How to: Re-wiring/providing power to ECT sensor

jaymac · Nov 11, 2005

So, I finally followed JRichker's advice and tried to test my ECT sensor for power/volts. Turns out there is not even power coming through the wires to the sensor.
So now, where do I start?
Is it possible to just jump pwer from another sensor to the ECT to power it up, or am I in for more of a PITA than that?
Any and all advice is appreciated.
Keep in mind, I am electrically retarded

Thanks,
jeremy

jrichker · Nov 11, 2005

The ACT sensor only has 2 wires, a signal ground (black/white) and signal (dark green/lt green). There is no power wire.
Diagram courtsey of Tmoss & Stang&2birds...

jaymac · Nov 12, 2005

It's actually the ECT sensor, but same story I guess. I'm going to probe the 10 pin today and see if it's dead there. If it's dead all the way to the computer, then what??

jaymac · Nov 14, 2005

well, upon further test-light testing, the ACT snsor has no signal either.
Then I disconnected the salt and peppers also and tried to test those leads and didn't find any signal (no light on the test light) on any prong except the EVP, which has been throwing a code since the day I got the car.
Go figure.
Then, by the computer, I found a Green/yellow wire in a connector, and it lit up the test light, Is there only 1 g/y wire, or could this be something else?
Where do I look next?
What could this be affecting, if I have no signal to my ACT/ECT, and how do I fix it!?!?!?

jrichker · Nov 14, 2005

jaymac said:
well, upon further test-light testing, the ACT snsor has no signal either.
Then I disconnected the salt and peppers also and tried to test those leads and didn't find any signal (no light on the test light) on any prong except the EVP, which has been throwing a code since the day I got the car.
Go figure.
Then, by the computer, I found a Green/yellow wire in a connector, and it lit up the test light, Is there only 1 g/y wire, or could this be something else?
Where do I look next?
What could this be affecting, if I have no signal to my ACT/ECT, and how do I fix it!?!?!?

There is a light green/yellow wire (ECT) and a dark green/yellow wire ( IDM)

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-90 wiring

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

jaymac · Nov 14, 2005

so is there a possiblity saomehting inside the computer itself is blown/faulty, or does this sound like strictly an external wiring thing?
And lastly, what kind of symptoms/conditions could this be causing?

jrichker · Nov 14, 2005

Bad ECT causes hard starting , high fuel consumption, poor performance.

I would disconnect the computer wiring plug at the computer and measure the resistance from the ECT pin 7 to the ECT sensor connector on the engine. You should see less than 1 ohm. Do the same for the ACT pin 25 and the ACT sensor connector on the engine. Again, you should see less than 1 ohm.

jaymac · Nov 14, 2005

don't you love all my questions?

And if I don't see less than 1 ohm?
If it's bad, would I see NO ohms, or more than 1?
I would assume the car's battery would have to be connected to test this? It appeared to me that I had to remove the computer ground strap to pull the computer from the kick panel, and I thought doing that would ground out the computer.
So what should I do? Disconnect the battery, then the ground strap, remove the computer, re-connect the ground strap, then reconnect the battery, then re-test?

Again, thanks for the help

jrichker · Nov 14, 2005

Anything 1 ohm or less is good. More than 1 ohm but less than 100 ohms means some dirty connections. More than 100 ohms is a wiring problem that needs further investigation.

Simply disconnect the computer wiring connector from the computer. You don't have to do anything with the battery or grounds. The secondary ground (ground for the computer case) should be long enough to give enough slack to move the computer connector.

If you need help with basic automotive electrical troubleshooting, this is the place to start. See http://www.autozone.com/servlet/UiB..._us/0900823d/80/1d/d8/76/0900823d801dd876.jsp and carefully study ALL the information under the Heading Chassis Electrical, Basic Electricity – Understanding & Troubleshooting.

jaymac · Nov 16, 2005

OK Jrichker, or anone else who knows/cares, I checked the ohms between pins 7 and 25 and their sensors, and got .3-.4 for both.
So far so good.
Then I checked continuity between both and it beeped.
Also good.
Then I checked the voltage for each sensor connector, KOEO, and got roughly 4.5 for the ACT and the ECT.
Is this correct? If not, where I go next?
Thanks again

jrichker · Nov 16, 2005

Reconnect everything and get the engine running. Then use some safety pins to probe the ACT & ECT from the back of the connector. Use the black lead of the DVM on the black/white wire and the red lead of the DVM on the other wire.

If the outside air temp is below 50 degrees F, the ACT may not read correctly.

Make sure the engine is up to operating temp prior to measuring the ECT. If the coolant temp is below 50 degrees F, the ECT may not read correctly.

You should see some voltages compatible with this table:

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

The above values are +/-20%

jaymac · Nov 16, 2005

OK, so get the enigine up to temp., then SHUT IT OFF(?) to do the test??
Right now, I tried probing from the back, and got absolutely NO readings? So get it up to temp, kill it, and then measure, or measure while it's running?

jaymac · Nov 16, 2005

OK, I was able to pull volts once the engine was up to temp. It was .9 @ 180ish on my Sunpro, which could be give or take a few degrees.

SO, If my ohms check out, my volts @ the connector(unplugged) read 4.6 KOEO, and my volts, sensor plugged in, read .9, why am I getting a code for the ECT? I did recently replace it, could it just be bad?

jaymac · Nov 17, 2005

somebody needs to make a smilie for "bump".

Oh yeah, and "bump".

jrichker · Nov 17, 2005

jaymac said:
OK, I was able to pull volts once the engine was up to temp. It was .9 @ 180ish on my Sunpro, which could be give or take a few degrees.

SO, If my ohms check out, my volts @ the connector(unplugged) read 4.6 KOEO, and my volts, sensor plugged in, read .9, why am I getting a code for the ECT? I did recently replace it, could it just be bad?

Warm the engine up & unplug the wiring connector from the sensor. Carefully open up the radiator cap. Use a cooking thermometer to measure the coolant temp. Then check the sensor resistance against the following table:

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

J90GT · Nov 17, 2005

hmmm seems like alot of work. Why dont you just find a new/good used fuel injector harness?

jaymac · Nov 17, 2005

so am I measuring using the prongs on the sensor itself, or on the plug?

jrichker · Nov 17, 2005

jaymac said:
so am I measuring using the prongs on the sensor itself, or on the plug?

The sensor itself. The resistance values should be the same as the chart +/- 20%

The other approach is more work, but may prove to be more useful, since it includes the wiring resistance. Just make sure you know how to read your meter, since some of them autorange and it can be misleading if you don't pay close attention.

Make sure the sensor is connected to the wiring harness. With the engine warm, disconnect the computer connector. Measure the resistance between pins 7 & 46. The resistance values should be the same as the chart +/- 20%

Either method is good, the last method is the best.

95cobradude · Nov 17, 2005

before u go through any of that u can have somebody hook up a scan tool to the car and see if u get a coolant temp reading on the scanner. if there is a reading then the computer and the sensor is doing its job.

jrichker · Nov 17, 2005

95cobradude said:
before u go through any of that u can have somebody hook up a scan tool to the car and see if u get a coolant temp reading on the scanner. if there is a reading then the computer and the sensor is doing its job.

Unfortunately, the output from the computer is rather primitive and you don't get info like that from an OBDI computer. If you have a Tweecer or Anderson PMS, you might be able to get that information.

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