P0304, then P0300??

[ChevLoRay]

My Service Soon light started flashing. Okay, that means there is a mis-fire. Then, it was steadily on. I get it. So, I hooked up my scan tool. Code P0304....number 4 misfire. Cleared the code. Drove to O'Reilly to get some plugs. While out and around town, there's an unevenness to the engine speed around 2K RPM's.


Got back home, changed out the 3 plugs on the right bank and fired it up. I had cleared the codes before starting it back up. This time, I get a P0300...which is a random misfire.

Didn't change the cap/rotor, but maybe this random misfire is a clue. Trying to be logical, it's the only thing that I can think of that is common to the ignition system and has the job of getting the spark to the plugs.

Anybody ever try to get logical with an HEI? Yeah, I'm going to change the other plugs and get a cap/rotor. Just wondering how other folks do with their analyzing.

[scotts62]

I would just change the cap and rotor and see what happens, worst case it could be the distributor like on mine but it steadily came one and not just a "bam" it was there like in your case.

[ChevLoRay]

Thanks, Scott. Yeah, that is the plan. I was just looking for someone who may have seen something like this. Since I changed plugs, I haven't had a Service Engine light, but I'm not convinced that it is all plugs. It had a set of Bosch plugs with twin tips on them, but I went back with RapidFire AC's, which are platinum. I always had good luck with them in my '69.

[danomano]

Worn distributor gear? Maybe?

[ChevLoRay]

Thought about the distributor. It was replaced in CA in '05. Right now, it's working just fine. I'm thinking that a consistently-worn item like a distributor would throw some codes relative to the distributor. This issue is too random.

[scotts62]

Yeah if it was the dizzy it would be a constant problem. I think its just the typical parts that wear.

[ChevyTech]

I would guess this is the 1996 you have listed at the bottom of your posts being it has OBD2 codes.

Definitely consider the distributor cap and distributor gear wear and others have suggested

Try turning the distributor rotor back and forth while you have the cap off to see if the gear is sloppy.

You may want to try spraying a water mist on it with a spray bottle at night and watch for sparks. You will see little sparks, but look for big sparks that cause a cylinder to drop.

Another thing to consider is a fuel nozzle that is dirty or leaking. It could have a poppet valve leaking at times. I am not a fan of the central port fuel injection systems. Has your system been upgraded to the system with 8 injector and no poppet valves?

[Old Money]

my sons 97 4.3 was hard on cap and rotor. the cap was wearing uneven after 6000 miles, came time to inspect distributor gear. it was showing severe wear on one half and normal on the other. 180,000 miles any many start ups. a computer engine only starts on no. 1 cyl. replace gear on dist. or by a reman- dist. it always coded PO300 random missfire until it got so bad it would not fire. it would almost sound like timing chain wear. old money.

[ChevLoRay]

All my moderating and I didn't even list my vehicle.....ChevyTech...thanks for reminding me.

It is the truck in the signature, but it is equipped with a 4.3 and 4L60E. My bad for not putting that in the original post.

I'll be sticking a new cap and rotor on it, this weekend.

As for the injection system, nothing has been changed that I am aware of unless my son had something done in California. I'll ask him. I vaguely recall something about the CPFI while he was out west, but I don't know anything specific.

Thanks for all the feedback.