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Discussion Starter #1
Lot's of threads about fuel lately. Here's my question:

Fuel pressure normally runs ~ 70 psi in idle after the "blue spring" mod and drops to 55-60 psi at heavy load. Truck "seems" to run fine. But a recent change is ~47 psi in idle, and drops depending on load, even down to 30 psi. :(

1) Fuel pressure gauge might be faulty (I'm trying to verify this).
2) Don't think it's clogged filters because the pressure is still low at idle.
3) How do the OEM pumps fail? Suddenly dead? Or is there a graceful degradation?
4) The fuel pressure regulator ("blue spring") gone bad? How could I test for this?
5) Fuel filter flow-by pressure leakage?

Other ideas? Troubleshooting ideas?

Thanks for the suggestions!
 

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All great questions and possibilities.......

Harry
 

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Mine reads 72-75psi and drops 5psi under load. Cold weather when fuel thickens can make it go up to near 80psi. That said, if this was a sudden change in fuel pressures, I would change the filters first, if still no change for the better, then I would take the pressure sender for the gauge out of the secondary filter test port and hook up an actual mechanical fuel pressure gauge and see what I have, this will tell you if your pump is weak or you have some type of flow restriction or bleed off-suction issue such as a crack in the tank pickup line.

But since I'm way late to respond to this, I'm thinkin you have probably figured this issue out already.

Harry
 

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Discussion Starter #4
All great questions and possibilities.......

Harry
With truck age and milage, I decided to replace fuel pump. Preventative maintenance either way. What a PITA that was in my garage with a crawler. Anyway, that wasn't the problem.

Turned out the fuel pressure regulator plunger gasket failed (see attached picture). Already had a new blue spring kit on order. Easy fix.
 
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Discussion Starter #6
Needed the blue spring anyway ?
Already had it. This is my second one. Can't remember how many years it lasted. But I installed it when they first came out.
 
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