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Old 07-27-2005, 05:28 PM   #1
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Should the fan turn on when ignition is turned on?

I was just curious if this is normal. Someone told me it wasn't. I noticed that it does turn off though when i pull trouble codes. Any ideas? Thanks.
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Old 07-27-2005, 05:42 PM   #2
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if the ignition is on, AND the coolent temp is high enough, yes it should come on.


if the coolent temp isnt hot, no.. it shouldnt ALWAYS come on when the ignition power is on.
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Old 07-27-2005, 05:48 PM   #3
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Well it comes on EVERY time the ignition is turned on. What would cause this?
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Old 07-27-2005, 06:18 PM   #4
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someone hard wired it to the ignition
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Old 07-27-2005, 07:47 PM   #5
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is the ac on or off when u turn the key?
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Old 07-27-2005, 07:50 PM   #6
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AC is off. It doesn't really look like anyone messed with the wiring but it is possible. Not that it is a huge deal to have it running. I just don't want to burn the motor on it.
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Old 07-27-2005, 08:35 PM   #7
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my dads fan was hard wired and hes gone through 3 fans in the last 2 years. hope u figure it out.
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Old 07-27-2005, 09:10 PM   #8
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Where do i start?
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Old 07-27-2005, 09:22 PM   #9
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i would search for help finding the relay. i think its on the firewall somewhere. maybe it is stuck or had been removed. i would trace wires.
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Old 07-27-2005, 09:31 PM   #10
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i just found that its on driver's side firewall, by the master cylinder. It has 4 wires going to it. the fuel pump relay has 5 wires going to it. i hope this helps.
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Old 07-27-2005, 11:47 PM   #11
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Re: Should the fan turn on when ignition is turned on?

Quote:
Originally posted by trueburton
I was just curious if this is normal. Someone told me it wasn't. I noticed that it does turn off though when i pull trouble codes. Any ideas? Thanks.


Are you getting codes when you check them?
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Old 07-28-2005, 06:37 PM   #12
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Yes but thats a different post.
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Old 07-28-2005, 06:57 PM   #13
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any chance the plug for the temp switch is damaged? When I swapped my heads I left it unplugged and the fans would come on all the time.
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Old 07-28-2005, 07:07 PM   #14
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I am not sure about that. I geuss it's a possibility. Those are pretty cheap aren't they? maybe I'll just pick one up for sheets and giggles. Is that the plug that is like a 7/8" on the Pass side head and is a pain to get to?
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Old 07-28-2005, 07:20 PM   #15
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I meant the electrical connector itself. I didn't plug it into the temp switch. The switch was in the head.
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Old 07-28-2005, 07:24 PM   #16
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Oh i understand.
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Old 07-28-2005, 07:29 PM   #17
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any chance the plug for the temp switch is damaged? When I swapped my heads I left it unplugged and the fans would come on all the time.
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Old 07-28-2005, 07:51 PM   #18
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You either have an unplugged or btoken fan switch. It is located in the passenger side head. When damaged the fan comes on automatically as a safety measure.
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Old 07-28-2005, 10:15 PM   #19
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Quote:
Originally posted by ShiftyCapone
You either have an unplugged or btoken fan switch. It is located in the passenger side head. When damaged the fan comes on automatically as a safety measure.
thats something i havent heard of when trying tho figure out my dads probelm. a shop dropped a new 355 in like 2 years ago. ill try to find a picture of it to see if hes got one still?
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Old 07-28-2005, 10:24 PM   #20
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You aren't by chance leaving the A & B pins connected with the paperclip/etc. when you are turning on the car?
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Old 07-29-2005, 04:11 PM   #21
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No that would be idiotic
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Old 07-29-2005, 05:36 PM   #22
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I don't see how disconnecting the fanswitch wire, can cause the fans to run?

Fanswitch decreases in resistance when it gets warmer.

High resistance assumes colder. Ultimate cold would be an open/disconnected wire.

Someone care to explain how for me?
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Old 07-29-2005, 08:34 PM   #23
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From what I understand, as stated earlier, the fans come on as a precaution if they are disconnected. However my fan goes off when I start the engine until it warms up and then the fans kick back on as they are supposed to. I am a little confused.
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Old 07-29-2005, 09:01 PM   #24
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Somebody has to explain this "precaution" to me, and how it works.

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Old 07-29-2005, 09:10 PM   #25
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Nevermind, I'll tell you how the dual fan setup works....

primary is controlled via the CTS in the intake, sends the resistance to the ECM, ECM interpets for temp and (via ECM setting) turns on the primary fan.

Secondary fan is controlled via Fanswitch, also grounds the primary (on my '89 anyways) fan, energizes both relays and both fans turn on.

Also, A/C high pressure switch activates the 2ndry line on my '89, again, activates both primary and 2ndry fans.

