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1997 Chevy Tahoe P0303 Code: Cylinder 3 Misfire Diagnosis and Fixes

Model: 1997 Chevy Tahoe Fault Code: P0303 Posted: 2008-05-27 21:06

Hello! I'm new to this forum and seeking help with a persistent issue on my wife's 1997 Chevrolet Tahoe. The vehicle has 150,000 miles and is equipped with a 5.7L Vortec V8 engine. It passes the tailpipe sniffer test, but the Service Engine Soon light keeps coming back, preventing it from passing smog inspection. Before taking it to the smog shop, I replaced the spark plugs, plug wires, distributor cap, and rotor. After disconnecting the battery to reset the ECU, the check engine light appeared to go off. However, after driving about 15 miles, the light returned. The smog technician ran a dyno test and found emissions were elevated but still within passing limits. He then pulled diagnostic codes: a faulty second O2 sensor on Bank 2 (O2S2), and a P0303 code indicating a misfire in Cylinder 3. I replaced the O2 sensor and the #3 spark plug wire, again disconnected the battery to reset the system — the light went off. However, after returning to the shop, the check engine light came back on. The O2 sensor was cleared from the scan, but the P0303 code reappeared. A compression test showed Cylinder 3 at 125 PSI, which is within acceptable range (though not ideal). I replaced the #3 spark plug tonight and drove approximately 15 miles before the check engine light returned. I'm now wondering: what could be causing this persistent P0303 code? Any suggestions for next steps? Thanks, Ron

Related fault codes
P0303
Comments (7)
Anonymous 2008-05-27 21:17

Sorry for the double post — I also ran a can of Sea Foam injector cleaner through the last tank of gas, but it didn't resolve the issue. Ron

Anonymous 2008-05-28 07:30

The next step would be to perform a fuel injector leak-down test to verify that each injector is functioning properly and delivering the correct amount of fuel. However, this requires specialized equipment and access to the injectors, which are located beneath the intake plenum — making it challenging for DIYers without proper tools.

Anonymous 2008-06-03 21:06

I replaced both the #3 fuel injector and the upper intake plenum gaskets. After driving 30 miles overnight, I thought the issue was resolved. However, this morning when my wife took it to the smog shop, the check engine light came back on. I now need a fresh code read — if the P0303 code persists, what should I do next? This is becoming very frustrating. Ron

Anonymous 2008-06-11 17:10

If the spark plug and wire are new, it's possible that Cylinder #3 has a faulty fuel injector. I recommend checking the injector operation to confirm proper firing.

Anonymous 2008-06-11 19:03

I replaced Injector #3 with a new one — no improvement in symptoms or code resolution.

Anonymous 2008-06-11 23:54

Consider inspecting the MAP sensor. Remove the EGR valve and apply gentle pressure to its closed end (using your lips) — any noticeable leak indicates a problem. This is a basic mechanic trick, but can be useful. Also, some users have reported that replacing all O2 sensors helps in similar cases. I feel you — I’ve had the same issue with my 2003 Dodge Hemi and P0132 code. I used to live in a smog-heavy area and hated those emissions checks. Good luck — hopefully a dealership technician will chime in soon with a solution.

Anonymous 2008-06-13 05:17

For the Dodge, check your dealer for TSBs (Technical Service Bulletins). For the 1997 Chevrolet Tahoe, consult official GM forums or technical service documents to find known fixes related to P0303 and cylinder misfire issues.