No 8 volt supply from pcm

I had an intermittent no fire issue on a 97 Dakota once. It ended up being a bad ECU. Someone had leaned over the fender to work on the truck and put too much pressure on the connectors. They had craked the plastic housing that holds the harness connectors to the ECU and caused a bad connection. The customer would bring the truck into the shop and it would run fine, we'd give it back and the next week it would get towed in. Anyway, might be something to check.

so gue$$ stinks sure.... why do that.?
all it takes is a scan tool to find this.

first you need to learn ASD relay rules.
to start a jeep 1993 to NOW.
the ASD most close, cranking,does it?
and most stay closed cranking and NOT drop out in 3 seconds.
that means crank for 5 seconds and if the ASD drops. at 3.?
easy huh?
if it did DROP i can tell you the ECU will set DTC errors you failed to see because you did not scan it during those 5 seconds.

http://www.fixkick.com/Jeeps/ASD.html

first is fuses.
lets make a list. works on all jeeps 93+

1. battery changed. to 12.6vdc reseted.
2. keyon, CEL lamp glows, if not fuse blown to PCM (ECU)
3. engine cranks fast.
4. Asd realy pulls in and holds.
5. scan tool shows, what? BINGO. DTC errors, easy huh?
6. ok no DTC, errors, live for 5 seconds, cranking,so lost spark? must be bad coil or wired wrong. (change it 1 wire at a time?ooops)
7. coil dead, its not DTC caused, so if no DTC that means the PCM did not see Coil ignitor errors. to coil see? i bet its got TDC;s if not then i check the coil inputs. to be sure the PCM ignitor is firing the coil correctly with my scope, oops no scope.
8. if no scope you get to buy a new PCM. Wild guessing bad ignitor.
9. i use a Innova 3140 scan too that does 93-95 jeeps, for about $150 only about 1.5 hrs shop labor value. and is Investment grade tool, it would have saved you 3 parts, guessed already.

Check the ASD relay in under hood fuse/ relay box. ASD stands for automatic shut down relay. Powers up pcm ,fuel injectors and ignition system an O2sensor heaters .crank over the car an check for power at O2sensor heater fuse in the underhood fuse box ,no power means bad relay !

1994 Jeep, Cherokee?

check all EFI system fuse first with a meter.

that is ASD drop out.
all jeeps from 93 to now have ASD relays.

43 code (nice checking you did) is bad spark.
when the PCM sees bad spark it then shuts every thing down

http://www.fixkick.com/Jeeps/ASD.html

cause is bad ignitor or coil.
the big v8, with the funny locking throttle body... short.
that is true if you crank for 5 full seconds.
to see if CMP sensor fails too.
cmp cam sensor is in the distributor base.
the ignitor is in the PCM, and drives the coil directly.
i presume spark is dead directly at the coil terminal
and is dead the first 2 seconds cranking. right.
takes 2 person to test spark. one at key , 1 and coil
the PCM only allows 2 seconds for spark to happen
if it fails ,it kills the ASD relay.
making trouble shooting tad hard , for those that dont know jeep ASD issues.
if the 5.2L cmp and CKP sensors work right, the PCM then creates spark
it does this via and ignitor.
the coil can be bad, as can the rotor and cap. id replace any old cap and rotor, fast. if the coil tower terminal HV. has good spark.

read failure to start test here
http://www.jeep4x4center.com/knowledge-base/index.htm?utm_source=cj#service
chapter 8D-6

and page 8w-30-4 , coil schematic.
as you can see, the coil has 12vdc key on for 2 seconds.
cranking.
the PCM ground the minus coil pin.
this charges and fires the coil
the ignitor transistor is in the PCM on this car.
The PCM monitors this pin minus , and if it fails to pulse,
it knows the Coil is dead. and then shuts down EVERYTHING EFI wise.

that is how it works.
tricky yes,but true.

The dark green orange wire is voltage from the ASD relay. The other two wires are ground signals from the PCM. The PCM or computer takes the signals from the cam, crank, and temp sensors and decides when to fire the plugs and injectors.
You'll need a shop manual to get the test procedures for the coil and PCM. Its possible the cam and crank sensors are not in sync.

asd relay or fuse
camshaft not spinning
bad pcm
damaged wiring harness

Breeze, 4 cylinder: check fuse # 5 (20a), fuse #1 (10a), fuse # 10 (10a)- in the power distribution box. Check for power to the coil on the dark green wire with orange stripe. If power there, test the coil. If coil is good, suspect the cam position sensor or the crank position sensor.
Breeze, 6 cylinder: check fuse # 5 (20a), fuse # 10 (10a). Check for power to coil on the dark green wire with orange stripe. If no power to coil, try a new or known good Auto Shutdown Relay (in the power distribution center). If still no power to coil, may be a problem in wiring harness. If there is power to coil, and still no spark, test the coil. If coil is good, suspect the cam position sensor (in the distributor), or the crank position sensor. If all check good, may be a problem in the wiring or the pcm (computer).
Good luck.

When you have no spark at the coil,Then coil needs power from ignition which is supplied by the ASD relay,you also need a ground signal this is from the PCM,which recieves its input from the cranksensor, which is located,under the starter,Check for open fuses especially ignition fuse, and make sure the harness to the crank sensor is good,

first the cam sensor shouldn't be upside down from the 95. they both should be with the plug facing down. they 95 CAS has a different plug than the 99 CAS.
the 95 has round pins and the 99 has flat pins.

95-96

--------------------
97-99

-----------------------------
also the 95-96 relays are opposite the 97-99

95-96

------------------------
97-99

---------------------
besides that it could be the ecu. i also have heard of the locating pin on the intake cam shearing off, allowing the gear to turn with the timing belt without the actual camshaft spinning.

TRY UNPLUGGING DISTRIBUTOR PICKUP CONNECTOR AND SEE IF 8V SUPPLY RETURNS..IF NOT,TRY UNPLUGGING VEHICLE SPEED SENSOR IN TRANS..THESE SHARE THE 8V SUPPLY CIRCUIT TO CRANK SENSOR ONE OF THEM MAY BE SHORTED..THERE IS NO GROUND TO ASD RELAY BECAUSE THE PCM MUST SEE CAM AND CRANK SIGNALS TO GROUND THE ASD RELAY..I HOPE THIS HELPS