I have read through many threads and am a little confused.

For the car in the subject line . which is the primary fan (pass side or driver side) and which is the secondary fan (pass side or driver side)

Now to the operation, I have read about the primary and secondary fan operation in multiple ways but I have concluded like this

1. Primary fan is turned on by the ecm based on the input from the CTS that goes on the intake right under the thermostat housing.
The fan switch on the pass side head is an backup to that which turns on the fan regardless once the temp reachs the fan switch spec.

2. The secondary fan is turned on first when the A/C is turned on and second by the ecm once it senses that the temp is rising and the primary fan is not helping (I am not sure how it actually does that and what the routine is in the ecm?)

Is this correct ? maybe one of the ecm gurus can chime in.

Also I have read on a few threads that the fans can operate in 2 speeds? Is that true ? what is the exact routine for this happen ? how to test this ?

All this is part of my troubleshooting , why my car is overheating as well as running rich at the same time with no codes. Any help is appriciated.

 

I'm no guru by far, but I know some stuff. Primary fan on driver side , secondary on pass. side . This item from the technical articles section describes the stock set up. Check it out to start with
https://www.thirdgen.org/electric_co..._spec_mod_dual

 

Regardless of which side is which ... secondary should be turned on with A/C - so on a cold start, you can turn on A/C and see which fan is turning - THAT should be secondary regardless of whta side it's on (who knows whta's been switched/moved in last 20 years).

Primary - controlled by ECM through CTS like you said
Secondary - controlled by the fan switch (or the A/C)

 

Here is why my car does not agree with your statement.

Turning on the A/C turns on the driver side fan - so that should have been secondary.
New CTS on driver side head - 1 wire - that should have been for gauges
New CTS sensor below Thermostat housing - 2 wire - that should have been for ecm
New thermostat - 195*.
New fan switch on the pass side head an FS6 (grounds at ~201*)
I grounded the wire to the connector to check operation, the relay by the battery near passenger headlight clicks and passenger side fan turns on - so that should have been primary (call this primary backup maybe ???).

So in my case
1. Primary - controlled by the fan switch (call this primary backup maybe ???).
2. Secondary - controlled by the A/C

But I am missing the below operation.
3. Primary - controlled by ECM through CTS

I have no codes or check engine light. so is there Any way to check whats going on in the ecm or test the # 3 operation ?

 

Over the hundreds (probably thousands) of posts about fans, I'm not sure why this information can never get straight. It's almost as bad as breaking the myth of the oil pressure switch running the fuel pump...

Disregarding which side of the car the fan runs, it's irrelevant, completely.

TPI, Dual Fan Operation (is simple):

ALL years ECM controlled fan,

1) The ECM controls the primary fan (who cares what side). The ECM turns this fan on at 220(ish)°F
2) The ECM controlled fan will turn on with A/C request.
3) The ECM controlled fan will shut off at a programmed speed (general consensus says 35mph/56kph)

87 and older

1) The secondary fan runs only with the fan switch in the passenger head at 238°F

88 and newer

1) The secondary fan will run with the fan switch or, the (working) A/C turned on.

It's a very simple, elementary system.

Everyone thinks it is broken though because it's designed to run hotter than old crappy carb'd engines from the 60's-70's and the gauges in these cars can go askew from true reading over the years.


To test to see if the ECM is still controlling a (the, for single operation) fan, simply jump the A-B terminal on the ALDL with the KOEO (key on engine off). The CEL will flash code the the (ECM controlled) fan will run.

If it (the fan) does not run, there is
1) A power problem (fuses)
2) A relay problem (dead)
3) A wiring problem (broken)
4) A fan problem (motor toast)
5) A fan controller circuit failure in the ECM (rare but, it does happen)

 

Yeah usually both fans come on automatically with A/c on.

btw are both fans coming on? is it overheating at idle or driving down the road? is the air dam installed as well as the air baffle?

 

This is part of the problem (and I don't mean you specifically 89TBI, sorry), misinformation.
On '87 and older dual fan cars, both fans of a dual fan system do not run. The primary (ECM controlled) fan, only, runs on these.

Still, temperature is 90% of the issue half of the time. Everyone thinks the fan(s) should come on at a low temperature, they don't.

220°F is the lowest temperature a fan will turn on (ECM programmed)

If you want colder fan turn on temps, you have to:
1) Burn a new PROM with a lower (ECM) fan temp (like Hypertech does).
2) Use a lower temp secondary fan switch so the secondary is now primary.
3) Use an aftermarket fan controller like camaronewbie does which, works very well for him.

 

Thanks!