Bought Trans Am - Has 305 TPI on top of 350 block. Runs rough and had leaking valve covers which caused smoking. Changed gaskets and put in Fel Pro gaskets. Also, had pulled prom and was going to attempt to read with new GQ-4x4 programmer and started that process but decided to put it back into the ECM to run the car after changing gaskets to check everything. Started up and now radiator fan runs constantly. At first I had a pinched wire under the passenger side valve cover. Thought that was the problem but I freed that up and inspected wire and it was fine. Still have problem. Pulled connector from fan relay and the fan shuts off which is obvious if I understand the circuit correctly. It is my understanding that the 1986 does not have a fan switch but gets the signal from the ECM. Also I have two proms coming that I bought off ebay - one is for 1986 305 TPI and one for 1988 350 TPI. I hope to change out injectors to 22lb with ESC, prom, knock sensor, etc to fully utilize the 350.

Right now I plan on buying a fan relay. If that does not work it would be the ECM right? Would changing the prom fix that?

 

Do you have ac ? Is this in a f body or conversation?
the reason I ask about ac is no,nc pressure switch setting in the tune.

 

It has AC. It does not work. I have not looked into that yet.

what do you mean when you say “the reason I ask about ac is no,nc pressure switch setting in the tune.”?

 

The fan relay could be stuck or you have continuous power to relay...

 

Am I right in saying that the continuous power to the relay would be an output of the ECM? Is that a setting contained in the prom of the ECM?

 

3rd gen F body

 

You need to check the voltage at the relay whether it has 12 volts going to the radiator fan...I would troubleshoot the problem instead of buying parts you don't need...Just had a problem with the radiator fans on my 89 Iroc it was the 12 volt wire coming off the battery fuse link... I could bend the wire and get voltage intermittently...I spliced the wire and made a new connection and now the fans are working as they should...

 

Go to austinthirdgen.org and click on tech articles troubleshooting the cooling fan circuit...that will show you how to troubleshoot the radiator fan circuitry...Also great articles here at thirdgen...Hope this helps

 

try grounding d11 at ecm here’s a schematic of the fan

 

I 100% had this same problem. Replaced relays. Did all the checks. It was a faulty ecm. Sent it to Delco. Plugged it in and no more constant fan running. Works as it should

 

Do you know if it was an eprom issue within the ECM?

 

You get no information back when they send it back to you. Was 220$ i think.

 

Could be the ac pressure sensor wire is disconnected... its in the hard line on the frame rail. Even if the ac doesnt work / has a charge, if you disconnect that sensor, the fan comes on.



On my 87, the fan always ran. its controlled by the ECM, not a temp sensor in the head

But thr wires going to the fan relay connector were corroded and touched causing the fan to always get power.

 

Can you post a pic of the ac pressure sensor?

 

https://www.thirdgen.org/forums/cool...re-switch.html

iirc this is it, but like I said can just check if open or grounded at ecm d11.

 

Its on post #10 on Tuned Performances link...might be called ac fan pressure switch...I can;t recall.....

It's a little buried under the hoses / harness on the passenger side... its on the hard line that goes from the evaporator to the condenser. ... theres a I think black and blue wired connector that goes to it. On the 82 - 87 cars its right along the frame rail.. on the newer cars its raised a bit because of the evaporator design...


If its dis connected or the sensor is missing cause ac was taken out or something.... the fan should constantly run

 

 

I just got these offf the internet

 

Problem ended up being the EPROM. Changed it out and problem gone.

 

prom rarely loose data, if you swapped to a different calibration the normally open or normally closed setting was probably different based off year usage .

 

I agree about prom rarely being the problem however It may have happened when I put the prom in the programmer and attempted to read it. After that I placed it back in the ECM and the fan issue started. I had bought another prom that was supposedly the same year, same engine and replaced it and the problem disappeared.