Bah! I replaced the coolant sensor for the computer thinkin it would tell it that its getting hot enough. I know the fan has the ability run, because when I jump the computer to show error codes, the fan turns on. But normal driving, the secondary will kick in when it gets really hot, all the while the main fan never budges. It doesn't matter if the a/c is on or not. When I put my new Jet chip in, it didn't make a difference. So I don't think the PROM is to be the cause. So what could be the deal?

 

I'm not familiar with Jet chips, but it could be the fan on temp is set way high. Does the fan work with the stock chip?

 

No. Didn't work with the stock one either. I thought maybe the new chip would help, but nope. No such luck.

 

Did it work at one time, and now it doesn't? Which sensor did you replace the one in the manifold or the one in the head?

 

Naw, it never worked. And I replaced the sensor in the intake manifold, the one used for the computer, not the gauge.

 

Just for giggles, if you havent tried it already, unplug the connector on the fan switch in the passenger side head and, with the key on, ground it to the body. If the non-working fan turns on then you need a new switch.

 

Done that. The switch is good for the secondary fan. That ones ok. And I actually have an aftermarket switch installed to make it come on at a lower temp. And if I ground out the computer fan, it turns on. But for some reason, it's like the computer just isn't telling it to turn on.

 

Is it possible that the low temp switch is keeping the coolant from reaching a high enough temp to kick on the primary fan? I have no experience with aftermarket fan switches, maybe somebody whose used them can chime in.

 

Yes, but here's the thing. I have a 180 degree stat, and at 180 the secondary fan with the aftermarket switch comes on. Keeps it somewhat cool. But, in the hot summer, when the car is sitting in traffic the needle can go past 220. Usually the computer would kick the main fan on, bringing the temp back down. But, nothing happens.

 

If you have AC, turn it on. The primary fan should come on regardless of temperature until you exceed 30 mph. If it doesn't come on, then you have a problem with the circuit.

With the stock eprom, the main fan doesn't kick on until almost 210*

 

Ah. Now we be gettin somewhere. The fan doesn't turn on with the a/c, but the a/c system does work. So...Any suggestions?

 

I have been looking over all of my wires and still can't find a physical break in the circuit. I'm lost. Any ideas?

 

One of the ac lines off the compressor, the one on the frame rail, there is a pressure switch with 2 grey wires on it, this switch is responsible to turn on the fan, among other things, with the ac. If the switch or wiring are bad it may cause problems

 

Umm.. Could you explain a little further, I'm confused. Thanks.

 

On the passenger side there are 2 lines coming out of the condensor. One goes to the compressor, the other goes along the frame rail toward the firewall, there is a pressure switch on this line. If that switch or the wiring is faulty it could be the cause of your problem

See the attached wire diagram

Edit, looking at the diagram, the ac switch is only connected to the secondary fan, sorry
hopefully the diagram will be of some help

 

Yeah. It looks like only the ECM has control over it. I know it should have control, cause if I jump the diagnostic port terminals to show the error codes, it fires up the fan. The signal is getting to the relay to turn it on, but how come not under normal conditions? I'm thinking maybe something with the ECM itself?

 

According to the diagram, the primary fan relay has only one ground controlled only by the ecm, when you ground the diag connector and the fan comes on, that means that the ecm and all assoc wiring are good. Your back to a bad coolant temp switch (doesn't matter if it is new or not), or your system does not allow the temp to get high enough to kick on the fan.

The gage is not an accurate way to read your temp. In my car I set the fan on temp at 215, yet the gage reads almost 250 before the fan comes on.

I'd be willing to bet that it would work if you put in a 195 tstat and stock fan switch.

 

But, it never worked when it had the higher stat. It got hot enough to turn on the secondary fan.

 

Bump

 

I was thinking, maybe the computer is junk?

 

I'll throw in my 2 cents.. I have the same problem (92 Camaro 3.1L).. I have only one fan though.. It comes on if I ground the relay coil (what the ECM does to turn it on). It comes on if I plug in the Test Plug... It does not come on if I turn on the AC and it does not come on if the heat gauge goes off the scale.. Anybody know if the switch in the intake (two wires to it) is a true switch or it has variable resistance.. If it is a switch does it just jump the two wires together or does in ground them to the block?? If the fan comes on with the Test Plug, then the ECM has a good output circuit to the relay.. But, the ECM may not be reading the input from the fan switch on the intake or the fan pressure switch on the condensor and telling the output to turn on the radiator fan.. Anybody have a connector pinout identification drawing for the ECM box..??

 

It's not the right way to fix it, but you could use the signal wire from the secondary relay to ground both relays. This is what i've done and I'm happy with it, except I use my primary signal wire to ground both relays.

 

if you have access to one try swapping in a different ecm, one that you know is good, and see if the problem goes away.

 

Well, My fan does kick on after all... My alternator was out so the electrical was too low to get the fan to run... Now I have a different, fan kicks on engine dies or runs rough... Will start a new thread on that though...

 

So, LarryD, did the alternator swap did the trick? Cause it seems like you have the exact same dilema! And thank you all for your help!

 

Well, maybe only to add to the confusion... Somebody in the past had an old alarm system installed. The wiring is quite the chopped up mess in the engine bay, but everything else works. To my knowledge... Something could have gotten cut?