These damn fans, tried everything!

[coldkilla]

alright, the cars a 93 formula. i have a 160 stat with a pcmforless chip with programming to turn the fans on early. the other week they just cut out and neither will come on at the lower temp or the stock temp. ive replaced the coolant temp sensor in the water pump (that one goes to the pcm, the one in the head goes to the gauge), ive replaced the relays, i have voltage at the relay ports. WTF? i have to turn them on with my home made switch. what am i missing? everything should be working. is it possible that a power spike or something ruined the fan programming on the chip? is that even possible? i need this solved without paying big bucks before the summer heat gets here. any suggestions would be great, thanks!

[BonzoHansen]

Have they worked since you added your homemade switch? Why did you need such a switch? I take it you just tapped one (both?) of the ecm leads to complete the ground(s).

So you have 2 constant hots at each relay. When the car gets hot, is there signal at the relays (ecm should complete ground side of circuit)? You want to rule out the relays, the fuse & fusible links and work backwards. If the relays are good & the sensor is new, I might guess the ECM is a problem. Chips don't partially fry.

Are one of these diagrams right for your car?

GM LT1 early: http://img.photobucket.com/albums/v359/SIBLY/Cars/th_fan_schematic_1995_TOP.jpg (http://img.photobucket.com/albums/v359/SIBLY/Cars/fan_schematic_1995_TOP.jpg)
GM LT1 later: http://img.photobucket.com/albums/v359/SIBLY/Cars/th_fan_schematic_1995_BOTTOM.jpg (http://img.photobucket.com/albums/v359/SIBLY/Cars/fan_schematic_1995_BOTTOM.jpg)

[JL8Jeff]

I think there is something wrong with the fan portion of the ECM in these cars. My old 93 had the fans stop working unless the AC or defrost was on. So I changed to an SLP chip and 160 t-stat and they worked fine. Go to www.camaroz28.com or www.ls1tech.com and you'll find quite a few people having problems with the fans turning on. Do your fans come on when the AC is on?

[johnjzjz]

check the ground if you have power jz

[coldkilla]

all my grounds are nice and tight and clean. i have the switch so i can turn my fans on so i dont over heat. the fans never engaged with my ac on cuz, well, my ac compressor is bad and i cant turn my ac on, thats something ill get to eventually! there is the constant 12 volts at the relay and i just connect them with my switch to turn the fans on. when the car is on, there is another 14 volts present, that is not present when the car is off. all my fuses are good as they were the first things i checked. im sure one of those diagrams applies, im gonna print them out and see if they help. i just wish i had a way to test to see if the ecm is actually sending the signal to engage the relays and start the fans. im sure there is a way but i do not know it and those crap haynes manuals are no good. does anyone have a shop manual for a 93 formula firebird? the ecm is the unknown in this equation as ive replaced or checked the other factors. piss, piss, pissin me off....

[BonzoHansen]

The constant hot is the fan power off the fuse link. The switched 12v is ignition power (as per diagrams). That is good. You should be able to jump the ground, trip the relay and start the fans manually.

If you run an ohm meter across the circuits from the ecm, they should be open (infinity reading). When the car gets hot and they trip, the ground circuit is completed, giving you very close to a 0 reading. If the never happens, your ecm might be caput. I'd get a scan tool on it and see what it thinks the temperature is. If it is right & no ground, bad ecm circuit.

But why was the fan switch put in, was it overheating? How exactly is that wired?

[coldkilla]

The constant hot is the fan power off the fuse link. The switched 12v is ignition power (as per diagrams). That is good. You should be able to jump the ground, trip the relay and start the fans manually.

i have the relay for the primary fan removed and i have wires in two of the ports leading to a switch on my center console so i can manually turn the one fan on at 160. i didnt want to wire both fans up cuz it makes the wires very hot. but one fan cant hold the temp down at 160 so it creeps back up to factory 220 and stays there. ive got one wire in the #30 port and one in the #87 port.
i put this switch in because one day it started to over heat and i noticed that the fans never came on. so i troubleshot from there and now im at the point where the ecm has to be tested but i really dont want to go to a dealership and pay for scan testing just yet. the car is obd1 so i doubt that the parts stores could scan it for free for me, i think they only have the troublecode scanners and im throwing no codes.
Bonzo, can you explain to me barney style how to test the ecm circuit, where its at etc? electrical is my weakest area of knowledge.

[BonzoHansen]

You removed one of the relays permanently? The 87 & 30 circuit is the fan power, no? That is not the way to do it. I'll bet that wire gets hot. That also removes the ECM from the loop. My suggestion is put it back together the right way and start again. Unless I misunderstand what you did.

This is how you should have wired your extra switch (click): http://img.photobucket.com/albums/v359/SIBLY/th_attachment.jpg (http://img.photobucket.com/albums/v359/SIBLY/attachment.jpg)
Simple completion of the low amp trigger circuit by completing the ground.

Basic relay diagram.
http://img.photobucket.com/albums/v359/SIBLY/Cars/relay20info.jpg

[JL8Jeff]

Yeah, you should be using the relays to power the fans. You use your switch to turn the relay off or on and it's very low load on your switch and wiring. All the power goes through the relay to the fans and it's the correct gauge for it. If you're using 18-20 gauge wire from the battery to your switch to the fan theny you're overloading that wire big time and it could cause a fire. You can get a relay at the parts store pretty cheap and then get some 14-16 gauge wire to run from the battery to the relay and to the fan. Then you wire your switch to the relay. I had to do that with fog lights on my 4Runner.

[BonzoHansen]

Thing is, GM put all the wiring he needs right there. No need for any power to a battery. A run of 18 gauge to a cheap switch to complete the ground side of the trigger (low amp) circuit.

[coldkilla]

no im not running any lines to the battery. all i did is unplug the relay and put two wires with a switch in two of the slots where the relay sits and presto theres my fan switch. but this is getting away from the matter. i dont want a switch, any switch for the fans. i want the fans to work properly, with my custom chip telling them to come on at 160, like they did for the last year or so until they just stopped coming on. all parts in the line are good, relays, sensors, fans themselves, that i know to check so i guess my last resort is to take it to a dealership and get it scanned to see if the ecm is trying to turn the fans on or not and if it knows the proper temp from the sensor.