Originally Posted by ricksss96

But follow magnethead’s tip and fix the O2 sensor problem first, then tackle the Evap problem. Check your harness to the O2 sensors. Since two different sensors are throwing codes it seems unlikely they both went bad at the same time. Look for broken/melted harness wires, bad or loose connector. Know how to use a VOM? Unplug the connector at the O2 sensor and look back into the harness and you will likely see the problem as an open or a short circuit. After you have verified the harness is OK, then spend money on new O2 sensors if needed.

BTW, the reason it runs when you mash the pedal to the floor is that the PCM switches to open loop control and ignores the the O2 sensor output.

Originally Posted by Robertwav1

The 3.9L magnum. Gotta love this engine. I had similiar codes, did a tune up and changed O2 sensors. Still had the problem so I took off the intake....waste of time as it was tight but redid it anyway with new gaskets. Easy engine to see if it's a vacuum leak or not. You can more or less seal the intake holes and ignore all the vac lines just to see if it solves your problem. I've been through this.....no vac leaks causing the problem for me. Sensors for this engine are really inexpensive and there are not that many. The hardest to change is the crank position sensor. It takes allens by the way should you decide to change it but you can't see them. The bolt is a hex head but again if I would have known the allens were there it would of made it a lot easier. Anyway.....I had a bad crank sensor and to make things worse I had to do it twice before I got a good one from advance I believe it was. Misfires and codes were all over the place but never an indication of a bad crank sensor. The only thing that led me to this was the timing jump looking at live data on an actron scanner. It went fron like 14% and then jumped to 23%.....something in that order. It sort of led me to a timing problem and on this engine the cam sensor and crank sensor are responsible for this. Hope this helps.

Originally Posted by Skreelink

If it's been awhile, I'd start with a full tuneup, plugs, wires, cap, button, air filter, and O2s (especially since you have a code). This could rid of basically all your codes minus the P0455. The O2 sensors being clogged could indeed lead to a rich system, or at the same time, be fouled by a rich running system. Worn plugs/wires/cap/button would cause a weak spark and not burning all the fuel, leading to the O2 reading a rich system. Similar if your air filter is clogged, it's not getting enough air so too much fuel. You'll want to get it done before too long as a rich system and unburnt fuel could lead to a damaged catalytic converter, and that can be an expensive fix.

For the EVAP code, P0455, double check or simply replace the gas cap. The rubber seal could be cracking or simply not holding tight enough to seal the system. Most common evap codes are from a bad fuel cap. Otherwise, vacuum lines between the tank, charcoal canister, and purge valve on the firewall. I was getting P0300, P0301, 303, and 305 (all bank 1 cylinders) if I ran over 70mph, turned out the purge valve was upside down, hasn't returned since flipping it (still testing, been a week, here's hoping). I would assume it being bad/leak could cause it as well.

Best of luck, at least all these repairs are fairly cheap and decently easy.

Originally Posted by aaron7

Was worried about doing the cap as someone told me if one of the screws snaps you have to pull the motor to get the dist out?? Doesn't look to be much room if I had to drill, kinda believe it.