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

 

My truck stalled at low speeds year back but it threw bad EGR code. I replaced it and it solved the problem.

 

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.

 

1- I put in Autolite Double Platinum plugs because Ive heard others tell me that the copper ones are garbage. Conflicting views.

2-All 16 were changed as well as the boots below the coil packs

3-Bosch O2 sensor

4-I did not check and wiring resistances and do not have an ohmeter as of now

 

1- Our Trucks do not do well with anything Except for Copper Core plugs... the coil pack systems are designed to see a certain resistance so when you go with Copper it has all kinds of misfire issues. There are million posts about it. So Get rid of the platinum plugs and go get some copper core plugs.

2 - Good

3 - Bosch sensors have been known to be crappy, same as Denso... if you can, get the OEM (from the stealership) or get an NGK O2 Sensor....

4 - Get one... or at least call a buddy and toss him a 6-pack to borrow it.

If he's a real buddy he'll even stick around to help.... lol

That's my recommendation make sure you check the wiring diagram in the service manual on Weedahoe's signature (he's a member on here) or on this link:

http://www.rambodybuilder.com/yearold.pdf

If it was my truck, I would change the plugs first, then I would change the O2 sensor to an NGK or OEM Sensor and see if it fixes the problem.

 

how do you check codes on a 2004 dodge ram 1500 5.7 hemi

 

Key dance trick..

Key "ON"/"OFF" (no engine start) 3 times, on the third time you leave it "ON".

In the odometer window, you'll see code popping up, if there are no codes or it's done, it will say "COMPLETE" or something like that.

 

I kind of doubt the platinum plugs are causing the multiple misfire but 16 copper plugs are cheap and probably worth the effort. Here is the number 2 step in the service manual to look at:
P0300-MULTIPLE CYLINDER MISFIRE (CONTINUED)
2. VISUAL INSPECTION
NOTE: Anything that affects the speed of the crankshaft can cause a misfire DTC.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinders Injector
Control circuit.
- Visually inspect the engine for any of the following conditions.
- Worn serpentine belt
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment of the Water pump, P/S Pump and A/C Compressor pulleys
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP, and TP Sensor mounting
- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector, Ign coil, etc.
- Vacuum leaks
- Restricted Air Induction system or Exhaust system.
- Internal engine component failures.
Were any of the above conditions present?
Yes >> Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 3

 

Do a search, there have been quite a few people that have had issues with misfires after installing Platinum Plugs.

The O2 sensor circuit is likely the issue, so the OP will likely have to trace out the heater circuit line to find the issue.

Misfires can be caused by a million and a half different things so it's a step by step process.

 

i have a 05 dodge ram with the 5.7 hemi in it, the truck has a rough idle but it smooths out after driving it amd its hot. i used sea foam to clean out the fuel system, ive done plugs to it (e3) and egr valve. im getting a p0300 misfire code and a high voltage 02 sensor. i check all the plugs oon it and they seem fine. also misted the coils to see if any of the coils where getting moisture in them but nothing. also checked the crankshaft sensors and both are reading dead on.