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1998 Chevrolet Venture P0304 Code: Miss Fire, Diagnosis & Repair Steps

Model: 98 Venture Fault Code: P0304 Posted: 2011-02-27 08:40

Hello everyone, I'm working on my 1998 Chevrolet Venture with a 3.4L engine (159,000 miles). About eight months ago, the engine started misfiring, and the check engine light came on. A scan tool revealed multiple misfires. The next day, I took it to a shop—they flushed the fuel system, replaced the fuel filter, cleaned the TBI and MAF sensors. It ran well for about two months before the check engine light returned. A few days later, during acceleration, the light began flashing, and the OBD2 code P0304 appeared. I took it back to the shop, who diagnosed a vacuum leak and a faulty injector, recommending a complete top-end rebuild with new intake gaskets—costing $1,400. After researching, I decided to do the work myself. I disassembled the engine, replaced both lower and upper intake gaskets, cleaned all lifters and pushrods, swapped out cylinder #4 injector, and cleaned the other injectors (at the time, I didn’t realize I needed to replace all of them). I also replaced all oxygen sensors and all O-rings during reassembly. After reinstalling with new seals, gaskets, plugs, wires, air filter, and cleaning TBI and MAF, everything seemed fine. It ran smoothly for about two weeks—then the check engine light returned, flashing during acceleration. I scanned again: P0304 persisted. I then disassembled the engine again to inspect the fuel rail, swapped injectors #2 and #4 (original positions), replaced the fuel pressure regulator, checked harness resistance, and reassembled. After clearing codes, the engine started well but immediately showed a return of the P0304 code—misfire still present, especially under load. I then swapped back to original injectors (#2 and #4) in their original positions, flushed the fuel rail, replaced O-rings, and let it sit for several days. Now I’m planning to check ignition coils and cylinder compression before considering another shop visit. Any insights or suggestions would be greatly appreciated—especially on diagnosing P0304 specifically on a 1998 Venture with a 3.4L engine.

Related fault codes
P0304
Comments (4)
Anonymous 2011-03-02 17:54

I performed a compression test on cylinders 2, 4, and 6. Cylinders 2 and 6 showed approximately 110 psi each, while cylinder #4 read about 95 psi. After injecting a small amount of oil into the cylinders, readings increased by roughly 5 psi—indicating potential valve sealing issues. I then tested spark with plugs removed and then with new plugs installed. The spark color was consistently yellow for all cylinders (1, 2, 3, 4, 5), which suggests normal ignition but not strong combustion. Given that all plugs and wires are new, I’m considering replacing all ignition coils next. If that doesn’t resolve the issue, I may need to inspect the ignition base. Any advice or suggestions would be helpful—thank you in advance.

Anonymous 2011-03-03 06:20

Before investing in a new coil pack or module, try testing with a used one from a salvage yard first. If the problem persists after that, it may point to a faulty valve or spring in cylinder #4—especially since P0304 is linked to that cylinder.

Anonymous 2011-03-03 18:51

Thanks for the input—I’ll check this out over the weekend and update with results.

Anonymous 2011-03-04 14:14

Be aware that the 1998 Venture’s engine has two different lengths of pushrods. If during reassembly you installed the intake or exhaust incorrectly, it could cause a misfire. Also, there's a known TSB regarding torque specifications: after tightening to 14 ft-lbs, the rockers should be torqued an additional 30 degrees. Failure to follow this can result in valve float or back pressure issues—leading to misfires like P0304. I recommend reassembling carefully and verifying component alignment before continuing.