Engine/Transmission (1998.5 - 2002) LP install question

[Ncostello]

Had to install a new lift pump. Had to do it in the garage and buy the pump, even though warranty would have covered it... I didn't want to hassle with towing. Long story short, I had it in Schied the day before to troubleshoot the now new crank position sensor. They were going to do a fuel pump check the next day, but I decided to change the fuel filter the night before. It wouldnt prime at all. The LP wouldn't fill the cannister after I even removed one of the brass plugs from the top aluminum housing. So I just bought and installed it myself.



Only thing was though, when I got it on, the pump only filled up the cannister after totally removing the brass plug completely. When I took it off, the pump finally sounded like it was under load and the tone got louder like it was pumping liquid and not air (Free spinning). I suppose this is how it works. But I figured once all the air was out it would sound like it was under load and pumping fuel... back to the tank and all.



Well, I cranked the truck for about 5-7 seconds and it started, and ran fine without a flutter which is light years ahead of where I was yesterday.



My question is, once the system is completely purged of air, should the pump sound "loud" or loaded constantly when I bump the key and let it run for 30 sec. Right now, when I bump the starter, the pump just sounds like a little quiet electric motor, without that loud humming I got when it finally picked up fuel. It sounds just like my "dead" one did when it would not prime the system. I am worried I got a new unit that is also bad. Do new ones go bad right off the shelf. Scheid said it was the latest revision available. Thanks.

 

[TomGolden]

My guess would be that while the pump was running at first, with air still in the lines, it was noisier because after the lines filled up with fuel, the fuel dampens the sound of the pump motor running. Kind of like if you yell at someone, and then put your head under water and yell again... the water absorbs a lot of the sound.



Sounds like a good theory anyway



Tom

 

[Ncostello]

Thanks Tom...



I suppose I could take the old one apart to see what happened to it if anything. At least it would help me understand a little more what makes it tick... or not tick. My guess was that when purging the air it was pumping at its max volume (cause the flow sure came out that removed brass plug) and when it was full, not as much volume was being pumped or needed so it quiets down??? Maybe the whole key here is understanding precisely how it works... . which helps with how it fails.



Really though, I just need to get me a dern pressure guage. 15psi good... much less is not as good.