Hi, I was wondering if there is anyone that may be able to guide me in the right direction, after reading many many posts regarding the cooling radiator fan (single motor) I haven’t been able to find the solution to my problem.
I have a 1986 Iroc Z28 305 TPI with bare bones options: No power windows, no A/C.
The radiator fan stays on at full power even when I turn on ignition without starting engine, the fan runs until I disconnect from relay ( next to radiator passenger side next to battery) I bought brand new relay and same thing happens I then replaced the coolant temp sensor in front of intake manifold with two wires (yellow and black ) that didn’t work either, I then replaced the gauge temp sensor on drivers side between cyl. 1 & 3, that didn’t fix the problem, then I looked everywhere for that radiator fan switch everyone talks about on passenger side next to starter but the only thing I found was the knock sensor with a single plug blue wire. The knock sensor looked old and corroded so I replaced that with a new one as well that didn’t help.
I also bought a new fan motor, that I replaced already because I read a post that said after replacing the fan motor all the gremlin issues went away but not for me.

Can anyone please guide me in the right direction? I have replaced many parts already except for the ECM, I’m not sure if my fan is controlled by ECM but there is no switch sensor anywhere to control it so will the ECM be the issue? I have been reading every post available and replacing all parts mentioned on those to no avail, any help will be appreciated.

 

Well, the Temperature gauge sending unit and knock sensor have absolutely nothing to do with your cooling fan, so that was time and money wasted.
The cooling fan thermostatic switch is in the passenger-side cylinder head (not the block, where the knock sensor is) between cylinders 6 and 8.
Try replacing that, or at the very least, check the wire and connector...

 

I looked repeatedly in the head as well in between those two cylinders but found nothing, there's no sensor in that area, I looked for many hours which only gave me the only option of finding the knock sensor and a hole that seems to have been plugged from factory. Please see attached pictures

 

This is the view of the cylinder head as viewed from the right/passenger side. The coolant temperature fan switch goes into the threaded hole the red arrow is pointing to between cylinders 6 & 8 toward the rear of the engine.



This is the view of the cylinder head as viewed from the left/driver side. The coolant temperature sending unit that runs the gauge in the dash goes into the threaded hole the red arrow is pointing to between cylinders 1 & 3 toward the front of the engine.

I'm a Pontiac Firebird guy into 1987 to 1992 Firebirds, Formulas, Trans Ams, and GTAs. I'm not sure how they did things on the Chevrolet Camaro side or on 1986 and earlier Third Gens. IDK if early non AC cars had one or two cooling fans and if they had just one cooling fan if it was ECM controlled or coolant temperature fan switch controlled.

 

If you don't find it in that head it is possible someone has "modded" your car. All bets are off at that point and it would be anyone's guess as to how to fix it.

 

The thing though is I've had the car since 2004 and it used to run great, the fan never did that until 2009 when the fuel pump went out and I didn't have it replaced until 2013, but the fan issue never went away. Then the car was put away in storage until December of 2024 and have been working on it ever since.

I also did a lot of searching and I have read several 3rd Gen Camaro posts that speak of the same issue of not finding a fan switch sensor in the passenger side and only a knock sensor. If I dont find a solution I may have to just install a fan controller like a Dakota digital or a flexalite.

 

Have you checked the FSM? Factory Service Manual. If you don't have one, I would encourage you to pick one up off of eBay.
But what I would do is review the wires at the relay, pretty simple setup, constant power, key on power, power out to the fan, and then the temp switch ground. Find that wire and started tracking it back to where it goes...

 

See if you can follow the ground wire from the relay. It probably leads to a fan switch somewhere...

 

This is another post i found within this forum that say the 1986 model doesn't have a fan switch, does anyone know which wire out of the radiator fan relay is the one the creates the grounding for the fan to turn on? is it the green with white stripe? please see attachment

 

Zackly:

Look at the relay and find the grn w wht stripe wire. That's the control for the relay. Follow it and see where it goes. In addition to the 2 Big Fat Wires that carry the high power, there should also be a small brown, which is switched ignition.

Some of the various TPI cars did in fact use the ECM exclusively to control the fan. No switch in the head. Yours might be one of those, I'm not familiar enough with which ones did it how to be able to tell you. If so, the ECM would ground that wire, instead of a switch. You can measure the voltage on it and see if it's being let go when it's supposed to; will have 12V on it when it's not commanded, ground when it is. If the fan runs when it's not being commanded, unplug the relay and see if it quits; if so, the relay contacts are welded and you need one of those. If the ECM is commanding the fan when it seems inappropriate, check the coolant temp sensor; the ECM may think the engine is hot all the time, and is running the fan accordingly.

 

Thank you So much for that information, I thought I was going crazy, the fan does exactly that, it stops running as soon as I remove the connector from the relay, so by saying that " the relay contacts are welded" do i need to buy a new relay? the coolant temp sensor (in front of plenum) is new however I just ordered a brand new AC Delco one in case that the ebay one I bought and is currently installed may be damaged or defective.

 

Depends.

What's the voltage on the grn w/ wht stripe wire? If the relay is BEING TOLD to turn on, then changing it out won't make it work any differently.

 

I have a 1988 Camaro IROC Z 350TPI with the same problem. Fans where always on. Turn out to be a bad EMC.

