Kansas JoyRide

iTrader: (1)

Ok, my cooling fans won't activate at temp. I have a PFC and have set them to come on at 86C but nota. To date I have confirmed the wiring from the ECU to all the fan relays has continuity and every thing works if I ground the wire myself. Also turning on the air causes the fans to work. My thermo switch seems to be working (Miata) because the one fan comes on at 93C. And fan speed goes to medium if I ground the other two relays. I deduce the problem has to be somewhere between the temperature sending thermostat and the ECU.

So here is my question: If the commander is reading water temp, and it is, is that a confirmation that the Water temp sensor is good and there is no wiring problem between the sensor and the ECU. if the answer to that is yes does that mean the problem has to be with the ECU or is there another ground point somewhere that could be the problem?

DaleClark

iTrader: (55)

Set the ECU output to something REALLY low, that will make it easier to test. I think the Commander MAY show that as an output in the sensor check screen, not sure but worth checking on.

Find the output pin of the ECU that goes to the fan relay, I imagine it will ground when it's supposed to be kicking on the relay. See if that's the case.

I do believe the ECU uses the factory water temp sender at the back of the thermostat housing (the green 2-wire plug) to figure out when to kick on the fans.

Also worth checking to see if you have the fan recall harness installed, if something's bad with that that could cause problems. For more info on that check my big thread on how the fans work.

Dale

XLR8

iTrader: (52)

Per forum rules, please label your threads properly. It helps others in searching...

Now on to your problem. I would try replacing the thermoswitch with OEM, then the coolant temp sensor. As Dale pointed out, the one on the back is used by the fans. The Miata sensor may have an issue with the PFC. It's a long shot, but possible.

After the test Dale mentioned, If you had another PFC, it could be worth trying it to see if it was an ECU issue.

zayrx7

its your fan relay

DaleClark

iTrader: (55)

Actually, the fan thermoswitch (the one wire sensor) is a direct input to the fan relays and that seems like it's working as advertised. The ECU also has an output to the fan relays to trigger the fan, the green two-wire sensor by the fan switch is the main water temp input to the ECU, and that's how it can tell what temp it is and when to run the fans.

The Datalogit is the only way you can set the fan temps. There are 2 or 3 places to put the temp in, make sure they're all the same, only one of them actually works on the '93-95 style ECU/harness. The later FD's got rid of the fan switch and had the ECU control 2 fan inputs.

Bad relay is also a possibility.

Dale

Kansas JoyRide

iTrader: (1)

First, thanks for your replies and ya, sorry about the title, my bad.

The relays are all good. I have tested and some cases replaced them. If I ground the wire before the relay that activates it everything works as it should.

Dale I think you got it exactly right, the Miata switch is causing the #3 relay to activate at around 92 C, (this is a lower temp than the stock switch for the 93 which is why I am using it).

I replaced my engine wiring harness a few years ago and that is when I started having this problem. I get that that should make the answer obvious but I have traced all the wires and everything has continuity. that is what I don't understand. I have traced the wires to the ECU and measured signal from the relays to the ECU; everything is wright. I think you have confirmed that if the commander is reading water temp that is where the ECU would get it's data to ground the circuit so it looks like all that is left is the ECU.

A couple of other questions:

I see on the wiring diagram for the 4th plug-in to the ECU two pins that are labeled as grounds for sensors. Is it possible that the ECU is looking to one of those ground sources to ground the circuit and not finding a good ground?

Where are the other placed in Datalogit to set the fan temp? I am at work so I don't have access to my tuning laptop right now, but the only place I thought you set that is in the field where it gives the opportunity to sent the fans to come on low at x temp and medium at y temp and so on. If I remember right you set three temp in that field or maybe only two?

I changed my fans to come on at 85C, the idel raises 200 rpm as it should for Electical load, but no ground signal to the relays.

I wish I had access to another PFC to test it but no such luck. I am a poor boy in the middle of Kansas. I haven't even seen another third gen around here for years.

I am confused about what you are referring to when you say fan switch. Is there something other than the water temp sensor, the Air conditioning switch, the water temp switch (second probe behind the water pump housing) and the ECU sending ground the relays? I know I have read your thread on this maybe I need to re-read it.

DaleClark

iTrader: (55)

Fan switch is the Miata thermoswitch, that's all I'm talking about there.

The temp setting in the PowerFC is in Settings 3, Fan vs. Water Temp. There are 3 boxes there, Fan 1 AC, Fan 1 No AC, and Fan 2. Set them all the same. I would set them crazy low (like zero) to test it out.

If you bought a new engine harness, Mazda built some of the fan recall stuff into the new harness. If you have that AND the fan recall harness both plugged in it could do weird stuff.

If all else fails, see if you can track down an HKS Fan Controller, I don't think they're made any more and I'm probably the only FD guy that runs one. It gives full control over 2 fan inputs.

Also, if you ground the pin at the ECU side that should kick on the fans does it kick them on? I know you tested continuity, but that's worth testing.

Dale

davesan1

iTrader: (4)

On my 1993, per the ectrical manual, depending on operational mode, 2 of the 4 fan inputs can be connected to ground . One of them only connects to ground when relay # 3 is closed. The other should be permanently grounded via a solid connection to the body, (per the electrical manual). I think the fan permanent ground connection to the body in my car has broken. Can anybody tell me where this connection is located on the body? It is the yellow wire which goes to both fan connectors and disappears into a cable harness at the front passenger side. All the other wires from the fans go into this same cable harness and come out at the 4 fan control relays on the passenger side. However, this yellow ground connection line does not emerge from the harness at all, (so far as I can see), so it must be (inteneded to to be) grounded on the body somewhere between the fan connectors and the 4 relays, but I'm dashed if I can see where! If anyone knows, or has a stripped down car in their garage and can easily take an unobstructed look in that area I would be most grateful.

Thanks

Dave