Fuel pressure issues

[thatguyHoBo]

If this has a duplicate thread feel free to delete.
I drive a 91 k2500 5.7 tbi
Fuel pump is a new-ish Precision A30033 (a vortec pump and hanger capable of 60psi)
Relay is new-ish (30 amp from oreilly - the Grey one)
Fuse looks good (yellow 20 amp iirc)
Oil pressure sender is new (just did intake manifold and replaced while I had it out)
i do have a diy adjustable fuel pressure regualtor (oe with the metal drilled out and a slit cut in the center stud)
my issue is recently I have had bogging and stalling akin to losing fuel pressure. With a gauge on my inline adapter behind the tbi I'm only getting 8-10 psi.
I checked voltage on the orange wire at the relay, it's getting 12.5+ volts while truck is off.
I checked the the purple wire at the pump harness while truck is on, 14 volts, seems high but truck was running.
Jumped terminal g on the aldl with 12v and the fuel pump kicked on. I tested fuel pressure at the same spot behind tbi while jumping terminal g, 10 psi.
Only other thing I replaced recently is the fuel pressure regulator diaphragm but you'd think if that was bad it would leak?

My thoughts are fuel pump going out, second thoughts?

My other question is am I killing the vortec pump running it in a mostly stock (for now) tbi?
I got the truck with a big ol aftermarket aluminum fuel tank and it had evap issues. Replaced with a stock tank and while I had it out upgraded the pump for plans on heads, cam, etc. Was I premature in that and limiting it to 13-15 psi is killing it?

 

[PlayingWithTBI]

With a gauge on my inline adapter behind the tbi I'm only getting 8-10 psi.

That's too low, you need 11 - 14 minimum on a stock engine.

My thoughts are fuel pump going out, second thoughts?

Probably not, you may need a replacement FPR spring.

My other question is am I killing the vortec pump running it in a mostly stock (for now) tbi?

Nope, a lot of us run the Vortec pump from a 96+

Was I premature in that and limiting it to 13-15 psi is killing it?

Nah, like I said above, you need good pressure, as an example, I'm running mine @20 PSI

 

[thatguyHoBo]

Probably not, you may need a replacement FPR spring.

Had my girlfriend watch the fuel pressure gauge while I pinched the return line. Fuel pressure shot to over 80 on the gauge. Then settled out somewhere a little over 20 psi, while no longer pinching the hose. You may be correct.

 

[Schurkey]

Running the Vortec pump at TBI pressure makes life very EASY on the Vortec pump. The thing is loafing along.

The diaphragm does not control fuel pressure provided it's not leaking. The SPRING acting on the diaphragm controls pressure.

 

[thatguyHoBo]

The diaphragm does not control fuel pressure provided it's not leaking. The SPRING acting on the diaphragm controls pressure.

I am aware of this, I only changed the diaphragm because it came in a rebuild kit, the spring unfortunately did not. I was more making the point to if it was bad and causing the lack of prssure (like a tear) it would be leaking so it would be noticeable, like you said.
After PlayingwithTBI's comment about my fpr spring I pinched the return line near the pump and pressure shot up, dropped then steadied around 20 psi. To me that says he was more than likely right about the spring.
What confuses me is with everything tested previously fuel pressure was never anywhere close to 20psi. Is it normal for the higher psi to stay constant after releasing the pinched line? Or should it have fallen back to the previously mentioned 8-10 psi once released.

 

[Schurkey]

Fuel pressure should return to what it was after the return plumbing isn't restricted any more.

If it didn't, either the return plumbing was still partially-restricted, the regulator got a "tune-up", maybe blowing a bit of debris off the seat, or the gauge is inaccurate--not repeatable.

 

[thatguyHoBo]

If it didn't, either the return plumbing was still partially-restricted, the regulator got a "tune-up", maybe blowing a bit of debris off the seat, or the gauge is inaccurate--not repeatable

Re checked fuel pressure this morning, same result. 8ish psi. Pulled regulator apart and spring is intact at least. Cranked afpr spring all the way up and I am only getting 11 psi.
Will more than likely order a new fpr kit with spring and rebuild and recheck. Might try to install the stock fpr to see if it has an affect.

 

[Schurkey]

Are you using a 100-psi guage and trying to get accurate results at ~10 psi?

If so, you might want to get a quality, NON-liquid-filled 0--30 psi gauge and install it on your fuel pressure testing hose. If your gauge is liquid-filled, you have to burp it at the rubber plug before EACH use.

 

[thatguyHoBo]

Are you using a 100-psi guage and trying to get accurate results at ~10 psi?

Unfortunately, yes, as it is what I have. It's a Pitsburgh (harbor frieght) non liquid filled. It's an older version without the pressure relief near the gauge. Came out of one of their generic fuel pressure test kits a while back.

I'll look into something to get more accurate readings.

I threw the non adjustable stock fpr housing back on and got the same approx 8 psi.