Originally Posted by Amerce
Hello, I'm new to the forum. Just picked up my first dodge yesterday. It came with a check engine light that I thought would have been easier to fix.
I scanned it and got P0300- Multiple misfire P0155- I believe oxygen senser.
I have replaced all spark plugs, coil boots and wires, as well as the upstream o2 sensor on the passenger side. I reset the light and both came back on just driving down the block.
Since I've already replaced the o2 sensor, I believe the misfire has to be throwing that code as well but I have no idea how to get rid of it.
Some background on the truck-- K&N air intake, flowmaster exhaust, 3.5" Fabtech lift, 35" Nitto Mud Grapplers. The truck has stalled when turning at very low speeds a few times and I cannot actually feel/hear a misfire although I do not have a very trained ear for it. I read on the other post about P0300 to put in high octane gas, I put in 87 but do not think that would throw these codes.
Any help would be much appreciated
Okay well First off Welcome to Dodge Forum!
Now then, a few questions to help us out here.
1) What type of plugs have you put in? (if they are anything but COPPER CORE plugs, change them for Copper Core plugs ASAP!)
2) Did you change all 16 of the plugs or just 8? (The Hemi Engine has 16 Plugs, 2 for each cylinder)
3) What brand O2 sensor did you replace the OEM one with?
4) Did you check the resistance over the O2 wiring on the truck side?
Most common wires that are the heating circuit are black or blue... I've seen a few that are wire or purple, but those are usually for imports. Those are usually on the O2 sensor side so just match up the connectors and test the heating circuit to ground. If you get a really high resistance then there is likely a short downstream on either the heater wire or the ground. Most common "short" is a chaffed or melted wire.
Also, use 89 Octane... The owners manual suggests that you use 89 Octane for the 5.7L Hemi.
If the previous owner had put an aftermarket performance tune on the truck it will require 91 or 93 octane which can definitely cause you to misfire (knock) with lower octane fuel.
Answer those questions if you can and we'll see where we can go from there.