93 xj OBD 1 Code 11 Crank no start

[Akton]

Starting off,
Information on jeep Year 1993 (body) 1994 L6 4.0 engine, AX15 5 speed manual transmission I suspect is from the 93 body, suspect ECU is from 93 jeep (see later)
Model XJ base 4 door 4x4
Code 11 OBD1 (modules replaced CAM sensor and Crank position Sensor)

Symptoms and prior condition: Crank no start, Jeep was previously hard to start in the mornings [would crank but not run until battery light illuminated and turned off], power on and waiting 30 seconds usually remedied this. [Duration of these symptoms 2 years].
Summer 2023, destroyed clutch hydraulic line, so I serviced the transmission with a new slave cylinder and clutch kit. Since I was already down, new oil pan, rear main seal, and harmonic balancer seal replaced to fix oil leak, (now oil is only leaking from the valve cover...). While I was there I changed the oil pump. Spring of 2024 I changed the power steering pump to the WJ model which is much quieter.
Last fall (2024) my inspection plate was contacting the fly wheel upon shifting (post clutch change) this required removal of flywheel and reconditioning of the plate between motor and transmission. Upon the drive home with this noise the car died 40 feet from my house, coasted into driveway and proceeded to remove transmission and fix the plate. (it barely made contact)

Attempted repair/first start post transmission work. After assembly I forgot the CPS... We all know how fun that was to reinstall, but to my surprise no crank continued.
CPS was replaced, No start, So I bought a OBD1 scan tool (something I had put off for far too long). Code 11, missing signal from crank shaft position sensor or cam shaft position sensor.
Replaced distributor with new cam sensor. No start.
Upon looking up my symptoms a capacitor problem is known to exist for the ECU, Being into micro electronic repair, I replaced the three electrolytic 220 micro farad 25 V capacitors (upgraded to 35V (upgrading voltage is a good option as it lowers the stress on the capacitor, it has no electrical downsides other than cost/size)) and crank, no start, code 11. Upon removing some of the silicone sealant I found that the PCB was made in 1991 where the case which the silicone was poured was cast in January of 93, it might be a 94 but unsure.

I am looking for advice, (* I want to test the wiring harness (which is most certainly from the 93 frame), but I am not sure which signal wires to and from the ECU are on which pins, Specifically I hope someone knows where the 8V signal to the CPS and CAM come from, which ground they are supposed to use from the ECU as their reference, and most importantly which pins the return for CPS and CAM are supposed to be on) Without this knowledge I am unsure how to look for breaks or corrosion in the wiring harness.

Short of this I may have to test my luck buying a refurbished and programmed ECU off the web since MOPAR (according to my local dealer) has the ECU as a end of life product and neither can reprogram nor replace them. (I don't know if I believe the guy).

 

[Akton]

Tools needed 1 Volt meter with continuity mode, extra small diameter probes are nice as standard volt meter probes are hard to fit into CAM, CPS, and ECU/PCM connectors. Regular ones work, but they are finicky at best, a paperclip and alligator clamp can be very useful.
2 proper wiring schematics for your year of jeep (it may be compatable with a range of years for your model).
3 5/16 ratchet or driver to remove ECU/PCM plug
Find your jeeps connectors, common ground / voltage, and signal return. (depending on year of your jeep these will not be the same, but the process is the same).
After finding a pinout for the 93 xj wiring harness, I found common ground, reference ground, sense, and two different voltages are supplied. Many sensors have one common ground for all sensors and each sensor has a specific signal line to the PCM or ECU (I see it listed both ways).
CAM CPS and Speed sensors share common ground and common 5V source.
TPS shares the same ground and has a 8V source (other sensors are involved but not for engine startup).
Each sensor has a separate signal line to the ECU. With all sensors unplugged you can test both endpoints of the harness, separation of the Transmission/Transfer Case loom allows for all pins to be tested in the engine bay, The separated loom can be tested anywhere, but anywhere that is not under the jeep is my choice.

