MSPNP fans come on with key even when dead cold.
 

Alright guys, I've got a 90 car with a 99 motor running off a MSPNP. Recently after having my battery hooked up to my DD's charging system to recharge it (94 integra) I forgot it was hooked up and cycled the key on the miata. As soon as i turned the key on I heard the fans kick in which they have not done before (unless the motor was hot, of course), and i realized what i had done. Turned off the key asap.

Since that incident anytime i turn the key on the fans come on. I first suspected a fan relay, but tested this (i think). I pulled the ECU from the car and cycled the key on, the fans DID NOT come on. If the relay was stuck the fans should have came on with or without the ECU in place (i think).

Now I've also tried disabling the output 2 in megasquirt. Output 2 is the default fan control setup for the MSPNP, i disabled that output entirely but the fans still run. Even with the output disabled in the software the "output 2" stays lit up in Tunerstudio at the bottom.

I'm thinking maybe i fucked something up on the megasquirt board itself, but the ECU works perfectly otherwise and my car is running GREAT.

Any ideas at all ? This is really pissing me off and I'm about to setup an external relay/switch for my fans and go that way if i cannot find a solution.

Here's my current MSQ if that helps. Note that even when i completely disable the output it still runs.

It could be the thermoswitch has gone bad - if the thermoswitch fails open, the MSPNP can't turn the fan off.

Thanks for the tip. There is NO thermoswitch on the system since I've gone to the 99 motor. I removed it and was going to let MS control the fans via the CLT.

I had this happen and eventually realized I had wired that output up incorrectly.

What I had done was wired PA0 on the mainboard directly to 1L on the connector board, rather than wiring PA0 to relay 1 input, and relay 1 output to 1L. This is because I can't read and am stupid. If you also can't read and are stupid, perhaps it is what you have done. If not, maybe it'll give you some troubleshooting ideas.

Thanks for the ideas! This issue is on a MSPNP where the fans have been previously working fine. I am starting to suspect something on the board itself though..

My MSpnp1 did this so I switched to JS2 for the fan switch and then it acted "less strange".

Now we're getting somewhere. It might be asking a bit much, but how is this done? I'm assuming you can reassign outputs without rewiring it? It sounds like I should try a different output to test at the very least.

Anyone else with any ideas? Can't DD the car until I fix this. Thinking about wiring in an external thermoswitch to control my fans now..

I tested the relay, checks out. I tried plugging back in my front fan switch, made no difference. I can get the output in the ECU to show as "off" in tunerstudio at the bottom by playing with the settings, but the fans (both of them) never turn off.

I think the key here is that BOTH fans are turning on. Unless you've altered your wiring to run them in parallel, this only happens when the A/C relay is energized by the ECU. The A/C relay is energized by a Blue/Black wire going to pin 1J on the ECU. Within the MSPNP, I think the daughter board directly routes this to pin 1Q (Light Green/Black wire going to A/C thermoswitch). This wire gets pulled to ground through the A/C thermoswitch, A/C switch and blower control switch in series.

Anyway, look for shorts to ground on 1J and 1Q of the harness connector. More than likely, it will be a short on 1Q since plugging and unplugging the MSPNP makes it go away.

If you don't already have it, grab the 90-93 Field Service Manual from the sticky so you can identify the correct pins.

Thanks Hornet! Going to have to check that out soon. I just pulled the A/C relay altogether and both of the fans still come on, which seems quite strange to me.

Edit: in fact, when i completely unplug the a/c harness before the relay the fans still come on.

I had a similar problem once, but that was caused by the Fan output and the Tacho output being configured on the same pin (JS0). The fact that the tacho output was on caused the fan to always run, and eventually burned a few relays (and they're expensive as f***).

Maybe you could've messed around the settings or something? Worth a check!

That tells me that your wiring isn't stock. Someone along the way has wired both of your fans through the fan relay. Both of those relays (cooling fan relay and A/C relay) are on the power side of the fans.

Oh well, sorry.

Nevermind

The good news is that if it is in the MSPNP, it should be on the daughter board and those are through-hole components. If Hugo's suggestion doesn't pan out, might be time to open the MSPNP and see if you've let the smoke out of anything.

Didn't you recently do some trickery inside your MSPNP? Maybe you have a solder bridge somewhere.

Great suggestions everyone, i really appreciate it. Going to go through and do some more checking with both the settings and the MSPNP daughter board.

AFAIK the wiring is stock, but it sounds like you don't think so. Interesting. I did to the VTPS mod, so i'll check over that (but i was pretty careful about solder bridges, AND the fan issue didnt happen right away after the mods).

On a 90-93 with stock wiring in good condition (no shorts), the ECU cooling fan output (to the cooling fan relay) only activates one fan. The ECU A/C output (to the A/C relay) activates the A/C clutch and both fans.

Wiring diagrams are your friend.