Hi, at the risk of being redundant I have to ask a couple questions. I have a stock 86 iroc 305 tpi with a single fan. The fan used to work. My car heats up in stop and go and idle conditions. Open road it runs fine. By hot I mean 240+....shut it down and wait hot.

I have read through a bunch of different threads and keep seeing "check the cooling fan switch." I looked between 6 and 8 and I don't see anything there. Does my car have one somewhere else? I am thinking I will just replace the relay. Of course I read that its on the fire wall and next to the radiator. Where is the relay? Do they both control the fan? The one next to the radiator has a d. gr/white wire I can ground to get the fan to come on.

Oh and I turned my a/c to on position even though the compressor is unhooked and no fan action there but if I ground the diagnostics terminal it comes on.

Someone who knows whats what give me a clue...thanks

 

The ecm grounds e8 to command on the fan, The fan turn on is based off the ect next to the cold start timer switch in the front on the intake manifold. The ect or ect wiring maybe the issue or the ecm or ecm ground behind the passenger cylinder head. If you can use a scanner or data logger you can look at the ect the fan will be commanded on around 226F. The only other thing you can do is test the ect before you throw a ecm at it. Here is the resistance vs temperature.

If you ground the dark green / white wire at the relay the fan will come on with the key on engine off. Your fan relay is the center relay next to the master cylinder on the bulk head.

 

I tested the coolant sensor last fall because I also have an intermittent issue with a high idle and the ohms seemed to be right on. I tested cold and warm and the values looked correct. During my recent inspection of the fan issue I unplugged the coolant sensor (on the front of the intake..and yes I do know which one it is) and the connector broke when i went to plug it in. My car set off code 14 and I replaced the pigtail (so now its gonna be harder to test the ohms on that cts because I used the spare pigtail). I unplugged the battery and the code went away and didn't come back. After a 50 mile drive it only flashes 12.

I will look at the firewall relays but what is the relay on the pass. side of the radiator then?

 

I know for sure the 85 was next to the radiator so the 86 maybe as well.

 

Im wondering if I have an ecm issue. It also likes to idle at around 1500 rpms from time to time. Only does it when I drive somewhere, shut it off then come back out and start it up again. Sometimes it doesn't do it. Otherwise this car is great. No hacked up wires and everything else seems to work fine.

So the ground is hooked to the head where the ground strap is? Or is that what we are talking about? Its kinda hard to see back there. I am probably gonna have to take it to a shop. I don't have the right diagnostic tools to check the ecm readings and values.

 

yes there should be a ground strap on the back of the pass cyl head and the ecm, tps, mat all ground there.

 

One more question...could my relay be bad even if the fan comes on with the a and b terminals grounded in the diagnostic port?

 

a relay is a low current controlling a high current draw. There is power on one side of the coil and the ecm controls the ground. when the coil is energised the pole moves sending power to the positive side of the fan.

 

well something is wrong and I can't find a bad ground and now I know its not the ecm. I dont have a scan tool. I'm just gonna take it to a shop. I hooked up a ground toggle so I can run the fan. I'll post when I get the problem resolved so anyone else who has this issue can get some resolve too.

 

9 times out of ten this is a coolant sensor or pigtail issue. i would assume a bad wire considering your intermittant high idle issue. i would trace the harness back taking a reading every couple inches till you find a change in the readings

 

Ok, this is an elementary question...I really am smart but how do I test the wire with insulation on it? Poking it could gain me access to the wire but that would hurt the wire, right?

 

back probe with a paperclip or safety pin.

 

this or just poke it, your going to be stuffing it back into the harness so it's no big deal

 

poking the insulation will cause you problems down the road when moisture starts to corrode the copper wire.

 

Hey tuned, I took it into a shop. They think I got a bad ecm. Everything is reading correctly but the ecm won't engage the fan. The mechanic said he can do it all the way to ecm so it's not bad wiring. However he tapped the ecm and it dropped my idle (which is also an issue) and the idle dropped. Could a prom chip go out? Just a theory. Nothing had changed when I installed the new ecm so I don't feel that the problem

 

Prom is not normally an issue. Its most likely the ECM. There was issues with the early ECMs where the board fails due to the coating starting to come off. An ecm is about 90 bucks at advance and you plug your prom into it and if that's the issue it will he all fixed. If it is your prom you will have to do some hunting. I am not aware if you can buy a new one anywhere but if you find it its sure to be expensive

 

if he grounded the ecn pin e8 and the fan came on it sounds like the ecm isnt commanding it on. the ecm uses the input from the cts and in most memcal calibrations turns on the fan at 226F. You could see this being commanded on bye hooking up a aldl cable to your computer and using tunerpro with defintion $32. A cts is relitivly innexpensive gm 19187357 acdelco 213-4396. the only memcal calibration that was problematic for 86 drivilibility was aum.

http://www.gmtips.com/3rd-degree/dox/tips/ecm/prom.htm

 

I talked to the mechanic today. He did check the cts and it is giving correct readings to the ecm. They have all the correct tools to diagnose efi systems, thats why I took it in....I don't. He told me this morning that he performed a "tap" test on the ecm and the fan came on and the idle went down. Since the ecm is only a month old, he is gonna warranty it out with the part store and try a different one. If that doesn't work, I think the prom might have a bad solder or something. He was thinking the same thing.

In the meantime (in case i need a prom chip) what would be a sufficient chip to run? I'm sorta looking at a hypertech street runner. I don't wanna spend alot on a chip for a stock 305. I would rather save money for real upgrades later on.

 

I would try to source a stock 305 prom. Those hyper tech chips only lower the temp the fan kicks on. But in order for it to work right you will have to go to a lower temp thermostat. IIRC 86 is special as in it has a specific ecm but I can't remember if the prom is specific or not

 

You can run any tpi 305 automatic memcal mask $32, $32B or $6E although the 89 $6E is the best calibrations fdor the 1227165 ecm it has the vats enabled in the programing. If the prom is faulty the ecm will go in limp home mode and the fan will come on.

 

The mechanic called me. He put in the replacement ecm and the fan is coming on so thats good but the idle is still unreliable. What it is doing is just not closing the iac valve after the engine starts. well, when it does the high idle thing. Otherwise the car starts and idle adjusts normally. The idle jumps up slightly when the a/c is turned on and when its put in gear which is what its supposed to do. He can't find a thing wrong. No bad grounds, no vacuum leaks, no bad sensors. Thats why we are wondering if there is just a loose solder or something. 3 ecms can't all be bad. the only thing left to question is the prom. Its not burned up or anything so it may not be faulty enough to put the car in limp mode????

 

when you refer to memcal mask as $32, etc, is that the program of the prom?

 

yours is a definition $32 mask That is how the firmware and calibration is referred to. Did you have him look at the letters on top of the memcal to see if it is broadcast code AUM ?

 

No but when I get it back I will pull it out and check. i could call him but I'm sure he has other stuff to do.

 

Id replace the 27 year old $35.00 IAC valve and reset it. At least the ECM has something new to work with.

 

I already replaced the iac valve, twice (thanks autozone).

 

pull the prom out and get us the code

 

It was the prom. Got another one programmed from tunedperformanc and my car idles exactly how it should.

 

I think putting in the gallon of ranch dressing in the tank lettiuce help too