zachsdad1

Hi all. Looking for a little insight. I have a 02 C2 with 50k. Last night driving home, as I pulled in the driveway, my gas light went on. This morning I started it and a solid check engine light illuminated. I put fresh gas and went to a local auto parts store to read the codes with a generic reader. Three codes. P0300 P0304 P0306. Based on the previous threads in the forum, looks like there are multiple misfires on cylinders 4 and 6.

Could low/bad gas cause a misfire? Drove it to work after refueling and the car ran as smooth as ever.

I seem to recall on my boxster that the check engine light will reset itself after so many cycles. Is there any truth to that?

Thanks in advance for you help.

DBJoe996

Yes, the CEL will reset after a number of cycles and no more codes reported. Yes, bad gas will cause a misfire. Run some Techron in your fuel. Recommendation, buy a cheap OBDII reader, read the codes and erase them, then see if they come back.

zachsdad1

Thanks for the super quick advice. I appreciate it.

Macster

My info is that the DME will not register misfires if the fuel tank is low on fuel. I think this may be tied to the low fuel level warning light.

Bad gas could cause misfires. It would have to be pretty bad. (My only experience with "bad" gasoline came about when a family member's Infiniti sat one year while she was in the hospital. I drove the car once or twice (briefly) after she was admitted to the hospital and the engine started ok, idled ok, ran ok. But about 6 months after she first entered the hospital she gave me permission to use the car to drive our elderly parents around as I found them a place to live. The engine felt kind of sluggish, but being unfamiliar with the car and it being no Porsche I assumed this was the way it always felt. I drove the car enough though that the fuel tank level got low. I filled the tank with Shell V-Power (the engine required premium) and after the fill up the engine was transformed and remarkably too. It really impressed upon me how stale ("bad" I guess) gasoline could affect engine performance.)

Recently, a couple of times in the last month my 03 Turbo has misfired upon cold startup. I suspect it is a combination of old coils (they are original and have almost 125K miles on them) and the unusually humid air that has been around off and on for a while now.

What I do is check the error codes. (I have a device that connects to the OBD port and maintains a cell phone connection that sends this data to a web site that I can access from the comfort of my easy chair or desk chair so I do not have to go out and connect an OBD2 code reader (though I have one).)

I write them down and then erase the codes.

As long as the engine doesn't misfire after engine start say under hard acceleration or even just tootling around town, and the engine doesn't exhibit any other untoward behavior, I don't worry much.

'course, I have it on my list of things to do is to have the coils (and probably the plugs if they are due or near being due for replacement) changed probably next week some time.

Oh, and yes the CEL will be extinguished after so many warm up cycles provided the error condition does not reappear in that time.

zachsdad1

My thought was that perhaps some debris that may have been on the bottom of the tank was sucked in to the fuel system. Just a WAG since the tank was low. I'm going to erase the codes and monitor it.

Again, thanks for the input.

Jon Moeller

Like Macster, when my coils have been on their way out, higher humidity has exacerbated the problem. If it's raining, snowing, or humid, and you get the CEL's, you should start budgeting for replacements.

zachsdad1

what are we talking as far as replacement cost?

p.vanderlinden

Agree, I believe extra humid conditions here in SoCal kicked off similar codes to OP last month.

I cleared codes and similar ones popped up with next drive, though not exactly the same cylinders.

Replaced original 60k coils/plugs and all is well.

Cost was $350 for parts (Pelican). Not a fun job to do yourself (Pelican DIY). I would consider paying my trusted indy next time.

Took me about 5.5 hours (ex Indy, IMSA mech.!). If I were to do it again, it would take about 3 hours.

Best,
Paul

zachsdad1

good to know. Thank you.

zachsdad1

Was doing a little poking around and found this YouTube vi on replacing plugs and coils.

Imo000

Coils are ~$40 each if you shop around. If it was bad gas, all the cylinders would have been ranfomly misfiring. Could be also the spark plug gaps are getting big.

sjg1138

Coils and plugs solved the misfiring issues for me. It can definitely be intermittent. The job was a pain (maybe because I stubbornly would not take out the exhaust).

zachsdad1

Thanks. I was planning in doing the plugs with the 60k service. I picked up a code reader and cleared the codes. Been driving it all afternoon and no codes yet.

Thank you all for your input. I truly appreciate it.

Imo000

Don't worry, chances are it will come back. Cars rarely ever fix themselves.

Macster

There is probably some debris on the floor of the tank.

When my Boxster's fuel pump failed at around 200K miles (I think it was around then, I am forgetting and too lazy to dig out the repair invoice) at my request the tech checked the condition of the inside of the tank -- lucky for me the fuel level was quite low when the pump quit so the bottom of the tank was very visible once the pump was removed -- to determine if there was any need to completely drain (via a siphon) the tank to remove any water or debris and he reported no signs of water and very little debris. Not enough to worry about.

There was some debris stuck in the fuel filter, which in my 02 Boxster is the fine plastic mesh that is part of the pump housing. This housing attaches to the floor of the tank so the mesh portion is at the lowest point it can be.

The amount of debris was not scary and whatever finer debris made it past the mesh apparently hasn't affected the engine any, as the injectors are original and now with over 282K miles on them. The injectors have I believe their own filter consisting of a very fine metal mesh/screen that is designed to trap particles that would block one of the holes in the injector tip. Anything smaller would be injected into the chamber and eventually exit out the exhaust.

Bottom line is the misfires are from something else, most likely coils.

It is rare plugs cause misfires but you want to change these when due either from miles or time.