Air Pressure Drops When Ignition OFF

Is it the truck or the trailer sometimes shonky brake lines on trailers will lose air and so the truck gauge will go down of course as its the air supplier and then you end up spending 15 minutes building the air pressure back up, when you unhook your trailer and park up your truck check and see if the air pressure is still dropping if not then you'll know it was the trailer.

 

Air start trucks were mainly used in the old line haul fleets of the big carriers like ,CF,PIE,etc.,for weight saving in the 73,280 days.You only had to run one set of batteries for the lights,and the air starter itself,weighs a fraction of what a 24 volt electric starter and related cables,wiring weighs.
Guys would take the mufflers off an air starter,and you would literally jump out of your shoes if a driver started one as you were walking by the truck.Unbelievable loud noise if you're not expecting it.I think those guys would wait till some unexpecting driver would walk by,and do it on purpose,just to see peoples reactions,would definitely wake you up!

 

When I was about 20, I walked in front of a truck that did exactly that. And yes I did jump !

 

Exactly. Every time the forklift drives into the trailer, it adds weight and the leveling valve pumps air into the bags. Every time the forklift drives out, it removes weight and the leveling valve releases air from the bags. The buzzer SHOULD sound anytime the key is "on" and pressure is below 80. I don't see anything abnormal about the OP's situation as described.

 

If its leaking that fast you should be able to hear it.

 

Good point. Didn't even think of that.

 

I have a 2008 ProStar, been chasing leaks on that POS for years. I have found two to date. Gone through multiple spray bottles, in various shops that you could hear a pin drop in (middle of the night) and no luck. if you find yours, let me know. There is a dye you can enter into the air system, just a drop or two, that you can find with a black light, that would be my next step.

When at the dock, losing air like that is normal, as was stated above. How now, that is another issue.

 

I had a air start freightliner COE, a 83 model with DM Bowman in Frederick, I think that was one of the last ones I had in normal CDL Service for wages outside of the auction house. Unplug the engine block 30 degrees below zero 3 inches of ice and snow mix on the ground 40 mph wind in a proper noreaster that has raged all weekend. 2 am monday morning.

Climb into it, shut door, turn key watch volts rise to 13.9 or so Open fuel line on floor by seat wait a moment then crank.

One of the most favorite things then happened as it did every morning with that truck in about a duration of 12 seconds or so... one cylinder will cough, fire the next one would catch becoming two then three then 4 then 5 and finally the 6th.

It was not ever until all 6 were coughing before you really started to get fuel (Air breather... no computer in sight) and air coming in to where it started to make music a few moments before really firing

Usually as the last of the air tank went into the engine.

To this day as long you had battery power you had a fuel pump. Im thinking you could strip out the 6 D cell batteires out of that metal long flashlight, hard wire the fuel pump to that and crank that SOB as long you had air.

Its not so good when you had to get a blow job off another truck's glad hand after using up all the air the first go trying to kick er on a bad day. Fortunately it is due to something else that killed her, not necessarily the three things you needed to run a old music air breathing desiel. Fuel, air and compression.

Im a telling you half the heartache, codes, breaking down or over all round general piles of mechanic shop costing money on today's retail fancy computer ####e will simply disappear when they bring back air starts that breathe normally.