jkelley

Good morning again all,

I have been trying to get my 05 to tip-top shape but I've been running into a few issues.
Last night the check engine light came on. Check it with scanner and got a P0303 and P0303 P code. Looked it up: Misfire on cylinder #3.

Now I had the same CEL code P0303 about 3 weeks ago (about ~2 weeks after buying the car ), but just reset it to see if it would come back. I figured it was due to some bad gas (I went to a different, more sketch station to fill up... where probably not a lot of people even use the 93 octane they have, so figured it was partially spoiled or something) or a spark plug issue. So I changed all 4 spark plugs because I wanted to anyways. All was good for 2,500 miles, which was last night when the CEL came back, same code.

Series of events:
- Due to some "rough" idling in neutral (really not that rough, but I want the car running at 100%) I added one of those Valvoline intake and fuel injector cleaner bottles to my tank with ~5 gallons of fuel already in the tank and then immediately filled the tank with fresh gas to get it good and mixed (As the bottle recommends).
- I drove ~1 mile home and then reset the ECU (which in hindsight I rpoabbly shouldn't have done with "altered" gas in the tank, but it shouldn't be too big of a deal) by pulling the fuse for ~5 minutes. I whacked the MAP sensor too, while the ECU was out). Then plugged the fuse back in.
- I then drove to the gym ~3 miles away with no issues, it actually felt like the car was running noticably better!
- When I left the gym and started the car, that's when I noticed the check engine light P0303 code - misfire on cylinder 3.

So now what I'll be doing is resetting the CEL, and swapping coil pack #3 with another cylinder to see if it's a coil pack.

My questions are:

1. When I reset the CEL and swap a coil pack, is there a preferred cylinder to go to?
2. Is there a quicker way to test a coil pack, some other method?
3. If it IS a coil pack, should I not be driving the car? I drove it to work this morning and it feels like it's running great I'm not going to order another coil pack until I know that's what it is, so can I drive the car for ~1 week while I find out and order the part?

Thanks in advance! and sorry for the long post! I just like to give all the information I have

MM3Kwolik

You'd know if the cylinder was completely dead in which I wouldn't be driving it. Chances are you have a part that is just beginning to fail (most likely a coil pack) and is intermittently not giving you spark. Just swap it with any of the other 3 and see if it migrates, if it does, you know that's your issue. I wouldn't worry about it TOO much if the car seems to be running and driving fine.

jkelley

Ok cool. Yea that's what I'm going to do tonight as soon as the block cools off after driving home (another late night in the garage it seems )

I forgot that one of my quesitons was also if the additive would cause a misfire?
The bottle says it's distillates from gasoline basically (which I'm assuming is just methanol, ethanol, maybe some propanol and/or decane/hexanes?) but I would think that stuff would spark relatively easily compared to a long hydrocarbon molecule like gasoline?

Do you think that had anything to do with it?

MM3Kwolik

Injector/Fuel System Cleaners will not/should not cause any sort of misfire. Would kinda be the opposite result of what they're designed to do.

jkelley

That's what I figured, the stuff in that are super "light" volatiles so it should ignite with minimal ignition energy.


So my current status is:
- I walked out to my car after work yesterday and started the car. Let it warm up then turned the car off.
- Popped out the backup fuse for 5 minutes to reset the check engine light and clear the ECU I guess.
- Popped the fuse back in and started the car. The check engine light was there right on startup...
- I dropped back down into the footwell and pulled the fuse again (with the car off).... the dang fuse was blown??? When I pulled it a couple times in the past few days I never really checked it because I assumed it was fine. In hindsight, that was incredibly dumb of me, I know.
- Anyways I grabbed a spare 7.5A and popped it in. I decided to reset the check engine light from my ODBII scanner instead.
- Started the car and let it idle for about 5 more minutes before taking off. I drove home ~15 miles away.
- When I got home I still had no CEL (from the earlier reset). So I turned the car off for a minute or so, then started it back up. No CEL. I did this only because each time I got a CEL it was from startup rather than mid-driving.
- I let the car cool down for a few hours in the garage and then went back to swap the coil pack, so I swapped cyl 3 with cyl 1. Started the car again, no CEL.
- This morning I went to the garage to get ready to go to work, thinking that maybe the CEL is being thrown on cold starts versus warm? Nope, no CEL. Drove to work and still no CEL. Car drove fine and everything too. Idle was fine as well.

So I guess at this point I really still don't have a clue what it could be Both times that I had the "initial" CEL for the misfire it was on the second start after a fill-up (on cold start).
Also, I'm thinking that the stupid backup fuse was blown all along, since I've had the car... I think the prev. owner may have thought back-up meant spare, and threw some other blown fuse in that slot versus throwing it away.

Has my car been running without the ECU doing any learning?

MR.T

Did you check the code after you found the blown fuse? You could of blown it while pulling and installing it and maybe that's why your cel popped back on.

Very interesting though. Love to hear some guru's interpretation.

jkelley

Yea I still checked it (my scanner you have to before you can erase it), it was still the P0303.