Topic: Cranks but no ignition: no power to PCM

[Eucalypta]

Hello guys, I must admit...I went over to the dark side.
Swapped my 2.5L + AX5 with a 4.0L with AW4.

It ran great: did some testing on highway and in terrain (mud): what a joy 

Then the Gremlin came in: first my generator worn out: gave to little power. Swapped it for a rebuilt model but after some playing in the mud it gave over 19V power output: boiled my battery.
I swapped it for a new generator and it did fine however....
- my AW4 did not gear-up/down: drove about 2 km to wash my car after the mudbath it been in
- checked the fuses: autom trans fuse blown
- put in a new fuse and now the car cranks, everything (radio, lights, ...) works fine but no ignition.
- put it back in former state when I was still able to drive it (took out the autm trans fuse): still same problem
- check-engine light and battery light do not light up when contact is put to run/start
- diagnose computer does not see the PCM
- other PCM's connected: still same problem
- fuses checked out ok (both in PDC and onboard fuse box)
- could be the ignition switch but seems bit unlikely

Any pointers (apart from telling me it is my punishment for turning my back to the wonderful L4)?

[Jeffy]

By generator, do you mean alternator?  Did you have the alternator(s) tested?  The PCM regulates the voltage.  Did you check the PCM for stored codes?

Since you did the swap, everything should be fairly fresh in your memory.  I'd check the wiring.  Make sure all the wiring has connectivity.  Also make sure you have all your grounds.  Weird things can happen when there isn't a ground and it needs one.

[Eucalypta]

Yep: alternator.
If the Alternator is defect: the PCM should still be accessible to the OBD-tool.

There seems to be two different problems occuring at the same time (It's a Jeep thing)
Problem 1: worn out alternator was swapped by a defect alternator with broken ancor resulting in maximum voltage (>21V)
Swapped with a brand new alternator: voltage from alternator regulated to 14,0 V => OK 

Problem 2: I drove the Jeep (with new alternator) to my house to have it washed. I used (carefully) a high pressure cleaner to get rid of most of the dirt.
Also on the interior. It seems this habbit brought up the problem:
- power to PCM (no 9): 2,3 V 
- connector on ignition switch loose: when I push the connector firmly on the switch and turn on to "run": nothing: fuse "Ignition" in the PDC AND fuse "dome"  in onboard fusebox burn out.
- connector inspected: corroded. cleaned the connector, connected it to the switch, replaced the fuses, turn ignition to "run": power tot PDC 12,3 V 
- Motor starts and runs: checked codes on PCM: no codes, all readings withing specs.

This afternoon I will make a testdrive to see if the AW4 will work like it is suppose to. Hope the high voltage did not damage the transmission computer. 

Lessons learned:
- Do not assume that the problem is cause by the former repair (yet do trace your steps)
- Do not believe labelling on fuses ("dome" is also used for the PCM)
- I will NOT use the high pressure cleaner on the interior again (and very carefully on the exterior)
- Test replacement parts near my house before wheeling in terrain

Thnx guys!

[Jeffy]

One way to protect electronics like the alternator and PCM when washing is to cover them with a plastic bag.

[Eucalypta]

@Jeffy 

Next problem, maybe same cause there for in same thread:

The car runs but the AW4 does still not shift; Fuse of the AW4 keeps burning through.
I disconnected the transmission from the TCU: still burning through
Disconnected the TCU from the harness: fuses stays alive, even then switching the comfort/power button.
Opened the TCU: looks like new inside: no damages or brun marks.

Who has an idea of where to start looking?
Remember: it all started with my alternator putting out too much voltage.

[Eucalypta]

Again, a bit closer to the sollution.
Took the TCU apart today. At first sight, no damage anywhere.
Measuring resistance between feed and ground: almost none.
Looking at the back of the circuit board: heat damage is visible: one conduction lead is burned away probably components are damaged as well.
Tomorrow another TCU comes in. Let's hope that solves my problem.

[VA_YJ]

You should consider getting a Cherokee manual appropriate for the drivetrain that you swapped in if you don't already have one.  Also, the NAXJA website has tons of info on the XJ drivetrain.  Good luck!

[Eucalypta]

Put in the new TCU: all problems solved.
Although the TCU looked as new; the diodes were all burned due to the high voltage from malfunctioning alternator.
Runs great now.

VA_YJ: thnx; I like the AW4 for offroading better than an AX15. I just got into trouble with the bad alternator.