Odd fan problem
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Racer
Joined: Aug 2013
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Odd fan problem
I have just done a tpi swap in my 84, and have a problem with the fan running any time the engine is RUNNING, but not with key on engine off. It will also come on when pulling codes with aldl. With help from Mr ******, I have replaced a bad ecm, and installed a new prom. The fan turn on problem is present on the bad ecm, the new ecm, and both proms, so it must be a problem with my wiring. I had to run my own wire from pin C1 of the ecm to the fan relay, and it has no shorts or problems, so I am left with a possible improper input to the ecm? Using a scanner (and also checking the pins) the a/c input is not causing it, and I am all out of ideas on what to check now. Doing a search did not bring up anything like this, so I am hoping someone has the simple answer I am overlooking, lol.
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Racer
Joined: Aug 2013
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7165, I just got it from Mrwillys. My old ecm(also 7165) was not communicating with my scanner and totally weirding out when pulling codes, but the engine would run. This ecm works perfect, I just get the fan on when running. I have already ruled out the normally closed relay possibility, as I still have a ground signal from pin C1 when past the fan turn on temp as seen by the ecm from the cts.
Last edited by nobodycls; Dec 6, 2013 at 07:36 PM.
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Racer
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This is weird, I have a reply that shows up on my e-mail, but not here. (some of this site looks different than it did a few minites ago, too.) It is about the mech. fan switch, which I no longer have. All wiring, sensors, etc. have been changed over to 87 wiring, and the relay has been properly connected to the ecm via pin C1 and 12 volts with key on to the opposing side of the coil in the relay.
Last edited by nobodycls; Dec 6, 2013 at 07:44 PM.
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
Can you scan the new ECM?
Two possibilities come to mind:
The ECM thinks the coolant is really hot so it turned on the fan. That would be the CTS on the front of the intake manifold. Pin C10 in the ECM. Try unplugging it -- that would tell the ECM that the coolant is cold. You still might have a short to ground on that wire, which would tell the ECM that the coolant is very hot. Usually a scan will show 304° F if the connection is open.
The ECM thinks the AC is on. There is a switch for that in the high pressure line. That's pin D11. That switch is normally closed and goes OPEN when the AC is on. If you have that connector, then unplugging it and shorting the contacts of the connector together should shut off the fan (if this is the problem).
Two possibilities come to mind:
The ECM thinks the coolant is really hot so it turned on the fan. That would be the CTS on the front of the intake manifold. Pin C10 in the ECM. Try unplugging it -- that would tell the ECM that the coolant is cold. You still might have a short to ground on that wire, which would tell the ECM that the coolant is very hot. Usually a scan will show 304° F if the connection is open.
The ECM thinks the AC is on. There is a switch for that in the high pressure line. That's pin D11. That switch is normally closed and goes OPEN when the AC is on. If you have that connector, then unplugging it and shorting the contacts of the connector together should shut off the fan (if this is the problem).
Thread Starter
Racer
Joined: Aug 2013
Posts: 301
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Can you scan the new ECM?
Two possibilities come to mind:
The ECM thinks the coolant is really hot so it turned on the fan. That would be the CTS on the front of the intake manifold. Pin C10 in the ECM. Try unplugging it -- that would tell the ECM that the coolant is cold. You still might have a short to ground on that wire, which would tell the ECM that the coolant is very hot. Usually a scan will show 304° F if the connection is open.
The ECM thinks the AC is on. There is a switch for that in the high pressure line. That's pin D11. That switch is normally closed and goes OPEN when the AC is on. If you have that connector, then unplugging it and shorting the contacts of the connector together should shut off the fan (if this is the problem).
Two possibilities come to mind:
The ECM thinks the coolant is really hot so it turned on the fan. That would be the CTS on the front of the intake manifold. Pin C10 in the ECM. Try unplugging it -- that would tell the ECM that the coolant is cold. You still might have a short to ground on that wire, which would tell the ECM that the coolant is very hot. Usually a scan will show 304° F if the connection is open.
The ECM thinks the AC is on. There is a switch for that in the high pressure line. That's pin D11. That switch is normally closed and goes OPEN when the AC is on. If you have that connector, then unplugging it and shorting the contacts of the connector together should shut off the fan (if this is the problem).
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Racer
Joined: Aug 2013
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Cliff Harris - You are awesome! I put a jumper in the high pressure switch connecter and the fan works perfectly, turns on and off at the temps Mr ****** set, and apparently, that was also preventing high idle at cold startup, too. Before it would idle at around 600 no matter how cold at startup, which made for a lumpy idle, but now it idles at around 1200 till it warms a little then starts dropping. (it is in the 20's right now) Now everything seems perfect, and I can't wait for the roads to clear up for a test drive. All of you guys on here are really great. One good thing in all of this - even though my diagnostic skills need some more work, at least my wiring was right, lol.
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Thread Starter
Racer
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Yeah, that did it. It never occurred to me that it was a normally closed switch, or that it would do anything without the a/c on input as well.
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Thread Starter
Racer
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GJ Cliff