First of all I am new to Diesels. I am getting near the end of doing an Oil cooler, EGR delete, Blue Spring, Stand pipes, and dummy plugs on my 2005. I have everything back together and read somewhere to cycle the key on and off 3 times before trying to start. When i do that I hear a hissing noise that sounds likes its coming from the fuel bowl. .

Its not real loud but it is noticeable. I have no idea if that noise was there before or not. I am acutely aware of anything leaking, weird noise anything after doing this major job over the course of a few days. After a few seconds the fuel pump shuts off and the hissing noise fades away. I assume that means what ever pressure or check its looking for is reached. I don't see any leaks anywhere. Is this just fuel running through the system? I haven't tried to start the truck yet. Thought i would what to hear from the experts about this noise.

Thanks!

 

You should be fine, you are just hearing the fuel pump pushing the air out of the system. I just did the blue spring in a friend of mines truck and happened to be near the engine when he keyed the ignition to the on position and I could hear it pushing the air out of the system and then I could hear it bypassing fuel once it got the air out.

 

Have someone else fire it up while you watch for leaks. Don't forget your safety glasses

 

I had my fuel pressure gauge when I did mine, it took more than 3 key cycles to purge all the air, when the gauge started to register proper pressure you could hear the sound change at the same time. I think I could go just by the sound now, just wait till you hear the sound change and it should be purged. It will also take a lot of cranking to fill the Hpop reservior with oil.don't get scared just keep cranking under 30 sec intervals at a time until it fires .

 

Yup, nothing to worry about. They usually make some strange noises when the air is being purged.