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electrical gremlins after engine swap

philbert

NAXJA Forum User
Location
minnesota
Today I finished up an engine swap in my 2000 classic. Everything went smoothly except for when I tried to fire it up. It cranks just fine, but right away I got the "no bus", the gas and alternator gauges didn't work, and I got no fuel pump hum with the key in the on position.

The no bus warning went away, but the rest of the symptoms persist. I have checked fuel pump relay, got power at pin 30 with key off and power at 85 with key on so that's good and I swapped out the CPS sensor too. There is no fuel at the rail. I haven't yet checked for spark. I have swapped out the fuel pump and ASD relays also.

Any ideas on what I should be looking for? To me I obviously have some sort of electrical short somewhere but have no clue where to look. Any ideas?
 
Those are the typical symptoms of Crankshaft Position Sensor failure. You should test the CPS, and inspect the CPS wire plug and wire harness. Look for bent or pushed back wire plug pins, loose connections, and physical wire damage.

The CPS can easily be crushed during an engine or trans swap, and moving the wire harnesses all around can cause broken wires or failed wire splices.



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standard.jpg






CPS Testing


TESTING PROCEDURE 1991 –2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals 2 and 3 (See Image). Ohmmeter should be set to the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.
 
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I swapped out the CPS already thinking that had to be the situation as the symptoms certainly fit. The connector is not by the intake on my Jeep, it's down by the connector for the 02 sensor under the car.

Looks like today I should start peeling back the plastic sheathing around the harness and check for broken wires.
 
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