Getting an MIL Error Code P0300

[wayoflife]

I got a MIL the other day and according to my OBDII reader, it's a P0300 or multiple cylinder misfire code. Now, I should point out that I have been having some engine issues or maybe more specifically fuel system issues recently. For one, my engine tends to idle roughly at start-up. Also, I've been getting some pretty bad MPG lately and it seems a bit sluggish when climbing long hills and I typically smell rotten eggs during these climbs.

So, here's what I've done so far. I have run fuel injector cleaner, Sea Foam, changed out the spark plugs (old ones looked good), cleaned out the throttle body, had my cat compression checked (good), replaced the O2 sensors, CPS and most recently, the TPS. I'm starting to wonder if maybe I need to replace the spark rail (coil pack) but don't for sure. Anybody else ever experience a problem like this or have any suggestions?

TIA :cool:

[CHOPPER]

Hey there Eddie,I see that you have had this line in the water for a while but you haven't had any bites:D Did you get it taken care of yet? What did you find?? If not, it sounds to me like you may have a couple of different problems going on. My knowledge of the jeeps is pretty limited, but I'll do my best to throw some ideas at you that might help you to figure it out. That is if you haven't all ready.

You say that you get a rotten egg smell climbing hills and it runs sluggish.
Most of the time a catalitic converter will create a rotten egg smell when it's bad. Check this out...I knew a guy that had a inner piece of his catalitic converter come loose, and from it bounceing around in there, the loose piece eventually became a ball that would intermittently block his exhaust which would make the vehicle run like crap at times, especially if he was really putting his foot into the gas. The flow of the exhaust would pull that loose chunk right twords the open hole like water going down a shower drain, and the chunk would just plug it up. We had a hell of a time figurimg that one out.

I know that this is gonna sound like a dumb question, but it's the first thing I would have checked, and you didn't mention it in the stuff you replaced so far.... When was the last time you changed your fuel filters and also your air filter. Injector cleaner won't clean a dirty fuel filter, and your OBD2 wont tell you their dirty either.
Also have you checked for any vaccuum leaks?

Oh yeah, I was also wondering...The code that you pulled out...Was that the only one in the system? If there were more please list them all no matter how irrelevant they may seem.

Also what's the vehicle year...model....and type of engine, and how many miles on it?

I hope this stuff helps you ,
Good luck for now,

CHOPPER

[wayoflife]

Thanks for getting back to me CHOPPER. I have a 2000 TJ with 4.0L and the code I got was the only one.

To date, I've had the O2 sensors replaced, TSP replaced, CPS replaced, Throttle Body cleaned out, spark plugs replaced, compression test done on the cat (it's good), replaced air filter, have run FI cleaners a couple of times and most recently, replaced the coil pack (spark rail). This last replacement seems to have helped out big time with power and the smell but I still do get a rough idle from time to time.

Next on my list is to start replacing fuel injectors but considering how much they are a piece, I was kind of hoping I would just get a code to tell me which one needs to go. Oh well, I guess I'll just have to be patient. :sad:

[CHOPPER]

Thanks for getting back to me CHOPPER. I have a 2000 TJ with 4.0L and the code I got was the only one.

To date, I've had the O2 sensors replaced, TSP replaced, CPS replaced, Throttle Body cleaned out, spark plugs replaced, compression test done on the cat (it's good), replaced air filter, have run FI cleaners a couple of times and most recently, replaced the coil pack (spark rail). This last replacement seems to have helped out big time with power and the smell but I still do get a rough idle from time to time.

Next on my list is to start replacing fuel injectors but considering how much they are a piece, I was kind of hoping I would just get a code to tell me which one needs to go. Oh well, I guess I'll just have to be patient. :sad:

I'm glad to hear that replacing the coil pack helped. Although when you said in your first post that you got you cat compression checked, I must admit that I thought that it was possably a spelling error or something, because I have never heard of getting the cat compression tested. The cylinders of the engine...yes. But the cat...no. I'm guessing that that test is just to make sure that the exhaust gasses can flow freely through the cat to make sure that there's not too much back pressure in the system.

Since you think that you may have one or more bad injectors, if you can somehow indivdually dissable one injector at a time when the engine is ideling roughly, that is one way to find a bad injector. Because if you dissable a injector thats good the engine will start running worse. If you dissable an injector that's bad, there will be no change in how the engine is running.

[CHOPPER]

I just thought of another thing...Make sure all of your battery connections are clean and tight. And when I say battery connections I'm also talking about the connections at the starter and all frame and engine ground connections as well. So many electrical problems arise from dirty and or loose positive and negative cable connections and they tend to get overlooked.

[offroadaz]

Thanks for getting back to me CHOPPER. I have a 2000 TJ with 4.0L and the code I got was the only one.

To date, I've had the O2 sensors replaced, TSP replaced, CPS replaced, Throttle Body cleaned out, spark plugs replaced, compression test done on the cat (it's good), replaced air filter, have run FI cleaners a couple of times and most recently, replaced the coil pack (spark rail). This last replacement seems to have helped out big time with power and the smell but I still do get a rough idle from time to time.

Next on my list is to start replacing fuel injectors but considering how much they are a piece, I was kind of hoping I would just get a code to tell me which one needs to go. Oh well, I guess I'll just have to be patient. :sad:

Hey Eddie, sorry for bringing back such an old post but Im facing the exact same problem on my 01 TJ. Did you ever get yours fixed?