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1997 Chevrolet K1500 Vortec 5.7L P0302 Code: Diagnosis and Fixes - Vacuum Leak, Injector, or Engine Wear?

Model: 1997 Vortec 5.7 Fault Code: P0302 Posted: 2008-08-09 21:35

Hi everyone, I'm currently troubleshooting a persistent P0302 diagnostic code on my 1997 Chevrolet K1500 with the 5.7L Vortec engine. The issue is isolated to this one cylinder misfire, and no other codes are present. I've already performed several maintenance steps: replaced the fuel filter, fuel pump, A/C Delco cap and rotor, installed Delco Iridium plugs gapped at 60mm, checked all spark plug wires, replaced the EGR valve, and ran both Seafoam and Techron through the fuel system. The check engine light comes on solid (not blinking), typically after 3 to 5 days or as soon as 5 miles after clearing the code. The misfire is only noticeable at idle — there's a slight hesitation when lifting off the brake at idle, with minimal studdering during acceleration. However, while driving at higher speeds, the engine runs smoothly. This has become increasingly costly to fix. I'm now considering whether the issue stems from mechanical wear or a more subtle system fault like vacuum leaks or injector problems. I'm especially concerned about potential internal engine issues such as broken valve springs or wrist pins, given the intermittent nature of the misfire and the recent appearance of a rattle when blipping the throttle — which I now believe may be coming from the passenger-side valve cover. I plan to remove the valve cover tomorrow for inspection. Any insights into possible root causes would be greatly appreciated — especially in relation to the P0302 code on this specific engine model?

Related fault codes
P0302
Comments (5)
Anonymous 2008-08-10 08:00

Check for vacuum leaks at the intake manifold gaskets. The 1997 Vortec 5.7L uses a spider injection system, which is known to contribute to misfiring issues. A thorough inspection of this area may resolve the P0302 code.

Anonymous 2008-08-10 20:53

Update: This has become quite frustrating. Earlier today I suspected low oil pressure and ran Seafoam through the brake booster line, planning to switch from synthetic to conventional oil after an engine clean. After doing so, I noticed a new knock or rattle at startup. When blipping the throttle during deceleration, a distinct rattle is audible — it seems to originate from the passenger-side valve cover. This could indicate a broken valve spring or wrist pin. The P0302 code and low oil pressure may be linked. I plan to remove the valve cover tomorrow to inspect for internal damage. Could the Seafoam have cleared gunk that previously masked these sounds? Any thoughts on what this rattle might point to?

Anonymous 2008-08-10 22:22

Removing the valve cover and visually inspecting for broken components is a solid first step. Still, don't overlook vacuum leaks or faulty injectors — both are common causes of P0302 on older Vortec engines. A compression test or leak-down test could help identify internal engine wear. How many miles does your engine have? This information may influence the severity assessment.

Anonymous 2008-08-11 00:00

The engine has 126,000 miles on it — a significant number for a 1997 Vortec. Given the age and mileage, internal wear is a plausible concern. I'm not sure how to perform a leak-down test myself.

Anonymous 2008-08-11 08:00

Search online for 'cylinder leak-down test' — you can typically rent a leak-down tester at auto parts stores or mechanics shops. This test helps determine if there's internal cylinder sealing failure, which could explain the P0302 code and misfire symptoms.