Fuel vapor purge solenoid vacuum circuit. I had a misfire on cyl 1,3,5 for about a 1 1/2 years. Tried all the things others did. I replaced my fuel filter/regulator on the fuel pump assembly with an airtex which happened to not seal good in the grommet like the original. Drove the truck for a week with no codes. Replaced the fuel pump assembly and P0300,P0301,P0303,P0305 came back. I disconnected the vapor line coming from the charcoal canister underneath going to the purge solenoid at the firewall, and have had no CEL or codes for two weeks now. I believe that an excessive vacuum was being pulled on the tank and was interfering with fuel delivery on bank one. I am not certain if the purge solenoid is at fault, or if the charcoal canister vent hose is restricted. I can tell you that this does work, as long as your truck does not have a leak detection pump in the EVAP system. Hopefully, I will get a chance to diagnose exactly what in this EVAP vacuum circuit is causing the problem. Maybe one of you other guys can beat me to it and post your findings.

 

I had a chance to pull of charcoal canister today. Three hoses connect to it. Hose to tank is fine. Can blow into tank hose pressure blows back. Vent hose from canister to back of engine is clear. Hose from canister to purge solenoid is clear. The canister itself appears to be functioning properly. So that leaves the purge solenoid. This is a $38 part at autozone and will be replaced in a day or two. Change the purge solenoid if you have P0300,P0301,P0303,P0305 misfire codes on cyl. 1, 3,and 5.

 

No more CEL for p0300,p0301,p0303,p0305.(also known as bank 1)

 

Hey , thanks for up dateing this ! Fought with the very same CEL problems for awhile now , i recently changed to the standard distibuter cap (aluminum towers) and rotor instead of the heavy duty (brass tower) distributer cap and rotor that i usually buy from o-reilys auto parts , and all the codes but one quit showing up for now , still have a po305 every now and then ,,, on that purge solenoid you got , just curious about what ohm reading do you get across the terminals from the old one compared to the new one , have you checked by chance ? can you tell that the new one is working as compared to the old one ?

 

A couple of years ago I could hear a ticking noise in the cab. I thought it was the distributor, but as it turns out it was the worn out canister purge solenoid. After replacing it, it is quieter than the old one. I never ohmed it or the new one. Clear your codes with an obd 2 scanner, and unplug the vacuum line coming from the gas tank going to the purge solenoid. Drive the truck like this for at least 2 key starts or longer(days-weeks) and no misfire codes should show up if it is indeed the solenoid causing the problem. My truck gave the p0300, and all misfires were on bank 1. Sometimes it was just one cylinder, other times a couple of cylinders, or all three. This will save you some money verifying that it is defective.

 

Bumping this old thread back up....

Anyone else try this? Rather than disconnecting the vacuum line, could I not just unlog the purge solenoid harness and have the same effect of bypassing the purge system?

 

I recently purchased a 1997 Dakota with a 3.9L V-6 and shortly after started having similar intermittent misfire issues (including the P0300, P0303, P0305 codes). I checked the purge solenoid valve, and while I found and fixed some vacuum leaks, the problem didn't go away. Replaced the distributer coil sensor and ignition coil, still didn't fix it. In my case, the misfire happened consistently after warm up, so I replaced the upstream and downstream O2 sensors. It misfired again after replacing them, but afterwards it seems to have gone away, so maybe it took the PCM/ECU a bit to adjust to the new sensors.

Just wanted to share in case someone else keeping these old Dakotas alive happens to have a similar problem. I was thankful to find these old posts to give me a starting point!