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P0171, P0300, P0306 Faults in 1997 Pontiac Grand Prix GTP with Supercharger: Symptoms After 15-Minute Drive Cycle

Model: 97 Pontiac Grand Prix GTP Fault Code: P0171 Posted: 2008-06-10 00:09

After purchasing the 1997 Pontiac Grand Prix GTP, I began experiencing recurring engine issues while driving home. The vehicle exhibits symptoms including loss of power, knocking, stalling, and hesitation—specifically triggered by a pattern: after running the car for at least 15 minutes, parking it, and then restarting. During the first drive of the day (morning, noon, or night), everything operates normally. However, after this rest period, the P0171 (Fuel Trim Bank 1 Too Rich), P0300 (Random/Multiple Misfires), and P0306 (Misfire Detected in Cylinder 6) codes appear. A distinct 'ticking' sound is heard near the top of the engine just before symptoms manifest. In some cases, after an initial hesitation or misfire, the engine runs smoothly again. The most puzzling incident occurred this evening: the car accelerated normally to 55 mph at a stoplight, but when I pressed the accelerator to pass another vehicle, RPMs spiked by 1500 (supercharger spooled up), yet the car failed to accelerate—appearing as if in 'suspended animation.' After stopping and restarting, normal acceleration resumed. No check engine light or codes were present at that time. I have also noticed a whistling noise from the fuel pump, which began only recently. I suspect this may be related to fuel quality or system pressure issues. Given the supercharger setup, I am concerned whether elevated boost pressures could exacerbate pre-ignition or misfiring under certain conditions. I currently use an Actron code scanner and have not yet tested fuel pressure. I'm seeking advice on how to safely check fuel pressure using a standard gauge at KOEO (Key Off Engine On) conditions, idle, and monitoring for any drop in pressure. Additionally, could EGR or exhaust backpressure contribute to P0171? Are there known issues with intake gaskets in GTP models under high boost environments? I have also considered fuel octane—since the car is equipped with a supercharger, higher octane fuel (93+ recommended) is critical. I suspect that during my initial fill-up, I may have received 87-octane fuel from a pump labeled as 93. This could lead to pre-ignition and misfires, especially after the engine has warmed up. Could this explain the pattern of symptoms occurring only after extended driving? After testing with Champion Octane Booster (15-point octane increase), I added two containers of booster to my tank along with 6 gallons of regular fuel and 5 gallons of 93-octane fuel. The car now runs smoothly, with only a brief hesitation upon startup. This suggests that fuel quality may be the root cause of the P0171 and misfire symptoms.

Related fault codes
P0171P0300P0306
Comments (5)
Anonymous 2008-06-10 05:03

Could exhaust backpressure be contributing to the P0171 code? Specifically, is it a restriction in the exhaust system such as a clogged catalytic converter or muffler?

Anonymous 2008-06-10 05:18

I suspect 'backpressure' refers to fuel system pressure. I haven't tested fuel pressure yet—this whistling noise started just last night, and the P0171 codes began two days ago. I plan to check fuel pressure today using a quality fuel pressure gauge connected to the Schrader valve. I'll test at KOEO, idle conditions, and monitor for any pressure drop. Could EGR or other systems contribute to P0171? With only an Actron scanner, I don't have full system diagnostics. What's the safest way to check fuel pressure?

Anonymous 2008-06-10 07:39

Exhaust backpressure is a common cause of P0171—check the entire exhaust system for blockages, especially catalytic converters or mufflers. First step: use a vacuum gauge to assess intake manifold pressure. For fuel pressure testing: connect a reliable fuel pressure gauge to the Schrader valve (typically located on the fuel rail). Test at KOEO (Key Off Engine On), idle conditions, and monitor for any drop in pressure. Compare readings against OEM specifications. A consistent bleed-off or low reading may indicate fuel pump or line issues. Good luck—please update us on your findings.

Anonymous 2008-06-10 21:19

I'm now considering that the misfiring and sensor-related delays occur after initial sensor timeouts (15–30 seconds). I've owned both a 1999 and a 2002 Grand Prix, and never experienced this issue. This suggests it may be linked to fuel quality. Given the supercharger setup, lower octane fuels can cause pre-ignition—especially under high boost conditions. I suspect that during my initial fill-up, I received 87-octane fuel from a pump labeled as 93. When the engine warms up and runs for over 15 minutes, this low octane could trigger misfires and P0171 symptoms. This timing aligns with the pattern of symptoms appearing only after extended driving. Is this a plausible explanation?

Anonymous 2008-06-11 00:24

After careful testing: I added two containers of Champion Octane Booster (15-point increase, 1.5 octane per 21 gallons) to my tank, mixed with the remaining 6 gallons of regular fuel and 5 gallons of 93-octane fuel. The car now runs like new—only a brief hesitation at startup, then smooth performance. This incident occurred after I filled up from a pump labeled as 93 but likely contained only 87 octane. Five days later, another fuel truck driver accidentally put the wrong octane in the station tank. I’m grateful for the experience—it’s been a stressful five days of troubleshooting and sleepless nights. To that driver: THANK YOU FOR NOTHING! This confirms that fuel quality is critical for supercharged engines like the 1997 Grand Prix GTP.