Danno,
I am specifically asking you because you also have an 89 IROC-Z and you seem to know about fans.

The problem is that if I let the car idle for a long time, the fans don't kick in until about 230-240*F and then they BOTH come on. If I turn on the A/C when the gauge reads about 220*F, the fans still don't come on until about 230-240*F and again, both come on. This is with the stock EPROM. I have a Hypertech EPROM that I have used in the past and may try it to see what happens. Also, when I jump the ALDL connector as when checking codes, the fan comes on as normal and I get a ready code ("12").
Thanks for any help.
Jay

 

i'd like to know the answer also?

 

ALDL in service mode tell you ECM driver, fan relay and fan OK. What you need to know is whether the primary fan is getting a signal from the ECM at the proper temp to energize the pri relay. Temp for pri is approx 222-228 deg coolant temp. Aux with stock sw is 234. The only thing that could affect the pri operation is the CTS being out of tolerance. If both fans come on at the same time that suggests that the ECM is not getting info from the CTS, rather it is running in default mode. If the aux fan comes on without the pri fan running the ECM will by default turn on the pri. If thats the case then the only thing that tells the ECM coolant temp for pri operation is the CTS. I suggest you try to get someone with a scan tool and monitor actual coolant temp. In the AC there is a fan control sw, it feeds D-11 on the ECM connector. It is in the normally closed position. Meaning normally it grounds D-11 of the ECM. Some guys who take out the AC wind up with a continuous fan running until they ground that pin. Does the compressor clutch engage? Remember, the pri fan DOES NOT run immediately when AC is turned on, it only comes on when pressure gets to a certain point so there you could be chasing your tail. A low AC refrigerant charge could be the issue with the AC, if the fan does not cycle with the AC running for more than 3-5 min. I would attack the problem of the coolant temp first. Very important, when both fans come on do they turn on at "exactly"the same time? That's key to solving or narrowing down the problem. I worked on a bird that did something similiar, the pri did not come on when called for but then started to run close to the time when the aux kicked on. It was burnt contacts on the pri fan relay, the relay energized but the contacts were burnt and it did eventually run close to the temp of the aux. Try swapping the relays around. The fan relays caused more problems than anything else with the 89's. Get back to me when you can. Dan

 

Danno,
Thank you for the quick and detailed reply. When I got home yesterday, I replaced the stock EPROM with the Hypertech. I started the car and waited for the temp to go up. It took about ten to fifteen minutes to get just past the 220*F mark. I tried turning on the A/C at that point to see what would happen. The clutch cycled on and off (as if when needing a charge) and neither fan cam on. I waited a minute or so and turned the A/C off then after another minute or so the temp was in the 230ish range and the primary (driver side) fan came on. It seemed to be working properly. The A/C is probably not creating the needed pressure o activate the secondary fan. Using the stock chip, the fans came on at the exact same time.

Question: Could the stock chip be the problem? Does ist control the primary fan?

I recently changed injectors and while I was at it I replaced the intake manifold gasket, plugs/wires, rotor/cap, ign. module, O2 sensor and CTS . I wanted to make sure the car was going into fuel control as I had failed emmissions IM240 with high HC. The t-stat is a 180* I have been running for years.
Again, thank you for all your help!