No spark no ECU signal

[Junglekat90]

I have a 1990 wrangler with an OBD 2 4.6L stroker. A few months ago i went off roading and about half way through the day the jeep died and wouldnt start (no fuel, no ecu, no spark). while being towed out of the trails, I heard the fuel pump turn on so i turned the key and it started. I drove for about 15 minutes then it died again. THen while being towed it i heard the pump kick on and it started and ran the rest of the day. From then on driving on the roads was fine until last weekend i stopped to wait for cars to pass to make a left and it died in the middle of the road again with no spark fuel or computer. In attempts to figure out whats going on i still had warranty on the computer so i got another one. put that it still has no spark or computer signal but I am getting fuel except it doesnt shut off. so you turn the key the pump comes on and when the system is charged it used to shut off now it stays running. I am about to try another CPS to see if that is the issue. Any other leads on where to look?

[gradon]

Bad fuel pump ground.

[BADASYJ]

By chance were you wheeling in deep muddy water? If so my first move would be to get another CPS.
Check all grounds, OBDII is very unforgiving when it comes to electrical issues. Everything electrical runs through the CPU one bad ground will shut you down...

[Junglekat90]

did try a new cps no difference ill check the ground on the fuel pump

[jsawduste]

The ECM has 2 grounds and 2 powers.

You can go to the Morris 4x4 website knowledge center and download the factory service manual.

Once you have the download you can go to the 3 ECM connectors and trace the power and grounds.

One of the grounds is for each sensor requiring such. The other ground is for the ECM itself.

The fuel pump and the ASD relays ground to the ECM for example. As do each of the injectors.

One power supplies a constant 12v while the other 12v supply is energized in ignition Ii and III.

Honestly is a simple setup and if you spend a few minutes with a wiring diagram you should become well versed.

[jsawduste]

What don't understand is you say a 90 YJ which is RENIX then say an OBD2 stroker.

What engine control system do you have as the two mentioned are vastly different.

[Junglekat90]

The jeep originally had a 4.2L i swapped out that motor for a 4.0 out of a 97 Cherokee running an OBD2 setup.

[BADASYJ]

The dreaded OBDII electrical gremlin has come back to haunt you again. I see you are on your third ECU now. What was the cause of the no idle issue you had last time?

[Junglekat90]

Well i found the problem. after some searching on what causes failure in communicating with the computer it can be a short in any of the 3 wire sensors. Turns out since im using the 2 wire speed sensor the third wire for the original sensor got lose and was shorting out on the transfer case skid plate.

[jsawduste]

That would kill the sensor ground circuit.