Check engine light on

Good evening,

The 304 code is for a cylinder misfire for cylinder four.

Below are possible reasons for the code.

How old are the tune up parts?

Could be as simple as a spark plug but needs to be checked.

I would also have the compression tested, injector tested and a good look for any vacuum leaks.

Roy

A misfire is caused by a failure of combustion. When this occurs, unburned HC and excess oxygen are exhausted from the cylinder. Consequently, the catalytic converter may suffer damage through overheating as it tries to convert the excessive HC. Secondly, the O2S will report a lean condition to the ECM, which in turn will increase the injector pulse width and add more raw fuel to the exhaust stream.

The misfire detection monitor is continuous and is designed to detect levels of misfire that can cause thermal damage to the catalyst and/or result in excessive tailpipe emissions. Determination of a misfire is made by analysis of changes in crankshaft speed, a misfire causing a drop in acceleration after an anticipated firing event. This data is analyzed in four ways to ensure all possible combinations of misfire can be detected.

The results of the misfire judgment process on each firing event are used to determine whether two failure levels have been met, 'catalyst damage' misfire and 'excess emissions' misfire. Each fault judgment process has its own failure threshold and calculation period.

Monitor DTCs
P0300 Random/multiple cylinder misfire
P0301 Cylinder 1 (1 bank 1) misfire
P0302 Cylinder 2 (1 bank 2) misfire
P0303 Cylinder 3 (2 bank 1) misfire
P0304 Cylinder 4 (2 bank 2) misfire
P0305 Cylinder 5 (3 bank 1) misfire
P0306 Cylinder 6 (3 bank 2) misfire
P0307 Cylinder 7 (4 bank 1) misfire (V8 engines only)
P0308 Cylinder 8 (4 bank 2) misfire (V8 engines only)
P1313 Catalyst damage misfire, bank 1
P1314 Catalyst damage misfire, bank 2
P1316 Excess emissions misfire

That is possible but it will not cause the code.

The way to check them is to have a back pressure test done.

You or a shop would remove an O2 sensor and put a gauge in the place and run the engine. If the pressure is any more than 1.5 lbs, the catalytic converter is clogged and needs to be replaced.

Roy