I'm new to my '05 3500. My old '93 had a manual priming lever on the lift pump and you had to open a bleeder to purge the air. The '05 says to bump the starter to trigger the fuel pump to prime for 25 seconds. Where does the air go? Back to the tank? Is air in the line less an issue with the 3rd gens?

Rocky

 

Yes the air goes back to tank.

 

Unlike your 93 Cummins the 05 diesel is a common rail diesel, the rail is always under high pressure diesel fuel when running or when cranking the engine over. You should never open any fuel lines on a running common rail diesel. If you do the injection pump will go max pressure and could inject high pressure diesel fuel into your skin. If diesel fuel enters your blood stream it could cause death in seconds. Just a word to the wise.

 

The old mechanically injected engines used fuel pressure alone to open the injectors. When there was air in the lines, the injection pump would not be able to build pressure in the lines to open the injectors because the air would compress, unlike a liquid.

The common rail engines use the ECM to open the injectors electrically just like a gasoline engine, so regardless of how much air is in the line, the injector can still open and push out all the air.

 

When you turn on the ignition key if listening closely you can hear the #1 injector firing to purge the air.

MikeyB

 

Thanks everyone. I did not realize the injectors were electrically opened. Likewise the word to the wise on the diesel pressure. A flu vaccine is ok with me, but a diesel shot is not.
Now that I understand the purging, I will change my fuel filter next weekend as long as the weather holds.

Rocky