Another cooling fan question
Thread Starter
Staging Lane
Joined: Oct 2020
Posts: 86
Likes: 7
From: St. Louis MO
Another cooling fan question I purchased a 95 z28 M6 car last summer. The cooling fans were not working, I tracked down "operation" to a separate relay had been wired in for function. I kept blowing the inline 30 amp fuse on this relay. Long story short, I wired in a heavy duty (35amp) switch with a 30 amp fused power lead to turn the fans on. I checked with a clamp meter and start up current draw was 27amps and operation was 17ish amps. So I'm thinking a relay isn't needed. My question is.. since I unwired the water pump temp sensor will the pcm run in open loop at all times now? And if so is there a way to wire around this? Also I tried shobox recommendation of tapping into the wire loom to ground the relays but that didn't work. I'm assuming because of the previous "modification" done for cooling fan operation. Thanks for any insight.
TECH Veteran
Joined: Dec 2008
Posts: 4,145
Likes: 61
From: Little Rock, AR
You need the water pump temp sensor hooked up. The PCM needs to know the coolant temp for proper fueling. With no sensor, it's going to be running over-rich all the time. Not good for fuel mileage or cylinder wear.
Since you bypassed all factory fan control, the 35A switch is good enough without a relay (since you verified current draw). A low amperage switch is what gets people in trouble.
Since you bypassed all factory fan control, the 35A switch is good enough without a relay (since you verified current draw). A low amperage switch is what gets people in trouble.
Thread Starter
Staging Lane
Joined: Oct 2020
Posts: 86
Likes: 7
From: St. Louis MO
Thank you sir. I read somewhere that without a temp signal that the PCM would be running in open loop. Just wanted to confirm what i read was correct. I'll look in the FSM and see if i can't find the wiring diagram and get something wired back up. Thanks again
Thread Starter
Staging Lane
Joined: Oct 2020
Posts: 86
Likes: 7
From: St. Louis MO
So basically some real time data would be the confirmation needed to assure proper fuel mixture? Any suggestions? tuner cat, data master? I have an innova scanner with real time but i believe it is only obd2 compliant.
TECH Veteran
Joined: Dec 2008
Posts: 4,145
Likes: 61
From: Little Rock, AR
If it is not hooked up, the PCM is going to see -40 degrees all the time.as the temperature. If you want to use a laptop, Scan9495 is free and a good program. If you wan to use a scan tool, any OBD-I EXCEPT Innova (they have a known problem and give erroneous results for the LT1).
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Thread Starter
Staging Lane
Joined: Oct 2020
Posts: 86
Likes: 7
From: St. Louis MO
Thanks Shbox. That's kind of what i got from the FSM. Wouldn't this throw a SES light with a DTC 15 tho? I have no SES light now. If i can run down the yellow(5v) and black(ground) wires in the harness, i'll wire them back in. I found a picture from you on the internet and it appears the wires should be in the harness on the right side cylinder head? I don't see any cut wires but i'll open up the harness today.
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Staging Lane
Joined: Oct 2020
Posts: 86
Likes: 7
From: St. Louis MO
So i found the factory connector. It is still connected to a ECT sensor that is just tucked up on top of the WP. Do you see any problem with driving the car "as is" for now? I will get a new AC delco sensor and connect it as designed. Thanks again shbox i appreciate your time bud.