 

Juanz28, thank you for that information, if you don't mind sharing how did you go about replacing the ECM, were you able to just replace it with an identical part number or did you have to have it programmed? If so do you have a programmer I can send it to?

 

LOL okay doom and gloom Jesus man calm your *** down. Even if a guy "modded" the car it's still a simple fix to get it back to normal. Grab a wiring diagram and trace the wire back, if it's cut fix it. Done. Man oh man it's guys like you that make coming to forums unbearable.

 

"Unbearable"?? I've been here 25 years and have beared it just fine. Lotsof differing opinions and approaches to troubleshooting problems with these cars, some better than others...

 

Start at the beginning. Don't jump to the worst possible conclusion before examining what's really going on.

What's the voltage on the grn w/ wht stripe wire?

ECMs definitely CAN go bad. However it's VERY rare. Not time to worry about that just yet.

What's the voltage on the grn w/ wht stripe wire?

 

Voltage with ignition turned on engine off is 12.43V and 0V with ignition off.

 

I'll be home around 3:30pm today. i was troubleshooting, other things and decided to swap the ECM sinnce I came across one at the pick your part. once I swapped the e c m.The cooling fans turned off. But when I get home
We can go over the wire diagram from ECM to coolant temp switch.

 

I see you are new here. Welcome to the forums.

 

Needs to be measured with it plugged in and operating wrongly. Back-probe the connector pins.

Not sure what you're measuring there; since none of the pins in that connector are ground, the number is a bit ambiguous to begin with.

Get the voltage from the grn w/ wht stripe to ground, with the plug plugged in, key on, and in screw-up mode. That is, WHILE IT'S IN THE ACT OF SCREWING UP.

 

85 and 86 TPI cars had a single fan and the fan was controlled by the ECM. If you have your cars HVAC controller turned to any AC setting - the fan WILL turn.

The "switch" you've heard and read about in the pass side head is specific to duel fan cars,,... that switch controls the SECONDARY fan.

The GREEN/WHITE wire is GROUND signal wire from the ECM to the Relay and should only show GROUND when cooling temp is over 230 (or so) degrees or the AC is active. If it shows GROUND any time the key is turned to RUN ( cold / no AC running ),.. then the ECM is grounding that wire when it SHOULDN'T.

Be sure that the 'fan pressure switch' is connected and test with voltmeter (or other tool) to see if/when the switch shows GROUND. This switch is mounted on the aluminum hard-line from the AC condenser to the AC accumulator.

I've owned more than 1 85 & 86 TPI with a bad ECM causing the fan to run at all times. While I have never seen your stuff,... the parts you've tried to replace and have been troubleshooting seem to indicate the ECM (or fan pressure switch) is suspect.

Here is the single Fan wiring schematic for the 85 TPI; 86 is similar but the wire colors changed a little..... Wire @ terminal "C" at the relay will be BROWN/WHITE, ( Not solid BROWN) and signal wire @ fan pressure switch is BLUE; ( Circuit # 992 as shown for 85.)


Good luck !

 

Thank you so much for this new information. Mine doesn't have A/C so I assume I don't have a fan pressure switch? So now it seems more obvious that the ECM is the culprit, is it hard to replace the ECM? Doni have to have exact same part number? Are there any steps I need to take to replace?.
I was also wondering if a bad ECM will prevent me from being able to set my timing, I tried doing the procedure of unplugging single wire plug on passenger side fire wall then started car and proceeded to set at 8 which seems to run better still high idle of 1000 to 1200rpm then shut car off tighten distributor and plug cables back together. As soon as I try to start the car it seems like the computer doesn't retain the timing and idle I had set, and it starts for a little then dies, I did this procedure various times where the car won't even move without dying if I put it in Drive. Will this also be a cause of a bad ECM? Thank you so much all of you for all your help.

 

Stop spanking off about that.

Put the car all back together. Take a deep breath. MEASURE.

WHAT'S THE VOLTAGE ON THE GRN w/WHT STRIPE WIRE when the fan is running butt isn't supposed to be? In other words, catch it WHILE IT'S IN THE ACT OF SCREWING UP, and see if (a) something - the ECM, some PO wiring hack, WHATEVER - is commanding the relay to operate; or, (b) is the relay operating the fan even when it's NOT being told to do so?

Throw all the rest of that away. Resort to the last refuge of the incompetent (well, ... not violence, ... just, ... LOGIC) which I am uniquely qualified to speak to, being INCOMPETENT myself, and take your last refuge in REASON. Being a total dumba$$ myself, that's the only way I can ever fix ANYTHING.

What's the voltage on the grn w/ wht stripe wire, WHILE IT'S IN THE ACT OF SCREWING UP?

 

The green with white stripe wire reads 0.13v when ignition on and fan running I used ground from engine where the negative cable from battery is mounted.

 

So yeah, it's being commanded to come on.

Either the wire is shorted to ground somewhere (deliberately or otherwise), or the ECM thinks the engine is hot, or the ECM is bad. With the voltage that far from zero, it's probably not a short in the wiring.

Try unplugging the CTS. Check its wires carefully as well; if they're shorted together, the ECM will think the temp is about 400°, and will run the fan to try to cool it down. If unplugging the CTS turns off the fan then the CTS is bad.

 

Thank you Sofa kingdom, I will try doing that tomorrow.