes. So I needed to ask those to hep me find direction on this.

Thanks for the help,on the injecotrs- truck does start and run good, all were clean and I did torque everything to specs,so I should be safe there. (fingers crossed)

 

[AH64ID]

Double check all the things you unplugged for the Edge to make sure one wasn't a Pac connection.

 

[DMorris]

Checks out good, pac connections all in place, still miffed

 

[Prairie Dog]

Remember that all the switch does is provide a ground for the relay.
To test the relay (the one on top of the pump), remove it and momentarily connect pins 85 and 86 together on the PAC relay receptacle. If the brake engages then its relay is bad. If you need a new relay, you can get them at NAPA for $17. 50 (P/N= ECH AR201).

 

[DMorris]

actually it provides ground to the #39 pin : Correct ? Which then does what ?

If it was just grounding the relay could I not just take that ground (white wire) - straight to the relay ?



Also I can swap relays and see what happens, did I mention this whole set up is less then a month on the truck with only about 300 miles on it ? I hope the relay is not bad already, My guess is that the relay is good, but it is certainly is a good place to look.

I am still confused on the continuity to ground on my 39 pin ? Also what does the black wire that connects into the ECM do ?

I am super frustrated with the truck,pac brake, and the freaking weather-thanks to you guys the first two will get resolved-now if mother nature would get with the program maybe I would see some sunshine at the end of the tunnel.

 

[Prairie Dog]

It been a long time but if (big "if") I remember correctly, Pin 39 provides the +12v to the coil of the relay.

EDIT: Ok that was all wrong! I found my install manual ~ Pin 39 is connected to one side of the switch so it's grounded when you want to engage the brake. Pin 42 from the ECM provide +12v relay coil voltage.

I can't imagine the PAC is bad after a month either but you never know!

 

[DMorris]

It been a long time but if (big "if") I remember correctly, Pin 39 provides the +12v to the coil of the relay.



EDIT: Ok that was all wrong! I found my install manual ~ Pin 39 is connected to one side of the switch so it's grounded when you want to engage the brake. Pin 42 from the ECM provide +12v relay coil voltage.



I can't imagine the PAC is bad after a month either but you never know!

I will check to see if I am getting 12V from pin 42 wire (black I believe) when I flip the switch. If I understand this, when I flip switch , I ground pin #39 on the ECM, the ecm then applies output on pin 42 which is what close's the relay that energizes the solenoid that opens for air to the brake. So If I am not getting 12 V (+) from pin 42- sad times - where to go now.

 

[Prairie Dog]

If you don't get +12v from pin 42, then my guess would be that the ECM isn't seeing 0% throttle. Seems like there is a procedure for calibrating the APPS (or whatever they call it on your truck) by cycling the key and slowly pressing the throttle down ~ wish I could remember better.
If for some reason you can't get the ECM to behave, you can get an optional micro-switch to put on the throttle. The problem with that is you wont get the 2 second delay.

 

[AH64ID]

If you don't get +12v from pin 42, then my guess would be that the ECM isn't seeing 0% throttle. Seems like there is a procedure for calibrating the APPS (or whatever they call it on your truck) by cycling the key and slowly pressing the throttle down ~ wish I could remember better.

If for some reason you can't get the ECM to behave, you can get an optional micro-switch to put on the throttle. The problem with that is you wont get the 2 second delay.

I agree, thats the next best place to look. You can also bypass the ECM to see if it engages by placing +12V on the Pin 42 connection into the relay with the switch on.



If the ECM isn't commanding the brake on it either doesn't see the throttle it needs to, or the coolant temp is too high (or so it thinks).

 

[TCDiesel]

Dan call Me its a easy fix... After its fixed you can post the fix. .

 

[DMorris]

Actually I did get it. went back and started over with all connections and wires. Apparently someone must have tugged the black wire out of the ECM just far enough to loose a good connection, looked good but was not in far enough to work, who would be so careless ? Thanks for all the advice, without it I would still be trying to figure it out.