Advice requested

[Stubbornbastard]

My '04 Chevy Tahoe (Z71 if it matters) with a 5.3 lit up my check engine light. Had the big box retailer read the codes and got P0300, needs a new fuel pressure regulator. Bought and installed one, now it runs worse. I had disconnected the battery to clear the codes. The check engine light popped back on, had it read...P0300, needs new fuel pressure regulator. Any suggestions of what I could look at next or should I just throw my hands up and take it to a shop?

 

[Fless]

P0300 doesn't indicate anything specific to the fuel pressure regulator; it indicates a random misfire. See the diagnostic path at the link below, but verify your vehicle info first and navigate to the appropriate code's diag procedure.

Powertrain Controls Diagnosis — 2004 Chevrolet Tahoe 2WD V8-5.3L VIN T Service Manual | Operation CHARM

Detailed repair manual for the 2004 Chevrolet Tahoe 2WD V8-5.3L VIN T.

charm.li

Note that a CASE relearn (as indicated in Step 2) should be done prior to proceeding with the diag. A CASE relearn is recommended when either the crank or cam sensor (or both) is changed. Best results with replacements have been using GM OE or AC Delco sensors, when they're needed.

I'm curious, what's the running fuel pressure at idle, using a fuel pressure gauge on the passenger fuel rail schrader valve?

 

[OR VietVet]

Welcome to the forum from Oregon.

As @Fless said, P0300 is for random misfires. How the person came to a realization that P0300 means you need a fuel pressure regulator, is beyond me. The code does not tell you what you need, it tells you the system that is throwing codes and needs to be diagnosed instead of firing the parts cannon and throwing parts at something with your fingers crossed. The "big box retailers" read codes for free so you will listen to the unqualified and buy parts from them. Once it is installed, you cannot return.

By the way, Z71 matters in my book.

 

[Scottydoggs]

your reading that code wrong like stated, you either need a tune up super bad or the cats are clogged up. really the only things that set that code, other then maybe you installed a new large cam and didnt get a tune.

when you floor it wot if the cel flashes, thats the cats for sure.

 

[Marky Dissod]

My '04 Chevy Tahoe (Z71 if it matters) with a 5.3L ... lit up my check engine light ... P0300, needs a new fuel pressure regulator. Bought and installed one, now it runs worse ...
check engine light ... P0300, needs new fuel pressure regulator. Any suggestions of what I could look at next or should I just throw my hands up and take it to a shop?

Before you throw up your hands: LM7 or L59? They use different fuel pressure regulators. Once you're sure you installed the right one, THEN
then take it to the nearest TYF member with P0300 experience, or the nearest TYF-recommended shop.