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Fuel and Cooling Issues with P0172, P0650, P1258 on 1984 Jeep CJ7 with 5.3L Vortec Engine Swap

Model: 5.3L Vortec Fault Code: P0172 Posted: 2017-09-05 11:23

Hi everyone! I'm looking for help diagnosing some serious issues with my 1984 Jeep CJ7 that has a 2000 5.3L Vortec engine installed, along with a 9-inch Ford rear axle. The vehicle initially performed well after the swap — lots of power and no problems. However, during my drive from Vegas, it started exhibiting intermittent symptoms: sudden power loss, stalling, backfiring, and then briefly returning to normal for about one minute before recurring. This behavior has become more frequent and now persists even at idle — the engine barely runs and struggles to maintain a steady idle. The check engine light (MIL) is on consistently. I've pulled these diagnostic trouble codes: P0172 (Fuel Trim System Rich Bank 1), P0650 (Malfunction Indicator Lamp - MIL Control Circuit), and P1258 (Engine Coolant Overtemperature - Protection Mode Active). What could be causing this? What should I check first to resolve these issues? Any experience with similar setups or known common problems when swapping a 5.3L Vortec into an older Jeep CJ7? Thanks in advance for any insights!

Related fault codes
P0172P0650P1258
Comments (4)
Anonymous 2017-09-05 11:35

Kev2 Thanks for the detailed response — I'm considering taking it to a specialized performance shop. Would a shop with experience in engine swaps and OBD2 diagnostics be better equipped than trying to fix this myself?

Anonymous 2017-09-11 11:24

Is the MIL/CEL light actually visible on the dashboard? It's important for diagnosing P0650 and other related issues.

Anonymous 2017-09-11 11:25

Yes — the check engine or 'Service Engine Soon' light is present. The PCM detects an issue with this light, which may be linked to a faulty sensor, wiring, or ECU communication problem.

Anonymous 2017-09-11 14:40

yes - the check engine or service engine soon light. The PCM see a issu e with the light.