Cylinder 4 Coil Fault - P2311 / P0304 / Replacement PCM

Trainmaster said:

The overflow nipple on the 3.7 coolant reservoir broke and flooded my engine bay. A few months after the repair, I was getting a P0304 #4 misfire with a P2311 code for a bad coil. I removed the coil and found it wet. It was shorting out for quite awhile. So I replaced the coil and plug and dried things out.

The miss didn't go away. Still a #4 miss and coil code. I moved the new coil and plug to another cylinder but the miss didn't follow it. Still a miss on #4.

I checked continuity on the two leads to the #4 coil. One lead is always hot (+12) when the ignition is on. The other should pulsate a ground from the PCM (computer's) #3 pin on its second-from-rear connector. There was no pulsating ground on that wire, though there was conductivity between the computer and the coil connector. I also checked each wire to ground and found nothing shorting to ground.

The PCM Computer on my 2005 has part number 56044576AO. The "AO" is just a date code and doesn't matter. It obviously lost its #4 coil output from being shorted so long.

Ebay has several sellers who will furnish a new PCM programmed to your VIN and mileage. I ordered one and got the wrong part number sent to me. Lots of these guys sell garbage. Sent it back and ordered one from a different dealer (Shifting Gears Auto on ebay) for $129. Plugged in the new computer and the truck runs flawlessly.

Just wanted to share this experience and hope it can help others.

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Trainmaster said:

I'm writing from memory here as the transmission blew later and I no longer have the car.

I recall that it is the ground to each coil that is pulsed by the PCM. I found a test light more usable than a meter, since these digital meters have delayed readings. If you ground one lead of your light, you should have positive at one coil lead with the ignition turned to run.

With the motor running, you should get a dim (maybe 6V?) flickering "flashing" lamp on the other lead if the test light is on the battery's positive. Try that on a good coil's wire and you'll see what you should get. If you're not getting it, you have either a bad wire to the PCM or a bad PCM.

You can check the continuity of the coil's wires with an ohm meter. Check between the coil end and the proper pin on the PCM plug. I then I checked between each wire and ground.

Good luck. Sounds like your problem's the same as mine.

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Trainmaster said:

Don't be too crazy about checking the wiring. We always hope that's the problem but it usually isn't.

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