I have been having some issues with my 07 3.7 Dakota. It has 133,000 miles. Initially I had a cyl 4 misfire caused by a supposed bad fuel injector. So I changed the fuel injector and put it back together and started it up. Now I have a P300 code. Checked it with the OBD2 and now there's a cyl 4 and cyl 5 misfire. I got frustrated so I took it to the Dodge shop right next to my house and had them look at it. They checked compression and threw a noid light on it and decided to move injector 5 to injector 1 which cleared up the misfire on cyl 5 and moved it to cyl 1. I was told to change the injectors on 4 and 1 and if I wanted them to do it, it would be a cool $1000. So I changed out injector 4 with the one that was in cyl 2 and put brand new injectors in cyl 2 and cyl 1. Now I have a misfire in cyl 1 and cyl 2, where the brand new injectors are. It mostly only misfires at idle and it does sound a bit like a diesel engine for some reason.

TL: DR Misfires on 1 and 2 at idle even with brand new injectors.

 

did you replace the fuel injectors with OEM? or with a different make/model injector? if the flow rate is different then the OEM injectors, it might be putting too much or to little fuel causing your misfire. I would think too much based on how it's only at idle.

 

I tried both Bosch and Standard Ignition as new replacements. Swapping the known good ones has produced the same positive effect every time and putting in the new after market ones (Bosch and Standard Ignition) have both given me misfire at idle issues. So I agree that it might be the non OEM injectors are not up to spec. Would the misfiring affect the engine to make it sound sort of like a diesel?

 

This is my line of thought also. Possible cylinder fuel flow imbalance. Even old vs new may have different spray pattern just from age. Replace them all with matching set.

 

This was where I was going to, the computer might not be able to figure it out when it's just a few cylinders getting the excess fuel.

 

I had realized that at some point, presumably over a decade ago, a P/O had installed Mopar fuel injectors from a 3.3 / 3.8 engine. So since It's a 3.7, dodge dakota. I have been buying parts for a 3.7 dodge dakota which means that it wasn't matching the fuel flow rate. But for some reason at some point there were 3.3 / 3.8 injectors installed and it's been running the whole time like that. I'm pretty much at the end of my rope with this thing but I am really hoping that someone might have some insight as to why a different version of injectors were installed. Thanks in advance for your thoughts.

 

If all 6 injectors were changed, the ECU was able to figure out that each bank was rich or lean and adjusted the injectors. It can only adjust each bank, not each injector one at a time as it's using O2 sensor data to figure that out. Now that you are mixing injectors, it can't figure it out what to do as the injectors would have a different flow rate for the given pulse width causing either a rich or lean on the bank and try to adjust, but that is enough to cause a misfire. I would start by putting in all matching injectors, preferably the ones designed for this engine. since you said that you had already done 2 injectors, get another 4 proper 3.7 injectors and put all matching ones in. The ECU should then figure out what's going on.

as for why the 3.3/3.8 injectors were installed, someone might have had them on the shelf and installed them. since they physically fit and have the same plug. They obviously worked for a while, until they didn't and you started having your issues.