Hello all I am new here to the forums. I have a 2004 Dodge Ram 1500 with the 3.7l 5 speed transmission. I picked up this truck back in Sept of 2023 with 216000 on the miles. Current mileage is 227736.When I got it it had codes for a random misfire(P0300) and P0305. I’m thinking no problem it just needs new plugs and coils. I have changed all the plugs and coils yet this truck still gives me a random multiple cylinder misfire. When I start it up it starts to hi idle a bit then the motor starts shaking as the check engine light flashes. Also I can hear it spitting out the tail pipe. I also have two other codes not related to the misfire. P0138 and p0132. I know those are for the o2 sensors. I had it hooked up to a professional scanner and the o2 sensors are reading just fine. After the truck is done with the motor shaking it runs fine on the freeway and the road. I can’t thank of anything else that would make this truck act like this. Unfortunately this is my daily so I do not have other vehicle to get me around to work etc. Also since this truck has a lot of miles on the motor I am considering pulling this 3.7 out and swap it for a 4.7 or 5.7 hemi. If I were to take that route, what would be the best option? What am I looking at getting to complete the swap? What cost am I looking at to get everything done? Thanks in advance.

 

The flashing CEL is telling you the engine is misfiring. If it starts doing so immediately at startup.... it should be easy to find. If it NEVER runs smooth, I would be real tempted to recheck wiring to the coils, make sure they are plugged into the CORRECT coils. What plugs did you install? These engines are notorious for not getting along with the Rare Earth spark plugs.... If all that checks out, do a compression test in number 5. See what ya get.

 

So it starts the shaking upon start up but then after it’s been running and warmed up it doesn’t do it anymore. It runs smooth once I get going down the road. I installed E3.56 diamond fire spark plugs. Before I installed these I found a mixture of champion Ngk and auto lite spark plugs I’m guessing from the previous owner. As far as compression test on cylinder #5 I will see where I can have this done as I’ve never done a compression test on a engine.

 

Ok, theoretically those are copper core plugs.....

Wonder if you have a sensor that is misreading when the engine is cold???

 

The only sensor I can think of misreading are the o2 sensors. I do have 2 codes for those but as I mentioned earlier I had the truck hooked up to a professional scan tool and the o2 sensors were reading fine also it couldn’t find which cylinder was misfiring. This is what confuses me about this engine. I’ve never had one act like this.

 

PCM ignores the O2 sensors at startup, usually, its a couple minutes before the heaters in the sensor get them working properly. A fair few sensors have failure modes that the PCM won't detect. It really has nothing to compare them to.... so, if the reading is wrong, but, reacts the way the PCM expects when you step on the gas, or whatever.... it just 'assumes' that reading is viable. Which makes troubleshooting just so much fun....

The P0305 code is misfire on number 5. Think I would start looking there.

How long after startup before idle smooths out?

 

Hey sorry for the delayed response. So today after startup it actually started to misfire 30 seconds after the engine has been started. It goes on for about 2 minutes before the idle smooths out a bit. Now lately it seems to idle at a higher rpm than before. Normally it idles around 799-750 rpm. Now it wants to idle close to 1k and sometimes higher. I have to turn the truck off then back on for the idle to go back down. As of now it doesn’t have P0305 it only had it when I first bought the truck. After I changed all the coils and plugs that specific code went away and I’m still with P0300, P0138 and P0132. Those are my only codes showing up on my scan tool. As far as the high idling I can’t get a code for the IACV so I don’t know what is causing that issue. I have a video I took of the truck misfiring I tried to upload but I can’t because it’s not a supported file type. If you have a way to send you this video maybe it could be of help to better troubleshoot.

 

Is yours electronic throttle? Or is there actually a cable to the throttle body?

 

There is a cable to the throttle body. I don’t believe it’s electronic.

 

So much for that thought.

Might do a thorough cleaning on the throttle body to start....