LonghornSS

Guys I did a search on here but was unable to come up with a concrete answer.
I currently have two Project cars with the 425 HP E-Rod package in them (ECM 19257232)

The fuse panel is only wired for one fan but both projects are using two fans, I do not want both fans coming on at the same time because I do not want the spike in the electrical system from 2 fans coming on at once.

The fan relay is being triggered by two wires from the ECM. I know that the blue and green wire coming from C1 54 and C3 49 respectively in the ECM are what are triggering the single fan relay in the fuse box the blue and green wires are connected together to one pin on the relay. Can I separate these two at the (fan one) relay and simply wire in an additional relay in and empty relay section of the fuse panel for fan two? Green Trigger to one relay and blue trigger to the other?

Also is there a way to wire up the fan circuit to an aftermarket a/c (Vintage Air) trinary/binary pressure switch so that the fans come on when the A/C requires it? I am thinking just use the ground side of the trinary safety switch and wire it parallel with the ECM Blue/Green triggers?

DW SD

Yes you should be able to wire in a separate relay to drive the fans separately. The ecm may need to be tuned to adjust on off temps for both fans.
I use s trinary switch to trigger my fan too. In that circuit I ran a second relay in parallel to drive the fan. If you just use a ground trigger from the trinary to drive the existing fan relay you will trigger a fault code on the ecm when it sees the path to ground provided by the trinary switch.
I use a bus bar to tie the two relay outputs to the fan






You can (barely) see the bus bar in the bottom left of the fan shroud. Middle bottom of picture.



Finally, there may be times when both relays are energized. I see no issue with this my fan does not run any faster as I used sufficiently large wiring.

I hope this helps.

LonghornSS

What you are describing about the two separate ecm driven relays is exactly what I was thinking would need to happen.
If I am in the computer changing fan temps could I not just turn off the MIL function for the fan error? I know if my fans don't come on I could have an issue and having that MIL light could alert me to any fan issues.
I can get around this by adding an over temp warning to my Dakota Difital gauges.

Thanks for the input.

DW SD

I don't have the skills / tools to program the ECM, though I've had my single fan on / off temps adjusted (I have a Gen IV e38 ECM). I believe the two fans would be independently programmable. I suspect searching around will confirm or calling a local tuner.

You could also put a diode between the two ground triggers and ECM, so the ECM doesn't see the path to ground provided by trinary.

If it was me, I wouldn't fart around with disabling the MIL. i don't know if that'd disable the fan control circuitry in the ECM.

Adding another $5 relay and harness seemed the simplest for me. Actually, I added the bussman fused and sealed relay box, which was about $100 with mini relays and fuses already installed and the whole box pre-wired. Search around and you'll find that.

I used the relay box for the headlights, cooling fan, and any high current items in the engine bay and forward. This moved significant amperage loads from inside my cabin, reducing wire sizing requirements.

I think you could easily test, too. Just run the engine and put an ohm meter on the outputs to ground. Wait until you get close to zero ohm reading and record the temps. You'll know the ECM called for fan(s).

cheers,

Doug

LonghornSS

Doug,
Thanks again for the ideas. The GMPP fuse panel/relay center is plenty big enough and expandable for my purposes. I should be able to wire in the required second relay. I have the required terminals for the maxi fuse and and relay metri terminals.

The diode in line with the triggers and not removing the MIL is a good idea, although I do not think turning off the MIL in the computer would effect the functionality of the fans but I would of course have to proof that one out.

DW SD

Sure! It will also be easy to wire in a third relay for the trinary switch. But at least you have a plan you can test.

You would'n't need a busbar either, I suppose. You could just wire both positive leads (one from trinary and one from ECM triggered relay) to the fan.

I wanted to be able to disconnect my fan easily by unbolting it from the shroud and then disconnecting the wires easily.

I'm very happy with the SPAL fan. On startup, it draws over 30 amps. I had to track down a 40 amp fuse.

Did you consider the PWM fan controller as used on the corvettes? It is worth looking in to that if you like soft-start. I know Andrew posted some info about that on his build thread and on a thread about the PWM fan controller.

Many ways to do it! Good luck!

Doug

Dave Plummer

I'm a little confused, but very interested in the answer...

In my case, unless they're in the same insulated wire, there's only one fan trigger. I have no problem programming the set points and hysteresis and all of that, but without two actual wires coming out of the harness, what good is it?

Or are there still two wires in the eRod harness? Where do I find the second one? I stripped back the insulation on the big blue "C Fan" wire and it's a single wire... is the other available inside the fusebox or harness?