New to the forum and have a question regarding several DTCs and a CEL on a friend's 2002 Dakota SXT 3.9L manual 5 speed with 186k miles.


I ran an automated diagnostic scan using a very detailed and capable Autel Maxisys Elite that I recently purchased to work on cars for friends, family, and on my own vehicles. After running the scan, here is the readout with the information setting off the CEL (wish I could share a screenshot or diag report, but have not figured out how to print from Maxisys yet):


PCM - Powertrain Module (codes all show active as opposed to stored)

P0455 Evaporative Emission (EVAP) leak monitor large leak detected (Active)

P0203 Injector 3 control circuit (Active)

P0201 Injector 1 control circuit (Active)

P0301 Cylinder 1 misfire (Active)


I re-ran the diag scan today after he brought his truck back for a check of current issues. None of the injector control circuit DTCs showed up, but the P0301 cylinder misfire was present. However, I checked all the injectors for voltage, ran a test on the coil (distributor in this case), and also checked current of the O2 sensors as well as performed a heated O2 sensor test. Everything seemed in order as far as data falling within the realm of proper function. I do hear a distinct hissing coming from the front of the engine, which could indicate the EVAP leak. However, I'm not certain how to track that down. I then cleared the DTCs and drove it over 20 miles on back roads, highway, and stop-and-go areas. The CEL did not come back on. The owner stated that he has reset the CEL a few times and it takes awhile to come back on. At this point, I'm lost as to what this could be. The only part of the spark cycle we have not changed out is the distributor cap and rotor. The engine has new plugs, new plug wires, and shows no signs of burn or deteriorating wiring on any of the fuel injectors or O2 sensors.


Hope someone can help me find the issue.

 

Wouldn't hurt to have a look at the cap, terminals, and plug wires. Dirty/corroded/fouled terminals in the cap can give you a fun intermittent problem.

 

Definitely true! Took the old cap and rotor off today to replace with a new unit. The contacts on the old cap were very corroded and the rotor tip was very worn. The cap and rotor had about 30k miles on them and were way past replacing.

 

I had the truck back at my shop for about 4 hours today, so I concentrated on several areas of concern. First, I replaced the distributor cap and rotor with a new unit. Then, I pulled plug 1 and looked it over. Definitely was already white on the terminal, indicating the cylinder running hot. The owner had just replaced plugs and plug wires about 2k miles ago. Then I checked cylinder 1 with a scope camera to see if the valves looked burned. Did not see any indication of a lean condition, and in fact, the owner has been using a cleaning agent. So, the valves looked great. After re-installing the plug and wire, I decided to investigate the #1 and #3 injectors. Once the were removed, I looked for any build up, then tested the impedance (ohms) with my multimeter. Both were at 13 Ohms, so I tested #5 on the same rail and got 13.8 Ohms, which is in tolerance. After cleaning them up a bit, I decided to swap #1 and #5 to see if that would clear up the cylinder 1 misfire DTC (P0301). I cleared the PCM codes and the CEL did not illuminate during my test drive. However, the vehicle is idling with a slight hesitation; not smoothly at all. It drives fine and does not hesitate during throttle application. I'm having my friend drive the truck tonight and tomorrow to work to let me know if the CEL comes back. I predict it will since I still believe it's a faulty O2 sensor on the driver's side (bank 1). It's not going to hurt to replace both the pre-cat and after-cat O2 sensors, so that's our next step.

 

If the PCM isn't whining about the rear O2s, or cat efficiency, I would skip the rear O2s, just do the fronts. The rears are basically just monitors in any event.

 

That's a good idea. I'll get the manifold bank 1 and 2 O2s, then change out the after-cat ones if needed. Thanks for the idea.