1992 L98 formula with dual fans. Passenger side fan turns on as soon as the key is turned to 'ign'. Driver side fan is off. I know this does not sound normal and am wondering where the problem may be. I tried looking at the wiring and it did not look like it was monkied with. Car is stock but has a hypertech chip in it. Thanks for the advice.

mines doing the same. ever figure it out?

sounds like the cooling fan relay is stuck. just replace it.

is your defroster or AC on?

it does it with them off or on. doesnt make a difference.

isn't this a sign of the car being in limp home mode?

I've been working on the same problem. For me it's not the relay. I can unhook it and hook it back up and I can hear it switching. It makes a clicking noise. If it's stuck you won't hear that.

Could be the thermastatic switch on the pass cylynder head.Sometimes when they fail they stay in the on position.

Good catch! I overlooked that on the wiring diagram. That's my next check. I'm pretty certain that's it.

I agree with 84; the switch in the head, when working, grounds out the circuit and the fan turns on. If its frozen in the on position, the fan will constantly run when the ignition is on.

I had done something similar on purpose on my last vehicle as a quick fix; removed the connector from the wire, crimped an eyelet on it, and grounded it to the body. You go through fan motors a bit quicker, but the fan is always cooling.

Is there a fuse in your box labeled fp fan fuse? If so, with the ignition switch in Run, remove the fuse. If the fan continues to run, you probably need to replace the heavy duty coolant fan relay. Before you replace it just swap it with the other cooling fan relay and see what happens.

after a little more work this is what i have. 89 iroc dual fans 305 tpi. when you turn key on passenger side fan comes on. as soon as you start it both run. i unhooked the sensor in the passenger head. after that when you turn key on passenger side fan wouldnt come on. when you started engine drivers side fan would come on for about 10 seconds then go off. i put a new sensor in the pass. head tonight. now im right back where i started. right fan coming on with key and both on when engine is running. any ideas? i'm almost done with the car. this is one of the few things i have left to figure out. any help would be appreciated.

Did you try what I suggested to the OP in my last post?

What I suggested was free.

no i havnt tried that. i will give it a try tomorow. thanks for the response.

Could be a bad chip

ok i did have the fuse lableled as you said. i pulled it with the ignition on. when i did that the fans stoped. i then started the motor and neither came on. with the car running i re installed the fuse and both fans came on. any other suggestions? thanks guys

Have you tried unplugging this (attached pic) ?

i have the same problem isnt the fan computer controlled

Ok, the info I'm giving you is speaking for the passenger side fan. This info is coming from my 88 service manual. It says if the fan stops (which you said it did) then check the DK Grn/Wht wire, gray and black wires coming from the heavy duty coolant fan relay and, the heavy duty coolant fan switch for shorts to ground. The heavy duty coolant fan relay should be on the passenger fender. The heavy duty coolant fan switch is above the starter. You'll probably need to get that from underneath the car.

Is that the coolant fan switch on his engine?

I have the 350

Fan switch is in the same location for all v8 motors.

That is the fan pressure A/C switch. It is directly linked to the secondary fan to make it run (via ground) and also is one of 2 inputs to the ECM for A/C request.
If the switch were stuck closed, the secondary fan would run always (ignition hot) and the ECM, after start would run the fan due to the fan input request.

It's really just a guess though.
It's the only common link to make both fans run though, aside from a ground fault in the secondary fan circuit to give a false fan request signal to the ECM. .

ok i just went out and unplugged the a/c pressure swsitch and it made no difference. where do i go from here?

the heavy duty fan switch above the starter. i think thats the part i just put in. its round and between the 3rd and 4th spark plug. i think we are talking the same part. the only othing i see above the starter is a loom with some fusable links. and one black wire that runs to the switch i just changed. also the wires for the starter come out of it as well. i left the key on with the fan running and i unhooked the wire into the new sitch i just put in. they stopped running. i know this grounds so it would stop. dont know if this info is usefull in diagnosis, just thought i would share everything i know.

Yes, that's the part. Kind of a pain to get to and coolant comes out when you pull it out?

yup. had coolant on the floor. yeah i replaced it last week. when i got the coolant back in and all buttoned up i let it run for about 20 minutes. the top radiaitor house got hot likle the thermostat opened. do you think theres a possibilty of an air bubble in there. like i said i let it run a while. but it will only get so warm with both fans running.

Have you inspected the wiring for shorts to ground ?

i've glanced it over. tomorow i'll have to sit down and really look it over.

Buy process of elimination, I think the issue is narrowed down to a fairly fine point.

The only really confusing part of this is, the switch, at the point of the harness plugging to it, should be isolated from the block (ground).

A bad plug or switch would be my next two guesses.

hey guys
wanted to thank you all for the help. i fixed it tonight. i bought another new fan control switch(in passenger head). i swapped it out, and it all works like it should.funny thing is i was talked into buying the more expensive one, you know so i wouldnt have any problems. lol. so once again thanks.
doug

Glad you got it

you and me both. im hoping that i can put plates on her finally maybe monday or tuesday. then i can see if the last 4 months was worth it.

hey guys im back again. wow this thread is old. as i had stated previously the switch i installed took care of the passenger side fan. well now i have a different problem. the drivers side fan, it is coming on when the temp gauge reaches about 130. so it comes on and stays on. what controls this fan? is it another switch like is in the passenger side head? the passenger side fan seams perfect. when it gets hot it comes on. its just the drivers side thats driving me nuts. ive been working on this convertible for about 2 years and have put about 200 miles on it, i just want the thing right and dependable. thanks guys any help is appreciated.

The ECM. It gets it temperature reading from the CTS (coolant temp. sensor) in the front of the intake under the throttle body, TPI.