WITH POWER ON ECU/PCM REMOVED Volt meter in DC 9Volt battery mode.
With the PCM/ECU separated from the harness, and key in the on position the battery signal voltage to the ECU was exactly the voltage of the battery, (no voltage correction, this indicates the power source to the computer).
PCM/ECU input (battery) voltage 12.55V (normal). This should mean any voltage issues are either from the ECU/PCM or are from a short down stream.
CPS CAM and Speed sensors had 1.34V on CAM and CPS 0V on Speed (normally 5V) and the normally TPS was measuring 3.04V (8V normally).
Oddly enough 0V and no ground was found on the speed sensor, removing the wiring harness from the top of the engine loom isolated a short. (quick test for anyone in the future with code 11 is remove the transmission/transfer case harness connector in the engine bay, its a large 6 pin 3x2 deutsche connector)


WITH POWER OFF negative battery ground disconnected, Volt meter in continuity mode. Do not use volt meter in continuity mode with the battery connected or the car in the on key position. It can fry your volt meter.
CPS CAM and TPS wires to ECU (PCM) measured .4 ohm or less on signal ground and voltage from the PCM connector to the sensor connectors, No corrosion or shorted lines found.

WITH POWER ON ECU/PCM REMOVED volt meter in DC 9Volt battery mode.
Removal of transmission line (which in the manual transmission only supplies speed and Part time usage light for 4x4, and the sensors now read 5V & 8V where expected. Reconnecting all sensors except for those on the affected transmission loom and ECU/PCM, and we got engine start.

I am sourcing new connectors or at least ones that have insulation, (my speed sensor had all three lines with little to no insulation, the bad thing about having no oil leak, was that it exposed the cracked and corroded lines and shorted them). This damage was not visible due to the electrical tape on the end of the wire shielding. On the positives, I have backup parts, the new distributor sounds better, and with the capacitor modification their is no lazy first start up.

I will later upload the schematic with the highlighted diagram for affected sensors, I will also upload pictures of the modification to the ECU/PCM and the fix, what ever it will be for the affected loom.

 

[rtd16]

When you say 'removal of the transmission line' do you mean you just disconnected the harness at the transfer case? I'm asking because I am battling a separate starting issue and trying to eliminate possible causes. I had not thought about the trans/transfer case as a possible contributor

 

[Akton]

The wiring harness on the 93 jeep with a manual transmission has a connector on the upper engine harness near the hood at the passenger firewall, this isolates the speed sensor and the 4x4 lamp switch. This part of the wiring harness has connections that should illuminate the part time only cluster light, and the speed sensor. I checked several jeeps at a pull a part, until 92 its a speed cable not a sensor, after 95 the connector is a different type, and if it is a 2 wheel jeep it is obviously missing the 4x4 connector. This is not the only wire to the transmission as the reverse lamp is on a separate wire not part of this loom.

By removing this section of the wiring harness, my no start went away, so I pulled that line out and went through each wire in the loom, looking for breaks, or worn through insulation.

 

[Akton]

Starting with the wiring diagram, A scan of a document I printed out, the forum I pulled the original diagram for was for the 93 XJ specifically. Annotations and highlights are my own.

When I wrote transmission line above, I was referring to this section of the harness.
Also ignore the faded string on the engine connector, that was part of a pull line I put in the jeep to make installation easier next time (not to pull from it but to prevent the line from falling after I stick it back into the engine bay.

This was the problem. It may not look it, but the wires insulation was broken about 2 inches, and was corroded, After I fixed my oil leak, one trip through a puddle at the end of my street and the car died.
I believe the oil and dirt on the bottom was shielding the wires for some time, it was a pain to remove, this is after cleaning the connector.

After I split the loom, inspected all the wires, spliced in the new connector, I wrapped the interior wire with sections of heat shrink near the connectors, and used fabric loom tape on the wire bundles. After I used more of the loom tape to wrap the original plastic wire armor (Since it was better than the new stuff I could buy locally). Yes it will get dirty, but if it protects the wires, that's really all I am concerned with.

*please ignore my hand writing skills, I am studying to be a medical doctor, not a calligraphist.

Side note if your insulation is cracked at the connector but the wire is not corroded you can repair your connector, rather than replace.
You can with a small (1/16th flat head) screwdriver, remove the plastic part of the speed clip one stop catches on each pin twice, remove the individual wires from the rear of the speed connector, slide the rubber stopper down the wire, and you can heat shrink each wire, the rubber does fit over the heat shrink with some effort.