1990 MJ starts but won't stay running

[Epplebee]

1990 MJ 4.0 with AX15

Original problem was it sputtered between 1500-2000 rpm. Tested and replaced bad MAP sensor and since i am trying to make this right for my son, i replaced the 02 sensor, coil, fuel pressure regulator and CPS. 

Now it will run for a few seconds then die like the key was turned off. 

Battery voltage is where it needs to be.

Any other ideas or thoughts would be greatly appreciated. 

I am in desperate mode at this point

[Epplebee]

Also, new alternator, fuel pump and fuel filter.

[Ωhm]

Did it ever run good with the new CPS?

[Epplebee]

No. It had the trouble before the new CPS. My wife wanted all new parts and sensors on it since my son will be 5 states away after he returns stateside. 

[Ωhm]

Can you keep it running with say starter fluid or gas?

[Epplebee]

I have to wait a while before it will start back up. So when i can get it started i will let you know.

[Ωhm]

Swap your relays around with one another. Checking for bad fuel pump relay.

[Epplebee]

I did do that and no change. Fuel pump runs and puts out great pressure. I am thinking it may be igition related. Just because the coil is new doesn't mean its any good. 

[eaglescout526]

I would test that CPS too just to make sure it’s putting out the proper AC voltage signal for the ECU. 

[Epplebee]

I will do that when my wife gets home so she can crank while i test. If the cps is bad would it even start though?

[eaglescout526]

It could be strong enough of a signal to tell the ECU that “we are good to fire” but the signal could easily die out afterwards. 

[oldmanche]

We had a similar issue with our Renix.  Turned out that the fuel pump was getting power to start, but after it started.  The power to the pump comes from one place while starting but another once it is started.  If you have power to the pump after it dies than this is not your issue.  I believe it was pin 30 on the fuel pump relay that was not getting power.  Not sure if that's what you have going on but it's easy to check.

[Epplebee]

CPS is a constant .7 AC volts when cranking so i guess i can rule that out?

[Epplebee]

I went through and unplughed every sensor and re connected them and it fires up and runs. No clue on which one it was but its running now. Still has a sputter between 1500-200 rpm though

[Epplebee]

It now runs but besides the sputtering between 1500-2000 rpm, it will just shut off after running for 15-20 minutes. Hooked an actual fuel pressure gauge and it maintains steady pressure. It really seems to be ignition related i just can't figure out what exactly

[jdog]

next time it shuts off check for spark, bet your coil is getting hot

[cruiser54]

[cruiser54]

Jump the two wires together eliminating the resistor and see what happens.

[Minuit]

12 hours ago, jdog said:

next time it shuts off check for spark, bet your coil is getting hot

I've had this happen too, but it would start back up immediately after shutting down. So a dead coil may not stay dead for long enough to test for spark.

[Ωhm]

With KEY IN ignition switch wiggle it. Any slop? Is there extra weight on your key chain?

[Dzimm]

If you bought a CPS from the parts store, return it and buy a Mopar one.  The parts store ones are absolute junk and I personally have run into a multitude of stupid problems because of them.  Including the starting and dying one you are describing.  

[cruiser54]

Fuel pump ballast resistor may be getting hot. Jump it.

[Epplebee]

On 3/20/2021 at 7:31 PM, cruiser54 said:

Fuel pump ballast resistor may be getting hot. Jump it.

Fuel pump ballast resistor has already been bypassed by the PO, along with all of your other tips

[cruiser54]

With it running, start wiggling wire harnesses. 

[Epplebee]

52 minutes ago, cruiser54 said:

With it running, start wiggling wire harnesses. 

I have it fired up and running, been over 29 minutes so it seems like a new coil and wire fixed that issue. It still has a bad stumble between 1500-2000 rpms which i can't figure out plus seems to be running rich.