Fan kicking on only when I turn the key off and back on
 

I have a 85 z28 with the 305 tpi. I let it get to 3 quarters then cut it off and start it back up then the fan kicks on. I replaced the coolant temp sensor but didn't change anything

Re: Fan kicking on only when I turn the key off and back on
 

Wonder if your resetting the ecm with the key on and back off again.
Could be a bad ecm like your other post about high idle.

Re: Fan kicking on only when I turn the key off and back on
 

Yah this is the other reason I was thinking something is up with the computer

Re: Fan kicking on only when I turn the key off and back on
 

Any other ideas ?

Re: Fan kicking on only when I turn the key off and back on
 

Any wiring issues, fan switch inside the car ? Someone tap the relay to the ignition switch.
On most years the ecm controls the fan relay ( might be located next to the radiator( with a green/white wire.

Re: Fan kicking on only when I turn the key off and back on
 

His ECM flashes 12 codes fine and even stored trouble codes for stuff we know is wrong (EGR delete), and grounding the green/white wire on relay by rad kicks fans on no problem. Just FYI :thumbsup:

We think there was a fan switch hooked up in the car but flipping it does nothing lol

Re: Fan kicking on only when I turn the key off and back on
 

There is a relay wired to the neutral safety switch for some reason. There is also a switch in the center console it is ran to the relay on the firewall, its spliced in between the thick orange wire running to that relay.

Re: Fan kicking on only when I turn the key off and back on
 

That sounds like the Orange +12V constant line for the fuel pump relay, so now the question is what was he trying to power with the switch :crazy:

EDIT: might be red neck kill switch :crazy:

Re: Fan kicking on only when I turn the key off and back on
 

Yup kill switch to keep the pump from priming

Re: Fan kicking on only when I turn the key off and back on
 

I looked over the fan relay it appears to be fine. The connections had a bunch of old grease on them so I cleaned them up

Re: Fan kicking on only when I turn the key off and back on
 

Bump, tried a new ecm and the fan is still doing the same thing

Re: Fan kicking on only when I turn the key off and back on
 

Have you replaced the fan relay. Maybe the contacts are sticking. Not sure what else to tell you to try.

Re: Fan kicking on only when I turn the key off and back on
 

Actually just picked up one today but haven't tested it yet. Will do tomorrow

Re: Fan kicking on only when I turn the key off and back on
 

Welp tested it with new relay and still doing the same thing of only coming on for a few seconds when I let it get to about 3 quarters and cut the car off and start it again. I'm stumped.

Re: Fan kicking on only when I turn the key off and back on
 

How long are you keying off for? Maybe heat soak?

RBob.

Re: Fan kicking on only when I turn the key off and back on
 

I just cut it off for a second then start it back up and it comes on for a few seconds then cuts back off.
I just checked the relay wiring today and all seems good and fan fuse is good too

Re: Fan kicking on only when I turn the key off and back on
 

I think d2 of the ecm is fan control to the relay. This should be a green and white stripe wire. I’m wondering if it’s a bad coolant temp switch triggering the relay.Did you replace the one in front of the intake next to the cold start switch ?

Re: Fan kicking on only when I turn the key off and back on
 

Yes that's the one I replaced. Maybe the new one was bad ?

Re: Fan kicking on only when I turn the key off and back on
 

I wouldn’t think the cts is bad in the same manor as the first one. Is the wire from the ecm to the relay spliced . The other possibility might be a bad prom. You might have a code 41 or 51 if that’s the case. I can’t think of any other possibilities maybe rbob can suggest something.

Re: Fan kicking on only when I turn the key off and back on
 

[QUOTE=Tuned Performance;6194984]I wouldn’t think the cts is bad in the same manor as the first one. Is the wire from the ecm to the relay spliced . The other possibility might be a bad prom. You might have a code 41 or 51 if that’s the case. I can’t think of any other possibilities maybe rbob can suggest something.[/QUOTE

I couldn't find any splices in it when I looked it over and only code I get is for egr. Maybe it is the prom, I need to have a new one burned anyway to delete the emissions

Re: Fan kicking on only when I turn the key off and back on
 

The code 32 can be programmed out of the prom. The fan on should be set to 222f in the stock programming but can be changed too.
You might consider the 870 to 165 swap instead of investing in a prom.
It sounds like your prom is working if you can retrieve codes.

Re: Fan kicking on only when I turn the key off and back on
 

There should be a secondary fan switch in the cylinder head between cylinders 6@8.
I don’t see how this could cause the intermittent fan operation but the switch grounds the relays green/white wire like the ecm does for fan request.
Here is the schematic for the 870 ecm. I don’t see anything else that can trigger the fan other than the ecm and head switch.
https://cimg7.ibsrv.net/gimg/www.thi...0f9df9582.jpeg

Re: Fan kicking on only when I turn the key off and back on
 

I thought the 85 tpi didn't have the secondary fan switch

Re: Fan kicking on only when I turn the key off and back on
 

It says 5.7 only so it must apply to the corvette only.

Re: Fan kicking on only when I turn the key off and back on
 

So its only the ecm that grounds it. I can't think of anything else it can be

Re: Fan kicking on only when I turn the key off and back on
 

I found the coolant temp sensor connector was a bit broken and I think it wasn't making a good connection. I messed with it a bit and it fixed my high idle issue but the fan is still doing about the same thing. I did notice when I cut it off and back on the fan stayed on a little longer than before until it cut off