nbone28

I’ve got a 2015 Mack Pinnacle CXU613 with the MP8 in it. The previous owner had the truck deleted when he first purchased the vehicle. I am not sure how they deleted the DEF system but it does look like the one box had been cut open and welded back closed. There is a CEL on, everything is related to the DEF system. The regen light has recently been coming on and off while driving and the exhaust temp gauge has been running high, not sure if there’s a correlation there. The problem I’m having is when under load and even empty just pulling a flatbed the truck feels like it hits a wall when getting on the highway and doesn’t want to pick up speed. I’ll be in 7th gear and I’ll get up to 40/45 and it feels like it doesn’t want to go. It takes a while to get up to 65 and if I have to climb a hill forget it I’m dropping down to 35/40, even empty I’ll drop down to 55. I just had the gaskets on the exhaust manifold, the turbo, and the egr all replaced along with new piping from the turbo back to the one box. No leaks. I’ve talked with a mechanic he believes it could be something with the program they put in when deleted the truck and or the truck needs a valve adjustment. Any insight would be much appreciated. Thanks

UPDATE: Replaced the maxi valve, no more air pissing out of that yellow air exhaust line underneath the hood when you go to push in the trailer air supply. Replaced the spring brake valve on the trailer, brakes are applied within milliseconds of pulling the red button out. No air pissing out of that yellow air exhaust line when pulling the red button out either. PSI holding at 120 when you go to pull the button to set the brakes and not dropping to 80psi like before. Thank you all for the helpful information throughout this process. It is much appreciated. Thank you.

With the hole in the web & that it wasn’t rising to system pressure. the flow out of the red & blue lines were good.

Bought new spring brake valve from results of the test. Should be here Tuesday. Let’s hope this solves my issue.

I will give this a test, thank you

Are there signs to look for that would indicate that spring brake valve to be going bad? How would I go about determining the lines have “crap” in them?

Where’s the SR-5 located at on the trailer?

I just timed it, it was 43 seconds from initial pull on the trailer brake to the first venting from the trailer and then 26 secs to the second venting after the first venting.

Thanks for all the information and help, it’s been a bit confusing on my end with initial information but I appreciate sticking around and helping me out with this. Thanks again

no they were all set properly

So we’re good then? That air coming out of the air exhaust line is fine? When I pull the red button the air pressure is staying at 120psi, no initial drop in psi. Dropping to 90psi when I go to push the button in, but no air is coming out of that air exhaust line.

I also just went and adjusted all the brakes on the trailer just to be certain

Yes trailer has air suspension

Yes that was the initial problem. I did not know that that air exhaust pushing out air when you pull the red button out is not bad. So with tanks full at 130psi (when the air dryer blows) I push in the trailer air supply button and it drops to 90 psi and then will build back up. (no air is coming out of that air exhaust line) With tanks full again, I pull the button out and the air pressure slightly drops, but there is air coming out of that yellow air exhaust line. About 1-1.5 mins after pulling the button out i get that air exhausting from the trailer twice, first one and then probably 30 secs after a second woosh of air.

so that line is supposed to be blowing air out it when i pull the red button out?

Yes i’m getting that blast of air exhausting from the trailer probably about a minute id say after setting the trailer brakes

Got the new brake can installed, I’m still getting air pissing out of that yellow airline underneath the hood when I go to pull out the red trailer air supply button, this time it’s dropping to 110psi not to 80psi like it was before. Still trying to figure out what’s going on.

It did come apart when i removed it but okay. Got the new maxi valve in was able to finally get the trailer air supply knob to stay pushed in, have something holding down that trolley brake, and found an brake can leaking on the last rear axle.

I had said that in the beginning, I said it needed to be changed out regardless. I have a buddy helping me out over the phone but he’s at a loss on what it could be also. At this point might have to find a mobile mechanic who can come out and take a look. Clearly I can’t get the trailer to move at all.

That was the old one. That middle part fell out when I took it out.

It won’t stay pushed in, no matter how long you hold it in. I hooked the emergency line up to the airline setup i have to air up the tires and it still won’t stay pushed in.

taking the new valve back, claim it’s faulty and swap it out

yes this is the new valve assemble, lines are off button still won’t stay pushed in, the supply for the truck goes in and stays in perfectly fine. it’s the trailer one that won’t. No the lines aren’t crossed.