1996 4.0L 2wd Automatic
Recently replaced distributor, replaced Crankshaft Position Sensor with OEM 3 years ago.
New battery 1 month ago

Vehicle has no running issues. Have used as daily driver since I bought it 20 years ago. Has 196000 miles.

This am, would turn over, wouldn't start.

Cleaned grounds, checked fuses, both under dash and under hood. Swapped relays around, no difference

Tried OBDll BT Adapter with Torque App that I have used for 5 years and now won't connect to ecu. States either ignition is off, or adapter is bad. Adapter functions on other household vehicle.

Tested for voltage on cam sensor, cps, and temp sensor, no voltage, also no fuel pump hum when turning on ignition.

No spark to plugs when cranking.

I keep replacement parts as they are getting harder to find, I swapped the cam sensor out with new OEM. No difference.

I unplugged the cps, tried to reconnect OBDll, would not connect. Plugged in new OEM cps, though did not install, no difference.

Disconnected battery and reset ecu, no difference.

I have searched under "no power to ecu,cam sensor, cps" and found nothing helpful.

Everything electronic, gauges, radios, lights, door locks, power windows all work.

Tried starting in Park and in Neutral, no difference.

Vehicle is road driven only, haven't run over anything.

Need some help with what direction to go next in diagnosing problem.

 

Sounds like you have done several good steps so far.

Disconnecting the Cam and Crank sensors to see if you could get OBD2 back online was a good idea. You might need to disconnect the Throttle Position Sensor, MAP, and Engine Coolant Temp sensor as well. Just to be thorough in figuring out if one of the sensors is taking out the OBD2 bus.

You can also take a test lamp or multimeter to the OBD2 diagnostic port to at least ensure that its 12v positive and ground are available. They should be constant, even with vehicle OFF. You will need to look up the OBD2 port pinout online to know which pins to test. I recommend using a meter over a test lamp in this case (because PCM is involved). If you use a test lamp - it should be a PCM safe lamp (meaning it allows very little current through). Because we are dealing with circuits that traverse through the PCM.

 

On the Datalink connector, the ground pins ohm test showed low low resistance, however when doing the voltage test on pin 16, it show in the 8 volt area, though the batter is new and shows 12.54 volts at the power distribution box. Would that indicate one of the sensors has a short? or is the pcm failing?

 

hmmm...crickets....

So this am I am going to test the power one at a time to each sensor to see if one is causing a short.
Cam Sensor
Crank Sensor
Engine Oil Sensor
MAP sensor
Throttle position sensor.

If that doesn't reveal a problem, then I will replace the Crank position sensor.

Any input on diagnosis would be appreciated.

 

Haven't encountered this myself, but from what I understand, not connecting is the classic hallmark sign of a bad computer. That said, I would rule out exactly as you are doing, eliminating the sensors one by one. You should check voltages at the sensors +5 and +12, eliminate and see if they come back up. Have also read that harnesses on the fuel rail can short.
You left out the coolant temp sensor. Also check map tps ckps and cam sensor.

 

That is an unusual finding. I don't think the PCM or sensors would be my first concern. I would expect to find no more than about 1 volt less than battery voltage there. I don't have my 96 diagrams here at work, but I want to confirm exactly where that 12v at the diag plug comes from (pretty sure it does not come from the PCM). I have my digital dash displaying the OBD2 port voltage at all times - and it is usually between 12.4 and 13.1 depending on the temperature outside (the battery temp sensor will lower the system voltage as temp goes up).

Do a quick voltage test of your fuses in the junction block right behind the obd2 port - see if any of those seem low compared to battery voltage. (anything less than 11v should be noted).

This post has my attention because on a 96, when internal (inside the cabin) voltages drop off considerably from the battery voltage it raises concerns about the ignition switch and ignition switch connector - which tend to get burnt out by the AC blower fan over time (too much amperage through that type of switch and connector and it gets VERY hot when fan is on full speed). I'm not certain where the OBD2 port gets its 12v feed from though, and without my diagrams I can't be certain.

