No pressure after fuel pump replacement???

core-rider

core-rider

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I removed the front tank, verified no leaks on capped lines, and built fuel pressure on the stock rear pump. I then replaced the rear pump with a Quantum 340lph unit. The pump cycles, but I cannot build pressure. I thought at first it was not picking up because fuel level was so low, but I've put about 7 gallons in now, gauge reads over 1/3 level and still can't build pressure. I tried jumping out the fuel pump relay just to let the pump run with no change. Almost like the pump is airlocked and won't prime.

Am I missing something here?
 
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core-rider said:
I removed the front tank, verified no leaks on capped lines, and built fuel pressure on the stock rear pump. I then replaced the rear pump with a Quantum 340lph unit. The pump cycles, but I cannot build pressure. I thought at first it was not picking up because fuel level was so low, but I've put about 7 gallons in now, gauge reads over 1/3 level and still can't build pressure. I tried jumping out the fuel pump relay just to let the pump run with no change. Almost like the pump is airlocked and won't prime.

Am I missing something here?
Click to expand...

Yep, been there, done that. Unless something changed, when I got mine from Quantum, it’s missing the plastic spacer that goes under the gasket that the snout of the fuel pump fits in on the canister. You will have to remove it from your old one and install. Check out the pics below. That pump falls down into the bottom of the canister and the fuel escapes around it. When you put the spacer in, it will be a tighter fit and not allow this to happen.
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Here is the spacer. I pulled this from an old pic Steve83 posted a while back. The gasket and spacer are in the blue circle. Spacer is in the res circle.
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That’s what I used too. That’s what I was saying. They don’t instal the spacer.


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Oh okay… we’ll crap guess I’m dropping the tank again.


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ASAP said:
That’s what I used too. That’s what I was saying. They don’t instal the spacer.


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Click to expand...
Same here, except I added to what was already there because the stock grommet wasn't enough.
 
core-rider said:
Oh okay… we’ll crap guess I’m dropping the tank again.


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Click to expand...

Exactly the way I felt. And should have mentioned that the grommet that the pump goes into comes out of the canister hole too.


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Blurry94 said:
Same here, except I added to what was already there because the stock grommet wasn't enough.
Click to expand...

I think it was you that pointed me into that direction when I had the problem. I think we covered it in my 772 upgrade post


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I bought quantum 255lph fuel pumps (front and rear) and just replaced them. I wondered why they give zero install instructions with the pumps, I thought it was strange. Now reading this makes it worse, I dropped the rear with the bed on and I'd be livid if I had to do that job again because of their lack of instruction
 
Yea that’s how I did it too.. 3 times to get it right. Actually got it down to about 30 min removal the last time and that’s without a lift.


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ASAP said:
Yea that’s how I did it too.. 3 times to get it right. Actually got it down to about 30 min removal the last time and that’s without a lift.


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Click to expand...
I jumped the fuel pump relay so I could drain some of the gas out and there was no pressure... it was basically just dribbling fuel out. It also sounded like I could hear fuel falling in the tank like there was a leak.

So I've got the tank down, pump assembly out, and sure enough it's missing the spacer. The hole in the spacer is about 0.010" smaller than the pump so I drilled it out and the very tang end of the spacer had to be cut off because there's not a spot in the pump to accept it like on the stock pump. The grommet fits nice and snug into the pump housing and on the pump. I'm skeptical putting this all back together just to potentially find out it's still not right. :cautious: I guess there's no way to find out but to do it though! Quantum is closed till next week so I can't even get their opinion on it. They will for sure hear from me next week though!
 
Well that did it… first key turn and 42psi. Now I’m wrestling the filler hose back onto the tank.

Edit: All done finally and truck starts right up showing 42psi. For people wondering in the future… this is the part missing from the Quantum assembly. It has to be removed from the stock assembly. I had to slightly drill out the hole in the center to fit the new pump and trim off the end as seen in pics because there wasn’t space for it on the Quantum pump.

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Sweet! Glad you got it man! Yea I meant to follow up with them too, but honestly forgot all about it.


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is that QFS 340LPH still good to go? Ordered one and will be installing it soon, I guess doesn’t hurt to check it before I drop it in.
 
Been good since I installed the spacer. I explained to them the issue, sent an email with pics but never heard back so I don’t know if they have fixed their packages or not. Good luck with it!


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I think they changed the design of this.. the pump now has a metal tip on it. It looks different than the pic in post #13. Maybe it has more of a “bump” but it seems to fit very tight in the grommet. So much so that I struggled to pull it out. I decided to run them as is and see how it works. Both pumps make 40 psi but I’ll keep a close eye on them.
 
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