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2001 Chevy Tahoe P0300 and P0174: Random Misfire and Bank 2 Lean Diagnosis

Model: 01 Tahoe Fault Code: P0174 Posted: 2009-09-14 10:22

Hello everyone. I'm currently troubleshooting a 2001 Chevrolet Tahoe with persistent DTCs: P0300 (random misfire) and P0174 (Bank 2 lean). The engine is a supercharged 6.0L LQ9 V8, which has performed well until recently. The issue manifests as noticeable misfiring when accelerating from half-throttle to wide-open throttle (WOT), with a distinct hesitation during light throttle applications after a stop. Bank 2 is consistently running lean while Bank 1 shows a slightly richer air-fuel ratio than normal. Prior to the fault codes, Bank 1 had an air-fuel ratio (AFR) of approximately 13:1 to 14:1 under part-throttle load. Since the problem began, Bank 2 has dropped to around 11.3:1 to 11.5:1 under the same conditions — a significant lean condition. I've already performed several diagnostics and repairs: - Checked injector and coil operation (both functional) - Replaced both oxygen sensors - Inspected catalytic converters for clogs - Conducted vacuum leak checks with no findings - Replaced intake gasket - Installed new spark plugs (NGK TR6, gap set at 0.035 inches) - Upgraded fuel filter I'm now planning to test the MAF sensor and verify fuel pressure. Beyond that, I’m out of conventional troubleshooting options. My current hypothesis is that a misfire on Bank 2 may be triggering the lean condition — but I believe isolating the root cause of the P0300 is essential before addressing the P0174 code. Any additional insights or suggestions would be greatly appreciated.

Related fault codes

P0174P0300

Comments (9)

Anonymous 2009-09-14 10:52

Could this be a fuel pressure issue specific to Bank 2, or a faulty oxygen sensor on that bank? Have you checked scan data for real-time air-fuel ratios and injector pulse widths?

Anonymous 2009-09-14 14:02

Both O2 sensors are new. The data shows Bank 2 runs lean under boost conditions, with the lean trend worsening as RPM increases — especially above 3,000 RPM. I’ve avoided applying boost since discovering this issue because boost combined with a lean condition causes engine stalling. My current theory is that a misfire on Bank 2 may be causing the P0174 code; however, I need to first isolate and resolve the root cause of the P0300 before moving forward.

Anonymous 2009-09-15 05:20

Misfires typically don’t directly cause lean codes. Many LQ9-powered Vortec engines have known issues with leaking injector nozzles or a faulty fuel pressure regulator, which can lead to inconsistent fuel delivery and misfire symptoms. Vacuum leaks from the intake gasket or coolant leaks should also be ruled out as potential contributors.

Anonymous 2009-09-15 23:51

The injectors are 42 lb Bosch units. Fuel pressure is within specification, and injector coil resistance readings fall within manufacturer tolerances. I’ve bypassed the EGR system. I recently swapped in a known-good MAF sensor from my brother’s truck. The engine was rebuilt about 3,000 miles ago with a 10.1:1 compression ratio, Lingenfelter camshaft, and running approximately 8 psi of boost. Using NGK TR6 plugs at a gap of 0.035 inches. No coolant or oil leaks, no exhaust smoke, and no foul spark plugs. I’m planning to replace the MAP sensor tomorrow and inspect for exhaust leaks in front of Bank 2’s HO2S to determine if that could be causing the lean reading.

Anonymous 2009-09-16 06:09

Have you replaced the Powertrain Control Module (PCM), or are you still using the original stock unit?

Anonymous 2009-09-16 07:19

Check the scan data to see if the PCM is increasing injector pulse width on Bank 2 and whether both banks receive equal fuel commands. If all inputs — including MAP, MAF, O2 sensors, TPS — are within normal ranges, the issue may lie in how the PCM manages fuel delivery.

Anonymous 2009-09-16 11:07

The PCM is the original stock unit but custom-tuned for this engine setup using EFI Live software by a professional tuner. All injector duty cycles and pulse widths are within expected parameters. I’ve also verified all ground connections — including chassis-to-engine grounds — to ensure proper signal integrity. Thanks for the helpful input, everyone.

Anonymous 2010-08-11 16:18

Based on my experience, I'm facing a similar issue with my 2001 Tahoe. I’m not very experienced with car diagnostics and have a friend who is knowledgeable. Would you recommend visiting a dealership or having my friend handle the repair? Thanks in advance! — Larry Weddings Lake Tahoe

Anonymous 2010-08-11 17:35

Are you running the exact same truck with identical modifications? If so, check out a recent thread about a GM truck exhibiting P0306 and rich codes — it was ultimately traced to a failed fuel pressure regulator!