need help with fuse 20 in power dist box, details below


electron1130
07-22-2011, 05:10 PM
I could really use some help. Fuse 20 (15A) pops when the pcm harness is attatched but does not when removed. I ohmed out all the wires on the harness and i have two wires that are suspect. One goes to the MAF sensor. Does anyone know if one of the wires to the MAF be grounded.

12Ounce
07-22-2011, 05:19 PM
Model year? Engine size?

wiswind
07-22-2011, 10:41 PM
The electrical diagram for my '96 does not seem to line up with what you are saying....so it will not be of much help.
In the '96 fuse 20 is a different value and power goes INTO it only with the ignition key in the start or run position.

Also, for the '96, fuses in the passenger compartment "IP" fuse panel, located under the dashboard on the driver's side are numbered.
The fuses in the power distribution box in the engine compartment are lettered (A, B, C)

If you can post your year and what engine you have (3.8L or 3.0L) it will help as someone with that year can look at their diagram.
1999 was a major change year, so anything newer than 1998 will be much different than my 1996 information.

olopezm
07-23-2011, 01:09 AM
Welcome to the forum buddy!

If you post the year and engine of your windstar I'll be glad to upload any diagram you need.

Oscar.

electron1130
07-24-2011, 06:15 AM
Its an 02 windstar and has the 3.8. And thank you so much

olopezm
07-24-2011, 06:54 PM
You're welcome!

That fuse has the Ref Voltage for several engine and transmission sensors, and the cooling fans. You'll have to disconnect all of them and reconnect one by one to see which one is the cause.

I would suspect the cooling fans or relays first as these are the one that need the most current when bad, other circuits would only stop operating...

Oscar.

electron1130
07-25-2011, 10:34 AM
Ok. The wire i was talking about is supposed to be grounded. The only other wire that is 0 ohms to ground is pin40 on the harness. It goes to the fuel pump and does not look like it should touch ground.

Let me just give u a background of what is going on. The van started dying when i would push the gas pedal, i knew the battery was going bad so i replaced it. Then i replaced the alternator because it was bad. For a while the speed guage was jumping around then a day after i replaced the alternator all the guages started going crazy, then it wouldnt even try to crank and a few different fuses were blowing. I removed the front electronics module and it had a few components that were burned up so i got one from a junkyard. The fuse to the dash cluster was still blowing so i removed that and that fuse quit blowing, the board to the dash cluster has three diodes that look slightly burned and smell burned. But the fuse 20 is still burning up and that powers a bunch of the powertrain stuff. How can all these things go bad at the same time? And im wondering if changing the front electronics module is going to make it so i cant start it because that vans key has a chip in it that has to match some theft protection programming.

12Ounce
07-25-2011, 01:50 PM
As Olopezm wrote: disconnect ALL the loads on that fuse ... and reconnect them one-by-one until you know the culprit.

olopezm
07-25-2011, 06:43 PM
Woah wait!

I didn't say they are all bad, I was only mentioning that if the sensors would be bad they would only stop working unlike the cooling fans which will draw a bigger amount of current and blow the fuse.

12Ounce has explained what I meant to say in my older post.

Oscar.

olopezm
07-25-2011, 07:11 PM
I forgot to ask where did you get the alternator from?

Some cheap aftermarket's can be bad out of the box and a bad diode in it can cuase you gauges to go wild. Measure AC voltage with a DMM accross the battery terminals when you get the engine to run. If you see any value you might have a bad alternator.

electron1130
07-26-2011, 04:35 PM
i was suspicious that the new alternator was bad. it was a rebuild from advance auto. i measured the voltage during the period that it was still running and was getting 13.2v at idle then then would jump up to 14.0v when revving the engine. seemed to me like the voltage regulator in the alternator should make it so the volts don't change.

olopezm
07-26-2011, 07:09 PM
You are correct, the alternator should show around 14.6 volts at idle.

I really suspect part, if not all, of your problem is the alternator, have it tested at two different shops so you can compare. Also if you could swap it with a good alternator would be great.

I don't want to think the bad alternator toasted other components in your van.

Oscar.

electron1130
07-31-2011, 04:44 PM
Update: the problem causing fuse 20 (distribution box in engine compartment) ended up being the "powertrain control module" (PCM). after unplugging every valve, switch, and sensor coming off the pcm and the fuse was still blowing, i figured it had to be the module. If anyone needs to know how to get the pcm out email me, ethanaw@att.net.

12Ounce
07-31-2011, 07:18 PM
CAREFUL!

The PCM is very robust. I would be very slow to assume it is the "root" problem. .... and when replaced, may require reprogramming with equipment only at Ford dealer.

IIRM, the PCM is removable with two small screws .... just under the RH hood hinge.

electron1130
08-17-2011, 11:01 PM
Van is fixed! I had to replace my FEM (front electronics module), PCM (powertrain control module), and the guage cluster. The alternator i bought from advance auto was bad. I made the mistake of trying to check if the new alternator was bad by unhooking the positive cable to the battery. I drove the van around the block after removing the cable and thats when the bad alternator fried the modules and guage cluster. DO NOT CHECK YOUR ALTERNATOR BY REMOVING BATTERY CABLE!! After replacing the modules i had to have them reprogrammed by the dealer because the anti-theft no longer matched the key.

olopezm
08-17-2011, 11:28 PM
I'm glad you fixed your problem. Thanks for letting the forum know what was the cause of it.

For future reference

Disconnecting the battery while the engine is running used to be a good measure for older vehicles but with all the electronics involved in PCM controlled vehicles it's a DEFINITELY BAD IDEA.

Why is that?

Because the load on the system is being sensed to properly adjust the voltage regulator duty cycle in order to provide the optimal/correct amount of current form the alternator. If you disconnect the battery the system will sense a huge load (open circuit/high impedance condition) and will activate the regulator at 100% duty cycle, since the current has to go somewhere, all of the electric/electronic circuits will be affected (mostly toasted) because of the high current being fed.

Regards,

Oscar.

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