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Discussion Starter #1
I have bought a Fass 165 Titanium Signature series pump that came off a duramax. Bought the correct fittings to hook it up to my truck and also installed a sump. Pump flows good into a bucket, getting good fuel flow without air and such. But when I hooked up a electronic pressure gauge through my Edge CTS2 it shows only 8 PSI at idle. My question is can I adjust the fuel pressure by getting just a new spring for the return line to increase pressure? Or is there a new assembly I should be buying?
 

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Try stretching out the spring. I had the same issue. Stretching the spring took some trial and error, but it worked.


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Check ball.

I’ve also heard of people replacing the FASS spring and ball with the Air Dog one.....but I haven’t looked into it nor tried it.


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Just stretch the spring a bit. I had to that for my 99’ CTD, I got it to be consistent at 16psi at idle.
 

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Discussion Starter #6
Check ball.

I’ve also heard of people replacing the FASS spring and ball with the Air Dog one.....but I haven’t looked into it nor tried it.


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Thats what I thought. The duramaxs must require a lower psi to have a diaphragm infront of instead of a check ball. Have to look at buying that assembly.
 

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Cummins only requires 9-10 psi at Idle and only 3 psi or more at WOT, unless you are highly modded.
 

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Yeah, could be so, but the numbers I posted are for 3rd Gen.
 

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My 05 has a healthy pump and idles at 8-9psi, it can drop to 1psi at wot.
 

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I have a 2005, I run at about 16psi at idle. Can’t hurt can it?


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Pdd did a whole series on fuel pressures. You should check it out.

I’m fairly certain that you’re safe running 16psi.
 

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15psi is the default FASS setup for the common rail cummins, but it's overkill like mentioned for most trucks.
 

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Oh wow mine fluctuates between 18&22. Should I be concerned? Where do I adjust it down?

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There is a chance it elevates or cause eratic RP but usually at much higher 30 +psi

Like any pump, the fuel pump runs under more load so heats everything up, wears everything out faster, no need for more then 11 psi at idle.
With high ambient temps, low fuel level can heat fuel cause issue as fuel does help cool/lube system components.
 

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Discussion Starter #17
What I ended up doing was exactly as mentioned above, stretched the spring longer until I found the pressure range I wanted. Now at idle I get 16-20 psi depending on how cold the weather is outside. Hasn't skipped a beat yet!
 
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