 

New OEM Crank Position Sensor made no difference.

"You left out the coolant temp sensor. Also check map tps ckps and cam sensor." tested, all at 5.5 volts

"Do a quick voltage test of your fuses in the junction block right behind the obd2 port" all tested ok at battery voltage

About 8 years ago the fan switch connector started to smoke and melt. I soldered on new thermal blade connectors and did away with the connector housing. Also replaced the fan and the fan resistor as maintenance item a few years later. I will say this, I live in central Florida and when the Jeep is running the a/c is on max and running full speed and that is all year long. Never do I drive with anything but max cold. Been that way for over 20 years..lol

Datalink port pin 16 is now reporting at 12.46 volts

The CPS I just installed was a new OEM Mopar that I ordered over 2 years ago and kept in my "extras" toolbox. When I went to install it the length was shorter than the one removed and it would not reach the connector. Also the connector was shorter though physically attached the same. I cut the connector from both sensors, leaving the old connector with longer wire and spliced the old connector to the new sensor by soldiering the wires together then applying heat shrink tubing. Clean splices, could of that destroyed the new CPS?

Turning the key on, no fuel pump hum, cannot connect to OBD2 adapter. Everything else seems to work fine as far as electrics.

Thanks for the suggestions, they help... you know what they say two, three or more heads are better than one (except in the kitchen)

Sort of stumped at this point.

 

I'll try to be more direct in my suggestion:

You need to open your steering wheel trim and inspect the condition of the ignition switch connector. It is prone to melting down in 96s. The insulation around the connector wires can also get brittle and allow amperage to jump to the steering column (grounded clean metal within about 1/4" of the wires). This is particularly important to check on those 96s that have utilized the AC fan at high/max speeds for extended periods of time.

When I get back to my FSM this evening, I'll be double checking the wiring diagrams in relation to your post.

 

Went out and removed the trim, visibly inspected and prodded with a torx driver. Everything looks clean and unburnt/hot and no "dust" came out when prodded.

 

Also, about a month ago I had the distributor replaced due to a cam position sensor fault. Long story short, after 3 different sensors, none fit correctly and caused a tapping. I ordered a new distributor and had it installed. While swapping out the cam sensor, I realized the distributor is installed 180 degrees out. The mechanic just moved the spark plug wires 180 degrees. Didn't notice any drive-ability or any other problem. Just wanted to mention it in case I am assuming wrong that it didn't have an effect on the pcm.

 

Connector and wires look fine. Hopefully ignition switch is fine, normally if its resistance gets too high you would see darkening of the wires. So we'll consider everything there normal.

Even if the distributor was 180 out, and the plugs were reversed (which I have no idea what types of running problem that may create, if any) I can't see what that would have to do with the OBD2 bus being unavailable. I'm going to have to check on that in the diagrams tonight. In the one video I have ever seen that dealt with such a problem, it was a failure of the dash to be properly grounded to the chassis (was on a 2000 xj). Only took 2 highly skilled techs about 8 hours to figure it out. Not before checking just about every other possible thing first. If you want to see the video for yourself (I know its a stretch):

Near the end (30 minute mark) is where they finally start to figure it out):

 

After checking all the sensors and install the new cps, I checked the fuse block under the dash as you had mentioned for any drop in voltage, since I was down there, I stuck the probe in the datalink port pin 16 and got 12.46 volts with key on or off, however the Torque app states no response from ecu.

 

Curious to know how you are troubleshooting voltages at the data link port. Do you have a troubleshooting guide to tell you what voltages you expect to see there? Because I think many of them are raw data, being waveforms that your DMM won't read properly. Myself I have never heard of probing that for anything other than DC such as 12 and 5 vdc and even then I have not seen data in the FSM for doing so.

 

One of the OBD2 pins is just a 12v feed. When someone plugs in a bluetooth wireless OBD2 adapter, it is that pin that powers the adapter. That is the one he is referring to. That pin, and the pin that providers ground are really the only two worth checking with a meter.

 

That is a good reading for the positive side. Did you test the pin that provides ground (since you are there?).