Need to know fuel pressure with engine running. 5.3 Flex fuel Z engine.

[Jimmy John]

Can't seem to find this spec anywhere GM's service manuel online only shows what the pressure should be with the key on and engine off "VIN Z Ethanol: 335–375 kPa (48–54 psi) " no where does it tell what a engine at idle should be producing. Here is what I currently get:

Key on pressure engine off 52 psi
Key off engine off 48 psi.
Engine running at idle 42psi
Engine acceleration jumps to 45 for a second and drops back to 42.

2004 Suburban 5.3L Z engine

 

[Jimmy John]

Found this on another site:


"Fuel pressure for 02's according to VIN:
(55-62 psi) VIN: (V, T,U)

(48-54 psi) VIN: Z

Check the pressure as soon as you turn the key to run. It may drop a little as soon as the pump shuts off. With return-style fuel systems the pressure will be 8-10 psi lower when it is running depending on your engine vacuum. If you pull the vacuum line off the fuel pressure regulator while idling you should see the pressure rise by this amount to the specified value. You may have a problem if your VIN T pressure is less than 45 psi at idle or 55 psi when not running or with the vac line off the FPR. I would check the regulator first if this is the case. Make sure there is no fuel leaking out the vac line connection on the FPR."

 

[Jimmy John]

Yesterday I was reading 42psi at idle and 50psi with vacuum hose pulled off regulator. 45psi on the interstate and almost 50psi under moderate to heavy load. Seems to be about right according to the info above.

 

[Jimmy John]

As the weather has gotten cooler the last couple of days the pressure gauge has started fluttering a lot especially when initial start up. Needle was rapidly moving from 40 to 50 psi and after a few minutes it gradually smooths out.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[01ssreda4]

That seems a little low to me.

 

[Jimmy John]

Replaced fuel filter did not change readings so far on initial start and run.

 

[retiredsparky]

Are you having a problem with the way your truck is running? Obviously you could replace the fuel pump or the regulator and bump up the fuel pressure a little, but if it runs ok under load what would that accomplish?