The plug on the bottom of the LP

S

sstockton

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What does the plug on the bottom of the factory lift pump do? I'm asking, because, in this whole processes of tearing my truck apart, my cousin pulled the lift pump off and junked it because I'm running a FASS anyways. Well, I just got everything hooked up, and the FASS doesn't come on with the key. I ran a seperate power source the power lead that plugs into the factory lift pump harness, that triggers the FASS relay, and the FASS works and so does the relay. But still it won't come on with the key or when I bump the starter. So I started looking around and found this free 2 prong pigtail and in my diagram it shows it plugged into the bottom of the factor lift pump but doesn't say what its for. Could this be the reason I'm not getting power at the other connection?

Perhaps the ECM isn't getting a signal so it doesn't send power. If this is the case, can I just run a jumper between the two wires to fool it, or do I need to add in a resistor, what voltage does the signal need to be?

Thanks, if you need me to try and explain something more clearly let me know.
Sean
 
I thought that was on the fuel filter housing, but I may very well be wrong about that.

I would also be open for other Ideas as to why the stock wiring harness isn't sending any signal.
Sean
 
The plug on the bottom of the lift pump is what powers the pump.
 
nate said:
The plug on the bottom of the lift pump is what powers the pump.
Click to expand...

Correct, the ECM sends a signal which triggers the fuel pump relay, which sends power to the stock lift pump. The power wire from the relay to the fuel pump is black with a yellow stripe. I've never seen a fass installed on a rig, let alone looked at one, but wouldn't the factory harness be used to trigger the relay for the fass? Or do they tap the fuel pump relay in the distribution box?

Don't know if this helps or not, but i'm trying to understand you problem.
 
Well there are two plugs on the lift pump. 1 of them is the power source and comes from the relay in the distribution box. This one the FASS does plug into and I've had it set up like this for 2 years without any problem. Then there is another different shaped plug, that plugs into the bottom of the stock pump, not the normal power feed. When the stock pump was removed, this plug was just left hanging. And now I'm not getting any juice from the power feed, so I'm wondering if the ECM needs both of them hooked up to register and send a signal.
SEan
 
There is only 1 plug on the stock Carter lift pump. Could you take a picture of that mystery plug?
 
Sure thing. And unfortunately I don't have the stock pump anymore to show where I think it plugs in. However In a diagram I have of the fuel filter housing, in the background it looks like there is a plug like this attached directly into the bottom of the lift pump. If not, then I just need to figure out where this plug goes and maybe that will help a bit.
Thanks,
Sean
 
your fass pump should of came with a harnass that pluged into the factory plug and ran back to the fass pump thats how mine came
 
ramtough01 said:
your fass pump should of came with a harnass that pluged into the factory plug and ran back to the fass pump thats how mine came
Click to expand...

It did, but that plug isn't getting any power. And in my poking around I found this other plug that I can't find where it goes to, and in a diagram I have it appears to connect directly to the bottom of the lift pump.
Sean
 
So, I don't have my camera with me today, but I'll get it back tonight. Here is the diagram I am talking about though. Please let me know if I'm way off base with any of this too.

In this diagram, behind the fuel filter you can see the factory lift pump. Plugged directly into the bottom of the bowl on the lift pump, there is a little 2 prong plug, this isn't the main power plug, its something different. Its narrow and a different type of connection. This is the one that I can't figure out what it is for and if it is creating my problem.
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Sean
 
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