I’ve had a misfire condition on my '01 Dakota for months. It idles a little low, but it’s done that for a decade.
The codes I’m getting are 300, 301, 303 and 305. Multiple misfires, cylinder 1 misfire, cylinder 3 misfire, cylinder 5 misfire.
The most obvious thing to check was that I had mixed up the spark plug wires, but I’ve triple checked that. I’ve replaced the spark plugs, wires, distributor cap and rotor. I’ve tested the new wires for resistance. I haven’t changed the coil, because if the coil were bad, the problem would not discriminate to one side of the engine. As far as I can tell, there is no problem with spark.
I did not replace the fuel injectors, but I moved the injectors from the misfiring cylinders to the opposite side to see if the misfire moved with them. No luck. So it doesn’t seem to be a fuel problem.
I’ve done a compression check on each cylinder. The #1 and #2 cylinders were each slightly lower pressure than #3-6, but within 10%. #3-6 were all within a pound or so of each other.
I haven’t done a back pressure check because I don’t have, or especially want to buy, an expensive gauge to test one thing. There’s no codes coming from the cats, so I doubt there’s a problem with them. There are also no visible leaks to the exhaust at any point.
As a final resort, I bought a refurbished PCM. After installation, the codes went away long enough to get the truck inspected, but about 150 miles later the codes are back.
Dear old dad suggested checking the fuel rail to see if, somehow, that side of the rail is clogged or restricted. I’ll check it, although it seems unlikely that the 1/4" rail would clog before the pinhole sized opening in the fuel injector.
Beyond that, I’m out of ideas. Despite my DIY or die attitude, I would take it to a shop at this point… Except I haven’t been able to find a mechanic who seemed to have even as much knowledge about ignition systems as I do, let alone more. I need a diagnostician, and all I can find are parts changers.
So I’m really hoping that A, my guardian angel reads the cartalk forums, or B, that somebody here has an idea I hadn’t thought of.
Thanks in advance!