Hey guys first post on the boards. I just bought an 88 L98 IROC-Z, that seems to be in great shape.

I've been repairing some of the gremlins the previous owner left me with. The cooling fans are puzzling me.

When I got the car, I noticed the aux. fan came on immediately with the key.

I found that the previous owner had placed a wire from the (tan wire) ignition switched pins on the aux fan relay connector to the (black/red) motor wire. He then taped over the connector and tucked it up into the relay housing.

I figured there had to be a reason for this, so I started using a v/ohm meter and jumper to test leads and functions.

1st: The Orange (always hot) lead was good, so I jumpered it to black/red and the fan came on. Not a necessary test, since I knew the fan was coming on with the key.

2nd: With key off, I tested green/wht and in the case of the 88, the tan ignition lead. Both had no voltage.

3rd: I turned on the key and as expected I found 12v on the tan wire. What wasn't expected was the 12v I found on the green/wht wire.

I thought this should be an open or a ground, thus the question in my subject line.

Checking down the line, I pulled the AC pressure connector. And ran the same tests as before, With the same results. Also, found 12v on the AC pressure connector grey wire with key on.

I haven't made my way down to the fan temp switch between #6 & #8 plugs, behind the AC and smog eq. etc, (sheesh that's tight) and maybe that is where I'll find some odd wiring that is the source of the 12v.

What really puzzles me is a comment and I'm quoting from the URL posted below explaining testing for the primary fan and it having 12v present on the until the ECM driver turns on, but this is on the primary.


"If the primary does not, measure the lighter guage or coil side of the primary with a voltmeter one of the 2 wires will have constant 12 volts with the key "on" and the other will have 12 volts until the ECM driver turns on. When it goes low the relay should click and the pri should run."

Looking at the schematics for the 88 aux fan I see it has a tan, then grey wire from the relay to the fan pressure switch, black wire continuing to the fan temp sw. and grey to pin D11 of the ECM.

Does D11 ever put out voltage? That seems opposite to what would be desired, since it would go straight to ground through the fan switch, if the motor was warm enough and the key was on.

Have any of you seen voltage on the tan pressure/temp sending wire coming to the aux fan relay at 'key on'?
Could this be one of those 'wire D12 to pin nnn' experiments gone bad?

Sorry for the long post, just wondering if I'm chasing the wrong issue.

Bill

https://www.thirdgen.org/techbb2/sho...&highlight=d12

 

ok guys, I'm still stumped on this. The fan switch, between plugs 6 & 8 is wired normally, and I've traced the black wire back to the front of the engine where it starts up toward the top of the block. (lost it in the jumble of wires, but I'll keep looking for it).

So far all of the wiring I can trace matches color codes so that's good. Tracing the wire in the looms is pretty much a PITA, I'm going to go to the ECM and see if there's something goofy there. I guess if it looks right and I can find a way to check for the voltage, on the ECM connector, I can at least isolate out that section of wiring.

Oh yeah, when I pull the FP/Fan fuse, with the key on, this odd voltage does not go away on the gr/wh wire. It does go away on the tan wire, as expected.

Again, guys, if anyone has seen something like this before, or thinks that there is some instance where 12v should be on the sensor/pressure switch side of the wiring, please speak up.

 

I'm guessing that since no one has responded with any ideas, that this is just an odd problem that nobody has heard of before.

The ECM connector and the wiring associated with it all looks completely stock. There are no visible jumpers, at least not in the wiring under the dash.

For now, I've separated the gr/wh lead about 6" before the wire connector to the relay. I ran a wire from a ground inside the car to a switch that I put beside the console. The wire on the other side of the switch is run to the aux fan relay wiring and is spliced to the gr/wh wire going into the relay.

This is not a permanent fix, but at least I've gotten past the previous owners wiring and I don't have the fan constantly on with the key. Also, I still have the option of activating the fan until I can really figure out what the problem is.

Again, guys, feel free to speak up on this if you've seen something similar or can think of something someone might have tried, that could be causing this.

Thanks.