My neighbor has a 2005 Town & Country with the 3.3. It keeps blowing coil packs (they crack where the number 6 plug wire hooks up). He just changed the plugs/wires and it blew another coil pack.

We have the factory service manual, but he has not had time to go through the wiring diagram yet. Does anyone have any idea why it may be doing this?? Could a bad PCM cause it?? Is there a place to check where wires are more likely to get pinched and shorted??

Another thing is that he noticed that it shudders on the 1-2 shift. Also, it had blown the ASD fuse the first time it blew a coil pack. It has not blown that fuse since.

Any input will be greatly appreciated. Thanks in advance.

 

The problem is a short to ground in the harness or a bad coil driver in the PCM. That would keep power constantly on to the coil pack, causing it to burn up.

The coil pack receives power when the key is in the run position. The PCM toggles GROUND to the coil packs. So disconnect the connector to the coil pack. Connect a computer safe test light to battery + and to the ground wire (coil driver) in that coil pack connector. Crank the engine. The light should flash each time the PCM provides ground. If the light stays on with no flashing, you've got a short to ground. If it doesn't flash at all, you've got either an open on that driver wire, or a bad PCM--in that order.

One way to shorten up the testing process is to to check the driver for that coil pack directly at the PCM. Get a wiring diagram and connector pin out and do the same test at the PCM. If you're getting flashing, then the PCM is good and the problem is in the harness. You can either track down the open/short, or abandon the old wire and run a new one.

 

Okay. Tested at the coil pack connector and the light stays steady on that coil control wire (the other two coil control wires flash).

I then disconnected the connector at the PCM and did a ground loop test from each end of that control wire (hooked my multi meter up to the negative on the battery, then probed each end of Coil Control No. 3 wire). There was no indication of a short (correct me if this is not the proper method to verify a shorted wire).

So, if my diagnosis is correct (using your excellent test method), then I think it is a bad PCM. Let me know if you think this is correct.

 

Inspect the harness. Make sure you don't have a melted harness. You could also have a damaged harness from rubbing against the transmission.

 

Only thing I would add is to jostle the wire harness around as you check it for a short to ground. As DG says inspect the harness to see if it may be chaffed and close enough to structure to short to ground. If all is good then start hunting for a PCM. They can be had for $150 on the web reprogrammed and with a lifetime guarantee. If you head to a junkyard just make sure the PCM you get has the same part number and came from a van having the same security system set up or you can open a big can of worms.

 

My neighbor ordered a replacement PCM. When it arrived, we checked it for ground pulsing before hooking it up to the coil pack. The replacement was not pulsing the number 2 coil control circuit, so we let the company know. They sent out another replacement PCM. I got it installed tonight and it pulsed on all 3 grounds at the coil pack connector.

We hooked up the coil pack and it fired right up and was running smooth. He is going to drive it around quite a bit to be sure that it is okay, but I think it will be fine. The replacement PCM was $199 and has a lifetime warranty if you send your old one back within 14 days. If this one goes bad, they do an advance replacement on them, so your vehicle can still be driven until the new part arrives.

 

Good news. Sounds like you nailed it. Congrats.