Hello everyone. I have a problem with my jeep engine swap. I had the 4.2/258 engine and BA 10/5 transmission. I installed a 4.0 from a 1998 jeep grand cherokee/zj, it was starting and running really good. I also took the chance to change for a ax15 transmission and put the np242 from the zj. I took the zj engine wiring harness and remove stuf I didn't need like transmission and A/C controle. I did a stand alone wiring harness. The only thing left in the back part of the wiring is the speed sensor. Now the engine starts for 2 to 8 second then dies. This issue is constant and repeatable.
Current Setup & Mods:
Tests & Observations:
Diagnosis So Far:
If you have question about anything for this feel free to ask them
Current Setup & Mods:
- 1998 Jeep 4.0L engine
- Standalone harness from 1998 Jeep ZJ
- New programmed PCM (confirmed for 1998 4.0 ZJ)
- Aftermarket fuse block — every PCM circuit properly fused
- ASD relay properly wired (Bosch-style, confirmed working)
- Fuel pump and pressure confirmed good — pump is on separate circuit and runs continuously
- Injectors, O2 sensors, and ignition coil powered separately
- Crank position sensor replaced with new unit
- Park/neutral switch circuit grounded
- Camshaft position sensor connected
- Spark continues after engine dies
- Confirmed the PCM cuts fuel injector pulse when it shuts down
- All the ground are good, tight and clean.
Tests & Observations:
- ASD relay powers up properly on key-on and while cranking
- Spark continues even after the engine dies
- Injector pulse is present during crank/start, then is cut before engine dies
- Unplugging the cam sensor = no start at all (confirms cam sensor is required)
- Tried multiple relays and confirmed all PCM ignition feeds have proper 12V during crank and run
Diagnosis So Far:
- Crank signal is good (new sensor, confirmed pulse)
- ASD relay logic works properly (no wiring or fuse issues)
- PCM sees crank and cam signals long enough to start the engine
- Since spark continues, but injectors cut, it's not ASD or crank signal failure
If you have question about anything for this feel free to ask them
