F1blueRx7

iTrader: (5)

I need to test the wiring to/from the ECU to verify that there is not a short in the two wires that run to the sensor.

Assuming the water is cold what should the voltage be at the switch? and should it be the same at the ECU pin outs.

I'm trying to save myself from buying a water thermo switch if the problem is with the wiring harness.

HAILERS

Well. It's 2.34 on one car that hasn't been run since 2am this moring and it's 2.7 vdc on another car that hasn't been run since day before yesterday. And it's 7:30 am now.

The outside air temp OAT is 51.4 F.

So just see what yours is when the thing is cold then leave the meter on the pin and warm the car up. Once fully warm/hot the thing should read .5vdc give or take depending on the thermostat in the car etc.

The voltage should steadily drop from the two something volts down to that half volt give or take figure.

I'm talking WATER THERMO SENSOR. Green plug on the back of the water pump housing.

F1blueRx7

iTrader: (5)

Thanks hailers I'll test it this evening after my car cools back to ambient temps. (ranging from 20-70 degrees in baltimore... whacky weather).

F1blueRx7

iTrader: (5)

I put a new thermo sensor in, seems to be fine, 14 bucks from the parts store. It's been 70 Degrees the past few days so I'm going to have to wait for a really cold day to be sure, but it seems fine.

F1blueRx7

iTrader: (5)

hailers I'm seeing 4.8v at the water thermo sensor with the car cold. I re-grounded a few things and thats when the problem started. I only added one ground, at the boost pressure sensor. and cleaned up the harness grounds:

1. At the firewall to trans tunnel (Replaced wire with 10 gauge wire and solder on ring terminal connectors)
2. Next to the trailing coil (wire brushed, added dielectric grease)
3. Bottom of the drivers side strut tower (wire brushed, added dielectric grease)
4. I have one ground running from the battery, to the rear Iron and have the ECU harness ground run there.

I'm at a loss somewhat. I'm assuming I moved the harness in a way that broke a wire and now those two are shorting out against each other.

Any ideas?

HAILERS

What you do is this: You leave everything connected to where they go.

You go to the ECU and backprobe the green/white wire in the middle ECU plug with the connectors all ON. Pin 2I on a series four car.

You turn the key to ON only.

Read the voltage on that pin 2I , the green/white wire. On a very cold day it might read as high as 3 vdc.

Now start the car and let it warm up while WATCHING the meter. The value will steadily drop down til it reads approx .5vdc (half volt dc) when the engine is fully hot.

IF it does that, then there's nothing wrong.

F1blueRx7

iTrader: (5)

On a series 5 it's a green/yellow wire at 2E. It's reading 4.8v cold or warm, and according to the Wiring diagrams it should start at 2.5-2.8 and drop to .5.

So I'm going through the harness now looking for some bad connection.

F1blueRx7

iTrader: (5)

Hailers, for testing purposes is it possible to splice a wire at the thermosensor and run it straight back to the ECU and splice it in at 2E to verify if there is a problem with the wire? Looking at the Wiring diagram it appears to be a straight run back to the ECU. This look kosher?

arghx

iTrader: (3)

can you really get a thermosensor for like 15 bucks? if so, just change the thing. No sense in spending hours diagnosing it... if it doesn't break now, it will later.

EDIT: http://www.mazdatrix.com/getprice.as...m=18-8400-8574

$28.14 + S&H from Mazdatrix, and probably cheaper than that if a local store carries one.

HAILERS

Well you could run a wire.

But what I'd do is pull the plug off the ECU and put one meter lead on pin 2E in the plug and then run the other lead of the meter to the plug in the engine bay and put it on the green/white wire of the plug that connects to the sensor. It should read continuity.

IF it does not then run a new wire. If it does read continuity then the problem is not that wire but either the connector or the other wire (brown/black) is busted. The brown/black is spliced to a number of other sensor gnd wires and finally makes it's way back to the ECU pin (well I forgot the ECU pin. It's shown on that page your showing).

If you meter leads are not long enough, then put a long piece of wire on one of the leads and make that wires other end you probe in the engine bay.

Water thermo sensors do not go bad unless you bust the dang connector/jack to shreads.

I don't see how that wire could have gotten broken. The green/white wire. No connectors inbetween.

I mean to check that sensor all one has to do is put one meter lead on a good ground in the car and the other lead up the back of the green/whtie wire. Meter on dc volts and key to On and it should read 2-3vdc and then if you start the engine the voltage goes down until it reaches a half volt or so. You never have to take a elect plug off, just make sure they're connected.

F1blueRx7

iTrader: (5)

I've already replaced it.

F1blueRx7

iTrader: (5)

I'm telling you man, I've checked this damn sensor 6 million times. It's at 4.89 volts no matter what temp the car is at. Hot or cold. I've tried regrounding the sensor harness on the top of the block and running a new ground from there right back to the ECU ground in the cabin. I'm considering running a ground right off the thermosensor wire to the top of the engine block.

I'll check your idea for continuity, but I think it's shorting out against some other wire in the harness, hence the higher voltage.

HAILERS

I don't think its shorting out. I think there is an open wire, either on the green/white OR the brown/black wire. IF the green/white was shorted the voltage would drop to zero/zip.

I'm misunderstanding something. Just where are you reading the 4.5volts???? At the sensor plug or at the ECU?

F1blueRx7

iTrader: (5)

At the ECU Pinout 2E and out of the Green/White Wire at the plug which runs back to 2E on the ECU.

RotaryEvolution

iTrader: (30)

from the schematice i would think an open would read 0 volts at the ECU not 5 volts, a short would read 5 volts. the BR/B wire is the 5 volt reference wire(at least the way it appears, half of the schematic is cut off so i can't be sure), the opposites into the ECU are the signal wires(after the resistance through each sensor the signal is modified and sent to the ECU).

however i have seen the pins push back in the connectors quite a bit on these cars, that is something to check for, pull the connector off the back of the thermosensor and look at the pins, if one looks like it is pushed in then BINGO!, there's your problem.

F1blueRx7

iTrader: (5)

BR/b is a ground wire. It runs to ground according to the Wiring manual.

here is the full manual


http://www.irixbox.com/rx7/s5wiring.pdf

RotaryEvolution

iTrader: (30)

then you have an open circuit, try what i suggested in my last post and i bet you find a pushed in pin or broken wire near the sensor.