Primary fan won’t kick on unless I jump it at computer plug in. The secondary fan does kick on at about 240. I tried a new relay for all three relays along the firewall. It’s a 1990 with a 305. Allegedly before I purchased the car all three temperature sensors were replaced in April. Obviously both motors are working. The other strange thing is I can’t turn on the secondary fan with the air conditioner or blower. The only time that motor kicks on again is when it’s over 240. Any thoughts?

 

Check to make sure you are pulling the right relay. The one that went bad on my 89 was up by the battery. Replaced it and primary fans kicked on again.

 

I tried all three, at 230 on the temperature gauge. Shutting the car off in between changing each relay

 

But the battery is not by the firewall... there should be another fan relay right behind the radiator next to the battery assuming you have a dual fan setup. I chased the same thing - I replaced all the firewall relays and nothing was fixed. It wasn't until I replaced the relay by the battery that my primary fan started working. If the relay is bad and the ECM is calling for fan it should kick right on right when it is replaced.

 

Actually I think it is the one on the passenger fender behind the battery that is part of the fan harness. Check these guys

 

My engine is a 305. I don’t have any other relays near the battery or radiator.

 

It might be tucked up inside the fender. Mine was held up by a plastic push pin. I'm not sure what the correct location or attachment method is. It has to be in that area though just due to how the fan harness is laid out. I looked up the fan harness and it is the same for 350 and 305.

https://www.ebay.com/itm/311784526637

 

Yes sir I looked around, I can look a little better later but I have three alongside the firewall that are direct plug-ins for the wiring harness you just sent me

The wiring harness is that around the radiator do not have any relays attached again from a quick lock

 

The three along the firewall are fuel pump relay, MAF burnoff relay, and possibly the secondary fan relay(?). They all use the same Delco Relay or equivalent except for the fuel pump IIRC which has it's own unique part number. I would trace the fan wiring from the fans back to the battery area and have a good look. The fan harness is a separate piece from the main harness and the relay will be attached to it at one end. 2 of the plugs go to the fan, 1 plug goes to the primary fan relay and the other plug attaches to the main harness by the battery and AC condensor inlet/outlet. The primary fan relay is the only one I've ever had fail on me. I replaced all the ones on my firewall with no change in primary fan operation.

 

I have looked everywhere possible. With a very bright light. I have a fuse 20 amp Adjacent to the battery. The other area where you sent a photo of a relay there is not one. There is only one additional relay that is like the same shape as the ones at the firewall. It is located directly next to the air compressor. I’m assuming it’s for the air conditioner it does have a different number on it and then the other three, the other three are identical part numbers. I followed the wires off each motor that lead to a large wiring harness that goes over the middle of the engine and then appears to lead to the other three along firewall at the driver side. I don’t know where else to look

 

Also just an FYI the wiring harness you sent is till year 1989. I have a 1990 with speed density not a mass airflow sensor perhaps the wiring harness changed due to that. I appreciate your help but it’s not there

 

sorry man I thought I had it sorted out for you. Your profile says 1989 IROC-Z convertible but OP says 1990. I assume the fan harness did change as that one is listed for 88-89 only. Does the primary fan come on in diagnostic mode by jumping the 2 pins at the OBD connector? If not I still think there's a bad relay buried somewhere but I've only battled this on an 89.

 

His 1990 305 (MAP Sensor ONLY) should not have the 2 MAF Relays...
Unless the Car has been Modified.

The Relays on the Fire-Wall by the C100 Connector (near Brake Booster) would not be for the MAF or MAF Burn-Off Circuits.

 

Also if somone has the Specific (to the OPs Engine RPO) Schematic...

Can someone clarify if the Primary Fan is ECM with Coolant Sensor (5v Reference) Controlled...
Or just uses a Sending Unit (Thermostatic-Switch to Ground)?

 

I do not have a 1990 MAP 305 Schematic available at the moment...

The closet Schematic I can obtain right now is for a 1992 MAP 305.
It shows that the Primary Fan is ECM with Coolant Sensor (5v Reference) Controlled.





Look in the Bottom Right Corner for the section with the Cooling Fans.

 

Does the fan come on aldl jumpered ?

 

yes the on should be 108c off 105c with stock calibration chip assuming this is tpi

 

yes I can get the driver‘s side fan to turn on by jumping at the computer terminal under the dash. The top two right pins make it turn on

And I haven’t been on this page since I had the 89 this is a 90 with a speed density instead of the mass airflow

 

i’m not sure what you mean, if I jump at the computer under the dash I can get the driver side fan to come on.

 

Your description was confusing if you jumpered the aldl or at the ecm grounded the green/white. Might observe cts reading on scanner or tunerpro rt.

 

Sorry all the abbreviations are leaving me in the dust. I jumped it underneath the steering wheel where you would plug in the diagnostic tool to check the car out. I did not jump it at the computer.

 

Aldl=Assembly Line Diagnostic Link
cts= coolant temperature sensor



might measure the ohm coolant temp sensor engine. Sensor front of the intake yellow and blk wires. If at 100-120 ohms fan should kick on.

 

Seems like a lot of people are having all different kinds of problems with fans. This is the 3rd post ive put these in. 1990 tpi fan wiring

 

I was thinking if you link the green/white relay control wire to the grey relay control wire it would make both fans work if either of them are commanded on

 

It is my understanding that there are 2 coolant temp sensors. One is for the gauge and the other feeds data to the ECM. If you have the ability to see a data stream you can verify the function of the ECM CTS. If the fans operate with the computer in diagnostic mode I think that would eliminate a bad relay. Either the engine is not getting up to the required temp to trigger the ECM to call for fan or the CTS is not functioning properly.