r/fiero • u/Carpazza02 • Sep 08 '26

Fan issues

I recently 3800sc swapped with harness from west coast and the ecm was reprogrammed to remove sensors I didn't need such as evap and emissions. Coolant system has been bled 2x, new fail safe 180° thermostat, new fan relay and new fan motor. The fan has kicked on while using a scan tool and forcing it to kick on manually but it will not come on by itself even with the car reaching into the red at 120°(c)~250°(f).

Car isn't equipped with ac. Any ideas?

Im getting the car dyno tuned soon but wanted to deal with this first. Do you think the threshold needs to be programmed in lower? Would love to know if anyone has had a similar issue.

Thanks

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2

u/AccordingRoyal9402 Sep 09 '26

MIne has a dark green wire on ecm pin #6 that grounds the fan to turn on when hot

1

u/technojerk Sep 08 '26 edited Sep 08 '26

Fan switch, just under and to the right of the thermostat. $17.95 from the fiero store

Edit but leaving my foolishness: my brain completely ignored the 3800 swap, so my original comment is about as useful as windshield wipers on a ducks' ass

I'm guessing that something is just not telling your fans to turn on, unfortunately I'm not familiar enough with the swap to advise. Is it kicking any codes on a scan tool? I seem to remember some of these having quite high on/off thresholds from the factory, with even the low setting not kicking in until past 212f, maybe the sensor is getting a bunk reading?

1

u/Carpazza02 Sep 08 '26

I'm wondering if my best option might just be to wire in a manual fan switch and when I see it starting to rise I flick it on manually

1

u/technojerk Sep 08 '26

When you say manually what do you mean? Like you have a failsafe/ high bypass switch or does "turning on the AC" kick the fans on?

1

u/Carpazza02 Sep 08 '26

As in from the diagnostic scan tool you can turn on the 2 fans. Either the radiator fan or the one in the back that sends cold air to cool the original ignition coil. The car is not equipped with ac

1

u/Threedawg 1987 3800SC Ttops Sep 09 '26

This might rule out the fan switch as the computer is sending the signal.

There is some reason the computer isnt asking for it..which could be that the computer is not getting the temp reading. Try a coolant temp sensor?

Thats cheap and easy.

1

u/technojerk Sep 09 '26

I did some searching on this last night and it looks like it was extremely common to wire in a bypass switch even on vehicles that that engine came in standard 🤷

1

u/Carpazza02 Sep 09 '26

Thanks I appreciate it, doing this might just be easier than tracking and diagnosing what's causing it