Hey Team

I was driving my 1989 cherokee home the other day and it suddenly died, I was able to coast to the shoulder then got it towed home.

Attempts to start it would crank but no start.

what I have tried

1) starting fluid - no change
2) replaced ground wire from battery terminal to engine block (casing was melted /cracked) - no change
3) All relays in engine compartment checked, they were all good
3) replaced CPS sensor - no change
4) replaced ECU - no change
5) pulled one of the spark plugs out, confirmed there is spark
6) fuel pump does prime when key in on position, I poked the nipple on the fuel rail and got a spray of gas so I have fuel pressure.

one weird thing I noticed is when I pulled the CPS sensor out I checked the plug going back to the ECU with my multimeter and got around 3.4v from both prongs...im not well versed into automotive electronics but I believe if my googling is correct I should get 5v from one prong and 0 from the other ?

I dont have much automotive experience and am running out of ideas of things I can check myself before having it towed to a mechanic.

you guys have any idea on whats going on ?

Dramatic pictue of my jeep below.

 

Do you know if you have fuel pressure at the rail? I just went through a full crank, no start situation, and it ended up being the fuel pump assembly, most likely the regulator. The only difference between my symptoms and yours is that my jeep would almost start when I sprayed starter fluid.

 

A squirt of fuel from the test port is not sufficient to test fuel pressure. You need to put a fuel pressure gauge on it and see that pressure you get when it primes, then while you're cranking it. You can likely "rent for free" a fuel pressure tester from your local autoparts place. Bear in mind that you have a fuel filter located near the fuel tank. Often ignored, it can get clogged and reduce fuel flow.

Normally, if it runs on starter fluid, it's not a fuel problem. To be sure, remove the air tube from the TB and spray right down the throat.

Also try bypassing the ballast resistor on the inside fender wall (although I don't think this is the issue, but we can rule it out).

 

You can rent a fuel pressure gauge, pop it in the fuel rail and see what the pressure is at crank. I had a similar issue to you not too long ago.

Fuel rail pressure for me is 38psi at crank.

You mentioned you have spark but it might be worth checking the ignition coil and just making sure it meets all the resistance thresholds. My ignition coil didn't meet these thresholds so I replaced it but car still didn't start. Cleaning the pins on the ICM fixed my issue.

I would also take the time to spray electric cleaner on every connector you see just in case. Have you also cleaned or checked out the C101 connector?

 

I don't think you should be seeing any voltage on either terminal of the vehicle side of the CPS connector. The white conductor is the ground from the ECM and the violet wire is the input to the ECM. Voltage is generated by the CPS itself. I attached a wiring schematic. Sorry it is marked up for grounds, but you will find the CPS input and ground to the ECM at the top at C1 and D1. Check out Cruiser54's tip on testing the CPS: Renix CPS Testing and Adjusting | cruiser54