OK fellas....here I come yet again scratching my head.I got a '05 Sporty 5.7 Hemi throwing a 0300 code.I switched out the plugs and wires.I don't think I have a burnt valve since I can feel no vaccum from either exhaust tip.Where to go/what to do now.I'm thinking it may be an O2 sensor but which one? I don't want to just guess and waste time and money.Any help or ideas as always are appreciated.

 

Are you using any excessive coolant?
O2 sensor could be it but that usually throws a specfic code for the O2.

 

No excessive coolant here.I just looked at the overflow tank yesterday and both the rad and the tank are where they should be.

 

My first thought was possibly a crank sensor, but it would throw a different code by itself.
Possible (?) water in the fuel???

When you did the plugs, did you get the plug wire overlay back in oem location----can cause problems like you're describing.

 

I'm assuming an overlay is where the wires run under the air intake on the top end of the engine.When I did the wires,I did them one at a time to make sure they all got the right routing and went exactly where they were suppose to.That way they wouldn't be sitting on top of something they weren't suppose to be and/or possibly arcing out either.My biggest problem with this whole thing is that the truck might not do this for another 2 months and then again it might happen tomorrow.Yesterday I took off the air intake and cleaned out my throttle body real good.It wasn't too awful.I've seen worse but I did it basically just to eliminate that as a possibility.I very well may have a bad computer too.I bought this truck from a dealership with 35K on it a few years ago so I don't know its history.I've also thought that maybe someone before me had the computer flashed and maybe the dealer reset it too OEM and that might be having an effect on it.I think if the 'puter was bad I would have a whole host of other problems too though.

 

Have you checked the connection condition for the computers, at least the ones under the hood?
If you go to Weedahoe's sig, you can download the FSM. This will give you the diagnostic procedures for testing the various components like the O2 sensors.

 

Thats a good idea.It never crossed my mind.The most irritating part outside of the fact that it's such a wide range of things that cause the random misfire is my truck might not misfire again for another couple months or more.It occurs very infrequently.When it does,I can stomp the gas and it just quits.(vaccum leak possibly?) Normally you can't even feel the thing runnin' while your in it though.

 

You might try putting some dry gas in the tank, (the red bottle only). If there is water laying in the bottom of the tank, you may be picking it up randomly.

Most vacuum leaks aren't random.

 

Agreed about the leak, and if you go through most of the Misfire threads you will see that 90% of people say when they stomp on it that you wouldnt even guess that it had a Misfire, i personally found out the same

 

So did you ever figure it out (what was giving you the misfire)?