So I have been having issues with P0304 coming on. Guys doing work on my car said there was a loose pin when they were connecting fuel injector 4 back and that it might be loose or need replacing. I put in both a new fuel injector and spliced in a new connector and the check engine light went away... for about 50 miles. Then it came back on. I tried new spark plugs, swapping the plug wires but the code remained on cyl 4. I tried putting in a new coil pack and still no change:

When running, check engine light is simply on, giving me P0304. When I start to idle for a little bit, it begins blinking and issuing the P2097

I know that the O2 sensor on my car has given me trouble and am looking at that next, but if it's not that I'm not really sure what to do next??

 

Welcome to the 2nd Gen Neon forum

You've been busy on this puppy. 154 reads but no replies, so I'll see if I can get things started. Good idea to have scanned for & posted the code Numbers & detail about when the P2097 shows up & the flashing P0304. SO with those clues & the definition of what those codes suggest, lets see if we can discern something meaningful to put high up on the suspect list.

P0304 is for cylinder #4 & it flashing indicates the ECM has detected a misfire & thats not good for the cat converter, as its having to process unburned fuel & that can cause the converter to overheat & melt down inside & that can cause excessive exhaust back pressure & the engine to loose power, run hotter than designed for & cook the oil, mess with the exhaust valves & head &....well you get the idea, you know its something that needs to be put right without delay!!!!

The P2097 code says the O2 sensor is reading an overly Rich condition in the exhaust stream, so is confirming the P0304 flashing CEL / misfire condition. Question is, what's causing the cyl 4 misfire????

Did the problem come about suddenly after some event. When its misfiring can you hear any mechanical noise thats not there when its not misfiring???

 

Thinking about this some more, it seems to me the P2097 code for the O2 sensor detecting a Rich condition in the exhaust gas flow, is suggesting the #4 fuel injector IS squirting but you have spark going missing. SO, to confirm, use your inductive timing light on the #4 spark plug wire to safely let the timing light indicate the misfire. If it does indicate its spark going missing, we next need to think what to move higher up on the suspect list. Seeing as how you've replaced the plugs & coil pack but I see you said you just swapped the plug wires around, not yet replaced them, so I suppose we have to include them as suspects & then I suppose that lastly leaves us looking at the #4 coil pack ground switching driver in the ECM, as going intermittent, so it goes on the suspect list too.

I suppose you could try back probing the #4 coil pack ground lead using a test light to see if it misses a blink when the driver misses a beat thats in time when the miss occurs.

More thoughts for consideration, let us know what you find.

 

Thinking about this some more, it occurred to me that the coil pack ground lead to the ground switching driver electrical connector at the ecm could be open & if so, the #4 primary winding isn't going to be ground switched, thus it won't make any spark. SO, you could use your multimeter to check that lead end to end for continuity.
If continuity checks out ok, then put your multimeter on the 20 volt DC setting, connect the leads in series with the #4 primary ground lead, crank the engine & see if you read voltage as the driver ground switches that coil to make spark. If you can't get a reading, then it suggests the ground switching driver isn't working.

So, if you know someone with a like equipped Neon, you could try swapping in their ECM & see if #4 coil will make spark.

Or you could have a electronic tech swap out the suspect driver in the ecm for a known good one & see if #4 will wake up & make spark.
Or opt for a salvage yard ecm, as you could try it at the yard.
Or opt for a reman ECM with a warranty. More rambling thoughts for consideration, let us know what you find.