Need direction had to have the Jeep towed home yesterday lost power all of a sudden. Checked the codes 12 and 5555 / 5555. I checked the fuel pump (jumpered 30 and 87 to relay) I hear the pump working. Is is safe to assume that the crank sensor is good? I did not check for spark yet. Any other items I should check? Thanks.

 

It's never safe to assume anything is good without verifying that it is good. The best places to start are to check battery connections, engine ground points and a spark. Checking connections and ground points means removing and cleaning up, not a visual inspection. There'll be more things worth checking which I'm sure others will suggest.

 

Not sure how you went from jumpering the fuel pump relay to assuming the crank sensor is good. When you say lost power, did it stumble and die like it ran out of fuel, or just drop dead like you turned off the key? Checking for spark would be the next easy thing to check. No spark could mean a dead crank sensor and will often not set a code.

 

I'm voting for failed crank sensor.

 

To clarify I jumped the fuel pump relay #30 and #87 and heard the fuel pump running. Today, checked the Crankshaft Position Sensor on the transmission tests fine. Tomorrow will check the coil to determine if spark is resident. What should the resistance be across the primaries (low / high) also what should be measurement for the primary/secondary measuring to the post going to distributer. Will check that I have constant 12V to the coil. Ran the codes still have 12 and 5555. Should I not get additional codes in a no start situation?

 

Check the tires for air. doesn't 12 mean the pcm lost power?

 

12 means battery disconnected within the last 50 key cycles and 55 means end of codes. I'm not sure why you'd get 55 twice. As I'm sure you know, these vehicles are nowhere near as smart as a modern car so unless it can detect one of a rather limited list of things, you won't get a code for a lot of things. More especially being a pre 96 relying on flash codes.

 

Just tested the coil no spark. Removed unit bench tested using meter 1.1 ohms to each pin. Tested each pin to the spark plug male end; both primary and secondary measure 9.84 ohms. That seems somewhat low seems to me those should be higher for the primary and secondary?

 

9.8 kilo-ohms sounds more reasonable for the secondary (spark plug to ground), and 1-2.5 ohms for the primary side. Are the injectors firing? Use a noid light or a meter backprobing an injector and watching for the voltage to jump around (or set the meter for a/c). I'm leaning guessing a bad crank sensor myself. When they go bad, you get no spark, no injector action, and nothing on the tach as the computer just doesn't think the crank is turning. They usually either fail completely, get intermittent or become temperature sensitive and crop out once they get hot.

 

Replaced the CPS today with a new Napa Echlin sensor. Also, replaced the spark plug wires as a maintenance issue last time replaced 2017. Still no spark? Will check to see if I have a constant power to coil pack and a signal wire. Will report back.

 

Oops. My bad see below.

 

Took a look at the wiring today going to the coil and saw the following (see attached below image). Also, measured the primary, and viewed a video on-line stating the min / max for the measurement should be 0.97 ohms to 1.18 ohms. Mine measured 1.1 ohms within range. Also, the secondary measured 6.87 ohms for both low and high readings. Again, according to the video the low / high should be 11.3 ohms and 15.3 ohms respectfully. My original coil from the factory seems to be measuring too low and on the way out. Will replace the connector and coil and report back tomorrow. Thanks for the guidance.

 

The values below are per the 1994 Cherokee service manual. I'm not sure what you mean measuring both secondary pins? You should be measuring between the coil output wire and ground. Good resistance doesn't guarantee that it's not arcing over inside.

Coil Manufacture: Diamond
Primary 0.97 to 1.18 ohms
Secondary 11,300 to 15,300 ohms

Coil Manufacture: Toyodenso
Primary 0.95 to 1.18 ohms
Secondary 11,300 to 13,300 ohms

You can hold the coil output wire ~ 1/2" away from a solid ground (using insulated pliers) and you should have spark when you crank.

Connect the coil, and backprobe across the connector with the meter set to voltage. Then per the FSM:
" •Crank the engine for 5 seconds while monitor-ing the voltage at the coil positive terminal:
• If the voltage remains near zero during the entire period of cranking, refer to On-Board Diagnostics in Group 14, Fuel Systems. Check the powertrain con-trol module (PCM) and auto shut down relay.
• If voltage is at near battery voltage and drops to zero after 1-2 seconds of cranking, check the cam-shaft position sensor-to-PCM circuit."

 

Replaced the coil and connector today, Jeep fired up. Appears that the issue is a combination of the the connector and coil being bad. Curious why the ODB1 code for coil pack never came up? Thanks to all that provided assistance. Thank you.