Pcm and alt shorted

[nate343]

HELLO FOLKS. I HAVE A 94 RANGER XLT 2.3L WITH A MANUAL TRANS. ABOUT 5 MONTHS AGO IT BEGAN TO HAVE AN INTERMITTENT STALL. ACTUALLY, MORE OF A BUCK/JERK THAN A STALL. IT WOULD LAST FOR A FRACTION OF A SECOND, THEN DISAPPEAR. NO CEL. JUST DEAD AND ALIVE AGAIN.

A BIT OF HISTORY:
I TESTED AND RETESTED MY SENSORS AND ACTUATORS. BOTH IN HOT AND COLD STATES. CHECKED MY GROUNDS. CHECKED FOR WIRING OPENS/SHORTS TO GROUND. EVERYTHING LOOKS GOOD. IDLE SEEMED TO BE AFFECTED BY WIGGLING THE PCM CONNECTOR. I TOOK THE CONNECTOR APART, CLEANED IT, CRIMPED THE TERMINATIONS, GREASED AND REASSEMBLED IT. WITH A TIMING LIGHT, I NOTICED A VERY INCONSISTENT FLASH. THE PLUGS ARE NEW AS ARE THE PLUG WIRES (MOTORCRAFT). MY ICM TESTED BAD AT THE LOCAL AUTO PARTS STORE. REPLACED IT WITH A NEW MOTORCRAFT - NO CHANGE. DPI WAS GONE - SHE STARTED WITH EITHER CP ALONE.
PRESENT:
PARASITIC DRAIN PRESENT. I'M HOPING MY INTERMITTENT PROBLEM HAS BECOME A FULL BLOWN FAILURE. I'VE FOUND TWO DRAINS SO FAR - ALTERNATOR AND PCM. WITH ONLY THE PCM FUSE IN THE UNDERHOOD BOX (ALL RELAYS AND FUSES REMOVED, FIREWALL CONNECTOR DISCONNECTED). THE PCM CASE SHOWS BATTERY VOLTAGE. THE POWER, AND CASE GROUNDS SHOW THE SAME. WITH THE PCM CONNECTED BUT NOT CONTACTING THE BODY, THERE IS NO DRAIN. WHEN I HAVE ONLY THE ALTERNATOR FUSE IN THE BOX. I GET DRAIN. THE ALT CASE SHOWS ABOUT 0.1V BELOW VBAT. I WENT TO NAPA, GOT A REMAN ALT, PLUGGED IN THE VOLTAGE REGULATOR - ONLY TO FIND THE SAME DRAIN. I'VE HEARD OF BAD ALTS OFF THE SHELF, BUT MY INEXPERIENCE IN ELECTRICAL ISSUES MAKES ME THINK I'M JUST TO DAFT TO KNOW WHAT'S GOING ON. NAPA REFUNDED MY MONEY, BUT I AM CONFUSED, FRUSTRATED AND DON'T KNOW WHICH ALT TO GET. CAN SOMEONE SUGGEST A QUALITY BRAND ALT.

SORRY FOR THE LONG POST. I'M JUST HOPING SOMEONE MAY HAVE SOME EXPERIENCE WITH THIS TYPE OF PCM/ALT PROBLEM. I WILL APPRECIATE ANY HELP!

 

[Tbars4]

...Don't type in CAPS...

...I had a similar problem with the buck and jerk on my 95 Ranger...

...I found the Solenoid Purge Valve wires were getting cut/grounded on my battery tray...This would happen on sharp turns or bumps but I could see how it would take out a pcm or alternator when it would kill/restart the motor each time...

 

[nate343]

Sorry about the caps. My caps lock sticks sometimes. My Ranger doesn't have a canister purge solenoid. I've checked every wire connecting to the PCM for opens and/or shorts to ground. I've done the same check at the sensors/actuators just to make sure I had the same results at both ends of the wires. Gave the harness and connectors a good wiggle while checking the continuity. The wiring appears to be in good shape. While investigating the drain through the PCM I unplugged the sensors and actuators thinking that one of them may be grounding a vref from the computer - no change. They all seem to be fine.

Right now, what really confuses me is the drain through the alt. My understanding is that the battery voltage applied through the ignition switch (I terminal) triggers a transistor in the voltage regulator to pass current from the A terminal feed (hot at all times w/15A fuse) through the voltage regulator and then the field coils. My original alt and the reman NAPA unit I got both flowed current with no voltage applied to the I terminal. In fact the ignition switch was not even in the vehicle. I checked for a short between the wires feeding the I and A terminals thinking that the hot at all times A wire was getting voltage to the I terminal and allowing the regulator to pass current. I couldn't find a short and verified that the A wire was the only one carrying battery voltage. Am I completely wrong about how the voltage regulator functions? I thought I was on top of the alt drain until the reman unit had the same "problem" as the original alt.