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Hey guys, here’s the scoop! I recently replaced the engine; it started up fine and everything worked correctly (idled in garage for about 5 minutes to look everything over). Shut it down, had to remove the battery and PS/AC bracket to make some adjustments (harness bracket on wrong side causing pulley alignment issue). Car sat for a few days. Then before I went to test drive, the cooling fans were always on low as soon as the key turned to the on position (engine off).
I ran a test light and the ECU relays (2&4) were triggering the fans. I looked through wiring diagrams all day didn’t come up with much. I swapped relays to confirm it’s not a sticking issue. Both 2/4 are grounded, both must be unplugged to turn the fans off. So here’s where it get’s interesting:
Removed the battery and alternator to look at the temp sensor and the issue magically disappeared… So I put everything back together and went for a test drive. After a few hundred feet the fans kicked on and the car died (had been running for 2 minutes, definitely not at temp). After about 30 seconds the fans turned off. Car started back up, ran for about 30 seconds then died when the fans kicked on again. So whatever is causing the fans to turn on will also shut the motor down.
I was very diligent with the engine swap. Pictures, service manual, torque wrench, new parts and all. Not sure what could’ve been disturbed or even where to start at this point. Factory ECU, no fan recall harness. Thanks in advance!
We've been PM'ing on this one. Typically the fans will run if you key on the car with no ECU plugged in which is making me thing it's a ground or connection issue. ECU is going offline, shutting the car down, and the fans are kicking on.
As mentioned above, huge thanks to Dale Clark for helping point me in the right direction over private messages!
The process was as follows:
-Checked/cleaned all grounds that were disturbed
-Pinned the ECU harness to verify power coming in and grounds were solid
-Floated in PFC to rule out ECU
-Sensor test showed water temp sensor (WTRT) failed at 4.99 volts
-Removed parts to access sensor (green connector behind WP housing)
-Noticed the fail was intermittent when the wires were moved
-Removed sensor and found exposed wire causing a short behind the connector
This normally wouldn’t be a huge issue; but with how the harness bends around the vacuum tubes, the wires became close enough to intermittently arc.
Also worth noting, the short would trigger the fans and shut down the stock ECU temporarily. However on the PFC, it would just show 4.99 and the fans remained offline. Yes I know I need to install the PFC already, I’ve seen the light lol. The intent is to break it in with the stock ECU then get tuned after the engine repair is sorted.
Included is a pic of the wires, in addition to the ECU pinout that helped troubleshooting immensely. Although this thread was short lived, hopefully it can help someone else chase down similar gremlins. Thanks again!
One last piece of information; after repairing the wires, there was still an intermittent open circuit from loose pins inside the connector. Not sure which condition was prevailing, but they're both fixed now and the problem went away. 100 miles on the new engine so far and everything is working correctly!
12-30-19, 02:38 PM
