Hello Jeep Enthusiasts, I am a newbie to the platform but I assure you I am very familiar with the Jeep Cherokee, as I have spent countless hours studying it.
Some information about my Jeep:
- ​​​​​1992 Jeep Cherokee Laredo
- Rebuilt engine which is a 97 4.0L built to factory specs
- 222,226 miles on the Jeep.
- 305 miles on the rebuilt engine
- Entire engine bay overhaul was done
- Everything in the engine bay has been replaced with
Factory or performance parts around 10K invested
- Original engine broke an exhaust valve on cylender 6, it still ran but I opted for a 97 engine to rebuild because I wanted to have the crankshaft girder and found one for a good price.
-So far I have worked out all of the bugs on this except for one, which had had me hung up for countless hours.

Onto the issue.. Any of your suggestions will be taken very thankfully by me and I would love to hear them! So I had my original oem crank position sensor give symptoms of going out. Jeep started to sputter, jerk and idle very poor. I replaced it with a Napa sensor and it immediately cured this issue and all symptoms went away. This only got me so far, as the symptoms returned about 2 months later. Typical for aftermarket sensors.. Since then I have not found a single sensor to get this thing to run. I have tried a few sensors off Amazon, O'Reilly, Advanced auto, Autozone, and Napa again. All sensors seem to produce a crank signal as my timing light shows that there is spark. Spark has been verified to be strong, no weak spark. Sparks plugs are all brand new Bosch iridium plugs. Coil is an Accell coil. Distributor is an aftermarket one I purchased off of summit racing with a brass cap and rotor. Plugs are Ignite 8mm plugs. Distributor was pulled a few times to insure proper wear on the teeth and proper timing index. All checked out good. Distributor signal is recieving 9v on the voltage wire and 5v on the signal wire. Signal is produced and fluctuates on the signal wire when hand cranking the engine. Crank position sensor is producing very similar signals 9v on the voltage wire, 5v varying current on the signal wite when cranked by hand. grounds are clean and Jeep cables kit has been installed, as well as a brand new interstate battery that has good voltage. Jeep seems to want to start when you hold the pedal to the floor, I imagine due to flooding from previous startup attempts. The cranking will accelerate but not reach a proper startup! I have searched the internet up and down for information and for an OEM sensor. The OEM part for a 91-93 had been discontinued by Mopar. Scrap yards and Upull do not have any, neither does Ebay for even a used OEM part. I decided to try something that I don't know has been done before and I purchased a mopar sensor for a 96+ Cherokee. 115$ I thought would be well spent. Thus sensor has a different style pigtail, but looks very similar and bolts up the same. I rewired my round style plug to it, soldered it all in, and insured I was matching the wires up correctly in the order they should be. After installing this I couldn't even get the Jeep to produce spark, so I assumed the sensor must be incompatible. But just to be safe, I purchased the same exact sensor, and triple checked that I wired it correctly, hooked it up to a scope and insured it produced signal before installing. Still the same results.. 230$ wasted on that experiment.. I am now starting to suspect my ECU may be bad, that is the only thing I can come up with at this point. I promise that my fly wheel is the correct one, and that the windows line up perfectly with the old one. The Jeep ran amazing before this, so I don't think the fly wheel could even be a contributing factor. I have pulled the plug on my ECU cleaned the connections and reinstalled it to insure it has good connection. I have traced wires and checked them for shorts many times. I have studied schematics to the point I practically have them memorized. Anyway I am starting to lose sleep over it and it drives me crazy. I am sorry, I know it makes it a little harder to narrow down considering I have touched everything in that engine bay in the past months. However I feel like there still could be something I am missing or that I am not the only one out there that has had this issue before. Any knowledge recommendations or expertise would be so greatly appreciated! Thank you guys, hope this thread is helpful in what you need to understand to give feedback.

A view of the engine bay...

 

Your serpentine belt looks loose :]

 

I have worked with a manufacturer to reproduce a reliable CPS for our Jeeps. If you are confident it's the CPS let me know if you want to give one of mine a shot.

 

I would be more than happy to try your one of the sensors you have in the works. I am quite certain this is the issue, given that some sensors will allow the Jeep to start up. However as soon as it goes into closed loop, or a few seconds after running it will spudder then die back down. After this it won't fire back up again for a while. I have tried multiple distributors, fuel injectors, spark plugs as well just to insure that those aren't the issue. You can also offer me any suggestions if you believe I am missing anything here. Thanks again, my email is Brendane5511@gmail.com if you want to reach me there, give me a price or information on getting the product.

 

Lol yes it's a picture of me assembling it, I promise you all that has been hooked up. I swear I had a newer picture but I didn't feel like digging for it

 

Unplug the o2 sensor and start it up.

 

Fuel pressure? Measured with a gauge

 

Yes I have tested the 02 sensor circuit and tried unplugging it to see if that would aid the issue. It still will not start. 02 sensor is a brand new NTK sensor, which I heard are decent for Cherokees. Even when I had the Jeep running but idling rough on a bad CPS, unplugging the 02 sensor didn't seem to alter the performance in any way. Thanks for this suggestion

 

fuel pressure measured out at 58 psi, upon priming the system. Fuel injectors have not been tested however fuel smell exits the exhuast when attempting to start and you can smell it when pulling the spark plugs. Spraying starting fluid makes no difference either which should eliminate the possibility of a fuel issue. Thanks for this suggestion.

 

Does removing the fuel pressure regulator vac ref change the rail pressure?

 

Are you sure CPS and CKS are synced?

 

They need to be pretty close to this:

 

Just a thought with no idea how to resolve it but could it be some sort of cps vs flex plate issue?

 

This is the part where I wish I owned an oscilloscope.. It is very possible my CKS is not producing the proper pulses or wave lengths. Right now I have a Cardone distributor and I installed a different aftermarket one during my test that had the removable style sync sensor and that didn't seem to fix anything. However I do wonder if changing the swappable sync sensor out for a more reputable brand would make everything happy. I might purchase an oscilloscope before any further investigation, because you bring up a great point. Also quick question, does a 92 have an ASD relay? Been hearing people telling me to check that out as well

 

Thank you for all of these great recommendations, I have heard about doing this but have not attempted it yet because I just installed a brand new fuel pressure regulator. Do I want to pull that vaccum line and then attempt to fire it up?