Yo,
I overwrote;
EEC IV PCM Removal up to & include 87- 91 COMPENDIUM;
"
To remove it first disconnect battery & get use 10 mm socket to unbolt the wiring harness "connector from inside the engine bay. Then pull plastic kick panel from inside cab & remove the retainer clip Remove it by lifting rear slightly & wiggling it out of the "pocket" ... the firewall rubber gasket will have a pretty good grip on the connector so it will take some persuasion to free. "
"...Remove driver's inside kick panel adjacent to pedals. It comes out through cabin." by Seattle FSB;
"Should be one small metal ***** holding it. Just slide it out, but be careful w/ gasket for firewall. Don't mess it up, you can reuse it." by Darth_ted_82
"You have to unplug it under the hood very low on the fire wall (10 mm socket)."
Hhere are some EEC IV PCM KILLER perpetrators and other causes:
Smell around the PCM. If it smells like dead fish, it's bad.
Look for PCM printed circuit board burn marks around leaking capacitors, resistors.
View attachment 182797
For example, see Old leaky capacitors in
swapped EEC and no more codes by jowens1126
Water damage from cowl leaks, ESPECIALLY if you you have wet carpet or mat near driver kick panel; or on PCM Connector due to a bad hood seal near cowl panel, viewable with hood up.
Corrosion or damage due to moisture is one of the main reasons for failure. Corrosion can enter through the wiring harness and moisture can enter by a failure in the seals in the PCM itself. This happens over a period of time (5 to 10 years) due to exposure to the elements.
The alternator could be generating an AC voltage spike due to bad diode(s) or supply Voltage
View attachment 182796
Overloads.
I recommend bench-testing the alternator for voltage output and AC voltage ripple.
Thermal stress due to excessive heat and excessive vibration that causes sensitive parts to fail.
Bronco was jump started on reverse polarity.
Connector pin damage or corrosion,
Other internals:
broken tracks,
cold solder joints,
short circuit,
thermal stress due to excessive heat and excessive vibration that causes sensitive parts to fail,
Overheated PC,.
Bad Intel 8061 chip or bad Intel 8361 memory chip,
Bad Internal Voltage Regulator, see
Wayback Machine by absent member Fireguy50 (Ryan M)