Code 15 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test
Failure). The voltage to the Keep Alive Memory (KAM) is missing (wiring problem)
or the KAM is bad. The KAM holds all of the settings that the computer "learns" as
it operates and all the stored error codes that are generated as a result of
something malfunctioning while the engine is running. Use a voltmeter to check
the voltage to the pin 1 on the computer - you should always have 12 volts. No
constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM is
bad and the computer is faulty.
If the computer has to "relearn" all the optimum settings every time it powers up,
the initial 5-30 minutes of operation may exhibit surges, poor low speed performance,
and rough idle.
Note that some aftermarket chips will cause code 15 to set. Remove the chip,
clear the codes and retest.
Before replacing the computer, remove the battery ground cable for about 20
minutes. This will clear all the codes. Retest after several days of running. If the 15
code is gone, then don't worry about it. If it is still there, then you get to do some
troubleshooting.
Wiring diagrams for the proper model years are next…
For 86 models see
http://www.autozone.com/images/cds/gif/large/0900823d80167158.gif
For 87 models see
http://www.autozone.com/images/cds/gif/large/0900823d8016715e.gif
For 88 models see
http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif
For 89-90 models see
http://www.autozone.com/images/cds/gif/large/0900823d8019595f.gif
For 91-93 models see
http://www.autozone.com/images/cds/gif/large/0900823d80195960.gif
See the following website for some help from Tmoss (diagram designer) & Stang&2
Birds (website host) for help on 88-95 wiring
http://www.veryuseful.com/mustang/tech/engine/
Diagram courtesy of Tmoss & Stang&2birds
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
Code 14 - Ignition pickup (PIP) was erratic – the hall effect sensor in the distributor is failing.
Bad sensor, bad wiring, dirty contacts. You have to press the distributor gear off the shaft to replace the sensor. The pip signal is used for ignition timing and fuel injector timing.
Code 18 - SPOUT out or wiring fault - look for short to ground in SPOUT wiring going
back to the computer. Possible bad TFI.
The SPOUT enables the distributor to advance the timing beyond the base setting. Without a
working SPOUT, you are locked down to the timing you set with the timing light.
Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check
vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring
and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid
and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always
energized any time the ignition switch is in the run position.
Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber
hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid
valve connects to one side of the canister. The other side of the canister connects to a rubber hose
that connects to a line that goes all the way back to the gas tank. There is an electrical connector
coming from the passenger side injector harness near #1 injector that plugs into the canister
solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide
some extra fuel.
It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps
the car from smelling like gasoline in a closed garage. So with all these good things and no bad
ones, why not hook it up & use it?