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Unread 10-10-2014, 11:04 AM   #1
mylogylo
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1994 YJ Wrangler 
 
Join Date: May 2007
Location: Dillon, Colorado
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Voltage regulator test

Hey Guys! Happy Friday! Is there a way to test the voltage regulator on the ECU or whatever its called?

I cannot figure out why my heep is overcharging all the time. I cleaned up a mess of wires, cleaned up the battery terminals, has a new alternator upgraded alternator, etc....Still over fifteen volts with a meter on the battery.

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Unread 10-10-2014, 12:49 PM   #2
JWELK
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You need an oscilloscope and the ability to use it. In the old, old days the generator was on or off, alternators used a varying voltage on the field to adjust the output. Now they use computer generated data to send a pulsed signal to the field. So how much over 15 volts is it? On my 95 the field output is a Dark Green wire on Pin 20 of the Powertrain Control Module.
That being said the input to the ECU could be low, resulting in the ECU giving a higher than normal charge rate. Check the following Pins on the PCM Pin3, 12 volts in; Pin5, Ground; Pin6 5Volts out; Pin7 8Volts out.

Again this is for a 95, but they might be similar. Pins 3 and 5 being the most important. If either is corroded it will generate a bad signal, same with Pin 5 being poorly grounded.

Regards,

Jim W
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Unread 10-10-2014, 01:14 PM   #3
Que89YJ
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Same setup exactly what he said x2. If that is putting out over 15 you need to fix what is going on immediately. That is getting into the area of enough voltage to cause a battery to boil and or explode.
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Unread 10-10-2014, 02:01 PM   #4
mylogylo
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Thanks a ton. I couldn't find much on the google. I was told previously on another thread to fix the voltage issue asap and really hoped cleaning up all my wiring hacks from the last fifteen years, replacing the alternator, and vacuuming the seats would fix it.
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Unread 10-10-2014, 04:48 PM   #5
Que89YJ
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What is your voltage exactly?
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Unread 10-10-2014, 06:14 PM   #6
mylogylo
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Between 15.1-15.3 volts at idle and it climbs a bunch if I rev the engine. I only got it to 2K RPMs but that brought it up to 15.5ish. Thats with a meter at the battery. Battery with the engine off is 12.8ish.
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Unread 10-10-2014, 09:52 PM   #7
Que89YJ
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You are full fielding the alternator. That is very very bad. Do not drive it until it's fixerd. Do what he said.
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Unread 10-11-2014, 10:12 AM   #8
mylogylo
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Alright, couple things...i have a Jet chip, I cannot remove it for the life of me. I was kinda hoping maybe it just had issues and once I removed it things would start working normal again. Should I spend a bunch of time and risk breaking it or just leave it?

Is there a difference between PCM and ECU? or are they the same thing?

To test everything I am just removing the big harness from the ECU and testing at the connections in the harness right? I got a little over 12 volts at pin 3, and pin 5 definitely is grounded. I got nothing at all on pin 6 or 7.
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Unread 10-11-2014, 06:39 PM   #9
Que89YJ
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You need to check pin 20 to ground. You have the right power. PCM/ECU is the same.
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Unread 10-11-2014, 10:15 PM   #10
mylogylo
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Alright, the battery with the engine off was at 12.56 volts. I had it retested today as well and it is fine. Alternator (grand cherokee 136amp) has about 50 miles on it. It was overcharging before I replaced the alternator. I also spent a few days rewiring and cleaning up every accessory I've installed...fan, H4 headlights, foglights, reverse cheapo fog lights. Everything is done right as far as I know

I unplugged the harness from the ECU and tested the sockets.

Pin 3 - 12.56 volts
Pin 5 - Ground
Pin 6 - No reading
Pin 7 - No reading
Pin 20 - Ground

Looking at some other threads...I need to do this with the jeep running huh?
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Unread 10-12-2014, 12:49 PM   #11
mylogylo
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I grounded pin 20 with the jeep running and the voltage at the battery shot up to at least 18 volts. The battery really didn't like that at all, it spit out most of the water that was inside.
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Unread 10-12-2014, 08:19 PM   #12
Que89YJ
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You should never do that more than a few seconds. Full fielding by grounding pin 20 is a good test but must be done with caution. You checked pin 20 to ground with the key off and battery disconnected? If not, repeat and post results.
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Unread 10-15-2014, 11:23 AM   #13
mylogylo
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Hey Que, sorry for not responding sooner. I had to run out of town for a few days but will jump into it again early next week. When I grounded pin 20 it was super quick, just enough to register on the meter. I checked pin 20 with the jeep running though...I will do it again with the battery disconnected and the key off. Thanks for all your help. Nobody around me has the computers so that will be tricky if I do need to get one.
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