90 SC COOLING ISSUE Please Help

barberben

Registered User
Ok guys, I've spent the last hour searching and reading up on common cooling fan issues, and can't seem to find a fix for what I have going on. Most of what I've read is from guys dealing with 94's and 95's. Don't know why that is, but their setups must be different from my 90 SC.
My fan doesn't come on due to the temperature rising. It DOES come on when I turn on the A/C and it also DOES come on when I unplug the ECT resulting in the expected CEL or check engine light. I want to try the KOEO test but though I've searched my @$$ off I can't seem to find out how to do that. I'm sure one of you guys has the answer I'm looking for so I'll say thanks in advance.

barberben
 
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Sounds like your IRCM is bad ( Common problem for 89-93 ). It is the little white electrical box behind your passanger headlight and under the air box silencer. It has like 30 wires plugged into it. To test to see if your low speed fan is bad or the IRCM is to find the #11 wire( they are all numbered ) coming out of the IRCM and cut it. Leave enough on each side to resplice it incase its your fan and not the IRCM. If the low speed fan comes on than you know its the IRCM, if it doesn't come on then its your fan motor or tempeture switch.
 
Thank you so much for your reply. Are the IRCMs replaceable on these early model SC's? From what I've read the 94's up weren't. Also what about the temperature control switch can it be tested? Lastly, do you know how to perform the KOEO test?

Thanx
 
To test the temp sensor, just pull the connector off it. Failure mode is to turn on the fan so the fan should come on. The temp sensor is mounted on the passenger side of the blower toward the front of the intake manifold on a tube that comes out of the intake manifold and a heater hose is connected to.

There is a sensor on the thermostat housing, but that is the one used for the Gauges.
 
Yeah. I did that, and it comes on, so it must be the IRCM. Where can I get a replacement?

Looks like both A1-Cardone and Standard Motor Products will take yours and rebuild it for you, at the cost of about $120 through www.rockauto.com.

You can post in the wanted to buy forum and see if anyone has a good one they can sell you.

But if you said you disconnect the EEC-IV temp sender, and the Fan comes on, that tells me that the IRCM is working just fine, and that the problem is more likely a bad temp sender for the EEC-IV. Unplugging the sensor causes the EEC-IV to get a out of range value for engine temp. Since it can't see temp anymore it fails safe and tells the IRCM to turn on the low speed cooling fan.

If the fan comes on, that means the IRCM is able to control the fan based on input from the EEC-IV. That means the IRCM is working properly.
 
Actually, pulling the plug on the ECT sensor like that will cause the EEC IV to go into fail safe mode so to speak, and that turns on the high speed fan, not the low speed. Turning the A/C on will crank up the low speed fan, which sounds like that is working as well, which means the IRCM seems to be working fine.

As Mike mentioned, if the ECT sensor is not reading right, that could be the cause of the fan not coming on at the right time. I will caution you though, if you are going by the factory temp gauge, then don't. That thing is so tempremental it should be shot on sight. So many folks have fallen for that trap only to find out the car was running fine all along. The stock "tune" requires the motor to hit 220F before it turns on the low speed fan, so it will appear to go frighteningly high on that stupid gauge, especially when its in one of its moods that day.

Verify the temperature with a heat gun on the tstat housing, or better yet, get a real temp gauge.

Fraser
 
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