There is no "fail safe" mode on my '89 (very, very, very similar to your '87.

In fact I have a 91RS TBI that...son of a gun...with the fanswitch disconnected doesn't energize the fan either.
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Old 07-30-2005, 03:23 AM   #26
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Quote:
Originally posted by slayer2000
any chance the plug for the temp switch is damaged? When I swapped my heads I left it unplugged and the fans would come on all the time.
That switch only powers the heavy duty fan, it is in parallel with the A/C fan switch. Assuming for now that there are no wiring problems, or bypasses. Leaving the temp switch unplugged removes it from the equaion. To ease the trouble shooting leave it disconnected.
First determine which fan is turning on, one, or are both turning on?

The following is possible:
1) One, or both fan relays have failed closed. The heavy duty fan relay is on the fender near the coolant resevoir, the primary fan relay is on the firewall behind the brake booster.

2) The A/C fan switch has failed closed only if the heavy duty fan is on with A/C off, and the ignition on. with the fan on unplug the connector, it's bad if the fan stops.

3) The ECM controls the primary fan, and it's fan solid state switch can fail closed leaving the fan relay coil connected to ground. No codes, no problems with the rest of the ECM.

4) If the ECM eprom has been changed, or reprogrammed the primary fan may come on with the ignition. When I updated my 1988 program with the 1989 $6E to delete the cold start system, I had to change the "Normally Open Fan Request Input" from closed to open because the program was for a 1989 Corvette.
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Old 07-30-2005, 11:08 AM   #27
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The weird thing is though that the fan comes on when I turn the ignition on. But it is not on once i start the engine. The fan will then later come on when engine warms up to like 200 degrees or whatever the stock setting is. So wouldn't that eliminate the possibility of a failed relay? Oh yeah it is the driver side fan that comes on.
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Old 07-30-2005, 09:15 PM   #28
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I have an indicator light on my 88, the fans do come on when starting the engine, go off pretty quickly. Never understood this either but it doesn't seem to cause any problems. The secondary sensor is a switch, on or off, can't imagine this having this effect when unhooked.
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Old 07-31-2005, 03:31 PM   #29
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Quote:
Originally posted by trueburton
The weird thing is though that the fan comes on when I turn the ignition on. But it is not on once i start the engine. The fan will then later come on when engine warms up to like 200 degrees or whatever the stock setting is. So wouldn't that eliminate the possibility of a failed relay? Oh yeah it is the driver side fan that comes on.
Driver's side is primary fan controlled by ECM. That would be item #4.
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Old 07-31-2005, 04:56 PM   #30
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Quote:
Originally posted by rgarcia63
Driver's side is primary fan controlled by ECM. That would be item #4.
Item #4?
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Old 07-31-2005, 04:57 PM   #31
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When I bought this car is was completely stock so I doubt the PROM was modified at all. Could it be something esle?
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Old 07-31-2005, 07:38 PM   #32
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Quote:
Originally posted by trueburton
When I bought this car is was completely stock so I doubt the PROM was modified at all. Could it be something esle?
So, the primary fan comes on when the ignition is initially turned on then, it turns off, and functions as it should when the ECM senses a hig temp. Unless the ECM is faulty, it's working as programmed.
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Old 08-01-2005, 09:43 PM   #33
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Yes kind of... it comes on when ignition is on, engine off. Then when I start the engine, it is off until the engine reaches High temp.
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Old 08-02-2005, 06:57 AM   #34
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Quote:
Originally posted by trueburton
Yes kind of... it comes on when ignition is on, engine off. Then when I start the engine, it is off until the engine reaches High temp.
That would be the case if the ECM switch "Normally Open Fan Request Input" is switched to closed, the EPROM isn't physically changed just reprogrammed. The only way to tell is to copy the EPROM to a binary file and use and editor to check it.

The EPROM in my '88 is OEM, but I erased it, and reprogrammed it with '89 ARP binary file. My fan is off with the engine off and comes on when I test for codes, you says your's does the opposite that's why I suspect the ECM firmware switch.
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Old 08-02-2005, 05:28 PM   #35
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Yes but as previously stated, When I bought my car it was completely stock. Not even nice spark wires or filters or any basic upgrades so I doubt that the EPROM was reprogrammed. But I geuss it is possible.
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Old 08-03-2005, 08:40 AM   #36
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Quote:
Originally posted by trueburton
Yes kind of... it comes on when ignition is on, engine off. Then when I start the engine, it is off until the engine reaches High temp.
Sounds like the ECM is bad. Tap on it while the engine is running, any stumbling or change in how it runs signifies a bad ECM. Which is common with the '165s.

Al.
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Old 08-03-2005, 04:35 PM   #37
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I have already replaced the ECM once and the car did this same thing since I bought it so I don't think it has anything to do with a BAD ECM. I'll try tapping it though. See what happens.
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