Fuel Delivery Question

Chasing down the PO171 code and after eliminating (IMO) other possible causes, I've narrowed it down to fuel delivery.

The fuel pressure is around 24 PSI and does not increase or decrease with add RPM's.
Long Term fuel trims on both banks is 19.5%
Short term on both banks are below 1%
Also, when I "stomp" on the pedal the truck falls flat, but can slowly bring up the RPM's.

Before I have the pleasure of dropping the tank and at almost 70, I'd rather not.
My question is, does voltage to the fuel pump have anything to do with the pressure?
If so, is there a way to check and if so, what numbers should I be looking for?

TIA

 

A constant 43psi is what you want. That is looking like a bad pump to me which corresponds with your LT fuel trims trying to add lots of fuel to maintain AFR.

 

Voltage at the pump certainly can affect pressure.

Does it happen often? No. Have I seen it? Yes.

There's not really a good way to check it without either having an amp clamp and scope or getting to the pump and checking it there.

At least the pump still works so you can use it to pump the tank out.
Unhook the fuel line in the engine bay, hook a hose up, and jump out the COPN relay.

 

Yes and I've also read the pressure should be between 40.8 and 41.7.
I'd rather either of those than the pressure I'm getting now.

 

Amen to the pump still working because the check engine light came on around Kerrville on my way home with a fully loaded bed with gear pulling a trailer that was also loaded with gear. My last fill up was in San Angelo so that tank was down to just above a 1/4 when I pulled in the driveway.

@Dm93, can you give some instructions on how to jump out that relay? And, I'm assuming the relay you mentioned is the redish relay I pulled to relieve the fuel pressure on the lines before disconnecting them?

TIA!

Borrowed Photo from another TW thread.

 

The Red relay is the Fuel Pump Relay, the Blue relay to the right of it is the C/OPN Relay.
If you jump Pins 3 & 5 (larger terminals) and turn the key on the fuel pump should run.

 

Pretty confident the low fuel pressure issue with my truck has been corrected. Voltage to the pump seems to have been the culprit. Three years ago this month I installed a fuel pump kill switch. Today I bypassed the wiring to that switch and was happy to see the pressure where it should be and was "fricken" ecstatic knowing I don't have to drop the tank.

Total spent was about $43.00 for a fuel pressure test kit and the quick disconnect adapters. Time, doesn't matter. I'm retired and have all the time I need. Besides, it was also a great learning experience.



Thanks to all and to quote @Dm93 "Test Don't Guess."

 

Nice, sure beats dropping the tank.