Help much appreciated.. I have a 1993 FORD ranger 4.0 i am having a problem with coil pack blowing(i know it is blown cause when try to crank it ,it smokes and when i take it off there is a hole in coil pack) the wires are hooked up correctly. Have put three brand new ones on all do the same (getting expensive) The last one i put one it ran for at least 15 minutes then blew. I am not able to pull codes truck is undriveable witout coil pack working. Was wondering what to check please help i hate to see my FORD not on the road. I would rather not take it to a ford tech. any advice or knowledge about this situation will be appreciated!!

 

Well, you either have a bad PCM which is sending too much voltage to the coil, faulty wiring such as a short to ground in the coil wire circuit including a plug wire grounded to a piece of metal. Also, I'd pull the plugs and make sure none of them are broken. When the coil fires it's looking to have a certain amount of resistance in the ignition system and if it sees 0 resistance to ground it could very well be backfeeding and killing your coil. But I have seen a bad PCM do it the most. I make no promises without seeing the vehicle though, that's just my best idea of what to look for.

 

The only things that I can think of right off that could cause the coil pack to smoke would be:
1. A short in one of the three primary wires between the coil and the ignition control module.
2. A defective ignition control module.
3. An open circuit in the secondary (bad plug wire causing arc through internally in the coil secondary).
4. A defective coil pack (internally shorted primary).

 

Pull the primary connector off the coilpack (4 wire connector) With the ignition key on (run position), with your meter in voltage mode, meaure the
voltage on all 4 wires, one of them should be 12V. After finding the 12V terminal, but your meter in resistance (OHMS) mode, and measure the resistance on each of the other 3 wires. When you measure the resistance,
have your meter negative lead on GROUND. The coil drivers are open collector, and if they are ok, you should measure a high resistance.

 

First of all thanks for reply, where would the PCM be located on my ranger cause i have found the ignition module(EDIS) is that the same thing?? IN a manual i have it shows the PCM on the fire wall of the truck my 93 ranger or my 94 ranger neither one has this on the firwall where it shows it should be?

 

I have cut the two power wires to the coil pack and put some fuses on them then tried out new coil pack and it still blew it . What size fuses would be the best to put in there?

 

Did you pull the primary connector and do the measurements I suggested?

And to John, the PCM DOES NOT provide voltage to the coilpack, it has open collector drivers that provide the GROUND path (pulsed) to the primary of the coil.
Now, if one of the drivers are shorted, this would create a high current condition.

 

Here is the wiring diagram for your coil. Voltage IS supplied to your coil from the PCM power relay, and the coils are grounded through your ignition control module. If the 12 volt feed is good, and your base ignition system is good, the best bet is to replace the Ignition Control Module.

 

John, the PCM RELAY DOES NOT supply 12V to the coilpack!! 12V for the coilpack comes from the ignition switch, which also powers the coil to pick the PCM relay!!!!

Matter of fact, if you understood how a diode worked, you would see that the diode connected to the PCM relay in the schematic would be reverse biased to block
current flow from the PCM relay, but will pass current from the ignition switch into the PCM relay (coil).