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1996 Chevrolet Suburban P0300 Code: Fuel Pressure Regulator Issues and Engine Starting Problems

Model: 96 suburban Fault Code: P0300 Posted: 2007-12-14 19:58

Four months ago, my 1996 Chevrolet Suburban with a 5.7L Vortec engine began throwing a P0300 random misfire code. The dealer replaced the fuel pressure regulator at that time. Less than 500 miles later, I'm experiencing repeated starting issues—when cranking, the engine seems to backfire or fail to release pressure, resulting in low crank speeds and failure to start. Occasionally, after a 10-20 second delay, it will 'catch' and start; other times, it fails to start even after multiple attempts. While driving, I notice intermittent hiccups at light throttle, which suggests fuel delivery or combustion inconsistencies. The only stored diagnostic trouble code (DTC) is P0300. Using AutoEnginuity software, I've reviewed the fuel trims but am unsure how to interpret them for diagnosing potential issues with the fuel pressure regulator. I currently do not have a fuel pressure gauge, and local auto parts stores are out of stock. Can fuel trim data help identify problems related to the fuel pressure regulator? Is there a correlation between abnormal fuel trims and inconsistent fuel pressure during cranking?

Related fault codes
P0300
Comments (7)
Anonymous 2007-12-15 09:35

When was the last time a tune-up was performed? Can you share your fuel trim readings? This data can help identify misfire sources or fuel delivery inconsistencies.

Anonymous 2007-12-16 16:00

It's cold outside and the truck is now having trouble turning over. I don't have access to fuel trim data—can anyone recommend a beginner-friendly guide for diagnosing these issues? The symptoms sound similar to an older engine with improperly timed distributor operation, where spark timing doesn't align with valve train movement.

Anonymous 2007-12-16 16:58

Is the battery in good condition? Are terminals clean and securely connected? Is the vehicle consistently turning over slowly before starting? Is fuel reaching the engine? A fuel pressure gauge is essential for accurate diagnosis—consider getting one from a trusted auto parts supplier or mechanic.

Anonymous 2007-12-19 13:17

This is extremely frustrating—the truck has not started at all. I replaced the crankshaft position sensor, but no start occurred; backfiring decreased slightly but didn't resolve the issue. Fuel pressure was measured at 55–60 psi. Leakdown test showed low values (possibly around 5 psi over 20 minutes), though it wasn’t specifically measured. Spark and AFM readings appeared normal—cleaned with fuel system cleaner as a trial. I reseated the fuel injector spider connector, but still no start. To confirm if fuel was actually flowing during cranking, I started with 58 psi in the fuel line, unplugged the fuel pump relay, then cranked. After 3–4 seconds, pressure steadily dropped from 58 to 40 psi and the engine kicked over—but died immediately. When I reconnected the relay, it started right away. Multiple start-stop cycles have since allowed normal operation. This behavior is highly unusual—why would fuel flow only when the relay was disconnected? My scanner now won’t connect to the vehicle. When viewing DTCs, which pin measures V+ (positive voltage)?

Anonymous 2007-12-19 13:21

I meant DLC (Data Link Connector), not DTC.

Anonymous 2007-12-19 13:25

Check the fuses—especially the cigarette lighter fuse—which can affect fuel pump operation and power delivery to the engine control module.

Anonymous 2007-12-19 17:54

For future reference, my truck’s issue was resolved by simply reseating the fuel pump relay in the under-hood relay box. I remain puzzled as to why the fuel pressure measured at the Schrader valve was in the upper 50s during normal operation. After the engine started again, I noticed slight fluctuations in fuel line pressure (approximately ±1 psi). Previously, when starting, the pressure remained stable—completely unchanged during cranking or after ignition. Does the fuel injection system have a maximum operating pressure? Is there a limit on line pressure? Does the fuel pressure regulator regulate this maximum and return excess fuel to the tank?