How to tell if compressor is bad

That particular compressor has had a lot of failures and short life span. I have changed a lot of them at less than 100,000 mi. The failure seems to be in the head assembly. They still pump just slowly.

 

Thats the unloader valve, I would get an unloader kit and give it a try. You don't have to time the fuel pump on that engine.

 

Compressors aren't made to pump liquid their positive displacement, very good chance of breaking valves or worse.

 

You need a wrench like this: http://www.apexinds.com/tools/M20156.html I heated and bent up an older wrench. Is the flange that you're talking about the accessory drive? That wont come off unless you take the accessory drive pulley off.

 

Replace the plastic cog air compressor to fuel pump. Maybe also check all air lines for carbon build up

 

that's a lot of quarts

 

How can check if my air compressor is bad before taking it off/replacing it on a 2006 peterbilt 387

 

A compressor is something that will give you air 24/7 at any situation idle to cruise and beyond. If you do not get that air you need when the truck is in, then that thing needs to be looked at.

I had a compressor fail quietly at dinner near Doswell one night, came back to a completely locked rig and a cold outbound air line to the tanks from the compressor. The resulting fiasco is already told in previous posts. It is rare that they break.