P0301 Misfire Diagnosis on 2002 Chevrolet Tahoe 5.3L Vortec: Fuel System or Injector Issues?
Hi everyone, I'm new to this forum and usually work with diesel engines, but I'm now troubleshooting a persistent P0301 cylinder 1 misfire on my wife's 2002 Chevrolet Tahoe with the 5.3L Vortec engine. The vehicle has around 99,000 miles and is running smoothly under normal conditions—good power, smooth idle, no roughness at low RPMs. I replaced both spark plugs and ignition wires as a first step, which didn't resolve the issue. I then swapped cylinder 1 and cylinder 3 coil packs, but the P0301 code remained unchanged, indicating the misfire isn't being triggered by a faulty coil. The engine only shows a solid check engine light below approximately 1500 RPM, and it flashes above that speed—this is concerning because flashing codes typically indicate severe misfiring. Despite the smooth operation at idle, I suspect an underlying fuel system issue. I'm considering using carb cleaner to test for carbon buildup in the intake or injectors, as some users have noted increasing issues with modern gasoline quality affecting injector performance. My questions are: 1. Is a fuel filter replacement warranted at 99K miles? If it's clogged, could that cause a P0301 misfire? 2. How difficult is it to replace the injectors on this model? Can a professional shop perform an injector flush or replacement? I've heard that Vortec engines—especially older models with CSFI (Cylinder-Specific Fuel Injection) systems—are prone to issues with injector lines and nozzle clogging due to fuel contamination. I also recall some reports of misfires linked to plugged catalytic converters, so I'm considering checking that as well. I've confirmed the engine is a Vortec 5.3L, though I need to verify if it's an older CSFI or newer SFI design (which may have different injector inlet issues). Any advice on diagnostics—such as fuel pressure testing, O2 sensor monitoring with a scan tool, or checking for vacuum leaks—would be greatly appreciated. Thanks in advance! Digger T.
Before diving deep into injectors or fuel system components, confirm whether your Tahoe has a Vortec engine. If so, it's known to have issues with CSFI (Cylinder-Specific Fuel Injection) systems—especially the injector lines and nozzle-style injectors that are prone to clogging over time. If compression tests show good results and there are no vacuum leaks from intake gaskets, consider swapping cylinder 3’s injector with a known-good one. If the P0301 code moves to cylinder 3, it strongly suggests a faulty injector. I’ve also heard reports of misfire codes appearing in Tahoes and Trailblazers when catalytic converters are plugged—worth checking as a potential cause. The flashing P0301 light typically means significant misfiring, not just minor issues. Ensure fuel pressure is within specifications; if it drops quickly when the key is off, there may be a leak in the injector line or at the injector itself. Also, some mechanics have mistakenly crossed fuel lines during intake gasket repairs—be cautious of that. Lastly, use only OEM distributor caps for this engine model. Aftermarket parts can sometimes cause electrical issues. Make sure you used quality spark plugs and wires during your tune-up as well. A fuel filter replacement is definitely recommended at 99K miles—it's overdue—but if fuel pressure is low, it won’t solve the problem. Bad fuel pumps are also common in these trucks. I’m not an expert on GM systems, but this seems like a classic case of injector or fuel delivery issues. Good luck—please update us on your progress!