New temp gauge & code 21: coolant temp out of range

jaymac · Aug 3, 2005

I installed the new temp gauge and it's reading right @ 180*, but I ran the codes cuz it idled a little rough today, and it pulled code 21, which is coolant temp out of range.
Is this because I disconnected the factory wire that the ECU reads?
Will the computer pull/change timing or anything else that will negatively affect performance since it's not reading coolant temp?
Could I/should I connect the factory wire on top of the sender in addition to the new gauge so the ECU doesn't do anything funky??
Thanks,
Jeremy

jrichker · Aug 3, 2005

The ECT sensor lives in the tubing for the heater on the passenger side of the engine.

The engine coolant sender for the temp gauge is in the front of the driver's side of the lower itake manifold. The temp sender for the gauge has nothing to do with the ECT sensor.

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor. Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the RH front of the engine in the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from the rear. Use care in doing it so that you don't damage the wiring or connector.

Here's the 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

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

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

A faulty ECT sensor can cause hard starting when hot and poor fuel economy.

jaymac · Aug 3, 2005

jrichker said:
A faulty ECT sensor can cause hard starting when hot and poor fuel economy.

First of all, thank you. I'm very impressed by your wealth of knowledge!
Secondly, I think that's exactly what it is, since I used to get 20 mpg before the head and intake swap, and since the swap it's dropped to around 12.5, even w/ slow driving. That's HUGE.
Also, if I'm driving around for a few minutes, then try to start the car again, it will either bog HARD, and lope for about 30 sec., then even out, or sometimes just die, then I'll start it again and it will run. Sometimes even after an hour, it will still have a lopey idle.
I thought it might've been the TFI, but I just replaced that awhile ago.
Everything you described so far sounds like the ECT sensor might be bad..

How do I go about replacing the ECT sensor if it's in the water tube?
(do you mean IN the tube or "screwed" into the tube).
All your electrical info is fantastic, but a little beyond my current scope - probably be good to learn, though!
Thanks again!

jaymac · Aug 3, 2005

OK, sometimes I can be self-sufficient

I went and found the ECT and am just going to replace it and see if it helps.
It's $15.99 @ Autozone, so it's worth a shot, right?
1.) Will I need to drain any coolant,
and
2.) Will I need teflon tape, liquid thread sealer?

Thanks again!!!!!!!!!!!!
(what would I do w/o Stangnet, and what would Stangnet do w/o Jrichker???)

jrichker · Aug 3, 2005

jaymac said:
OK, sometimes I can be self-sufficient

I went and found the ECT and am just going to replace it and see if it helps.
It's $15.99 @ Autozone, so it's worth a shot, right?
1.) Will I need to drain any coolant,
and
2.) Will I need teflon tape, liquid thread sealer?

Thanks again!!!!!!!!!!!!
(what would I do w/o Stangnet, and what would Stangnet do w/o Jrichker???)

There will be some coolant spillage when you remove the ECT sensor. If you are fast at removing the old one and putting the new one in place, you may not have to worry about draining the radiator. I would try and get away with not draining the coolant. Just be sure that the new ECT sensor is already prepped with whatever thread sealant you are going to use.

I use blue silicone on the new ECT sender threads to seal it. Some Teflon pipe dope or Teflon tape would work just as good. Just try to keep the big messy gobs of silicone or pipe dope off the sensor element.

jaymac · Aug 3, 2005

jrichker said:
If you are fast at removing the old one and putting the new one in place, you may not have to worry about draining the radiator.

That's what I did yesterday when I replaced the sending unit for the temp gauge. Pulled it and popped it in quick, had towels all around the intake.

Question:
Do YOU ever need help w/ anything, or ask questions of anyone, or are you just here for all of our salvation?

HISSIN50 · Aug 3, 2005

jaymac said:
Question:
Do YOU ever need help w/ anything, or ask questions of anyone, or are you just here for all of our salvation?

He is a huckuva guy - the only time he seems to post new threads is to share information with us. Seems to me the last thread he started was that wonderful 'Surging Idle' sticky at the top of the sub-forum.

When one (JR) knows everything, there is no need to post threads asking questions.

jaymac · Aug 3, 2005

yeah, JR's gonna be the end of this business.
He should have his own website, write his own book, etc.
Anyhoo, I swapped in the new sensor and started her up- code disappeared right away, no surging idle at start-up, then I killed it and started it up right away, which would before, surge and die, and no surge, no die
Now, as far as my mileage, owuld that bad sensor have been fouling plugs all this time, or is there anything I should check as a result of this being F'ed up all this time?
Lastly (and a shot in the dark), would the bad sensor affect 1/4 performance at all, cuz I had all the symptoms for my last run, too)?
Next time I'm in your area, (Hissin' and JR), I gotta take you guys out for a beer!!

HISSIN50 · Aug 3, 2005

Joe will have much better info than I will. But I do think that a bad ECT would affect drivability across the board, since the amount of fuel trim is partially dependant upon its input.
Exempli Gratia: it was telling the puter that the car was hot, when in fact it was stone cold, you would be very lean. And I think this condition would continue in most aspects of driving.

You could pull a plug, but I kinda doubt you would need to do anything. EFI still (even when in poor tune, like having a bad sensor) is pretty lean and clean. Carb'd motors had more washdown and carbon depositing.

Let's see what the master says.

jaymac · Aug 3, 2005

I have yet to drive it after the swap, just let it idle for a few, so we'll see how it feels tomorrow. I REALLY hope my fuel economy comes back, cuz goin' from 20 mpg to 12.5 mpg @ $2.57/gal. is NOT cool...
By the way, you, sir, are the "Post Master"

HISSIN50 · Aug 3, 2005

jaymac said:
By the way, you, sir, are the "Post Master"

I just find myself coming back here time and time again. And I am JT, not sir. Elders to me are Sir, but not I.

jaymac · Aug 3, 2005

Well, "JT", according to Stangnet, you come back here 15.11 times per day for the past 2 years!!
that's dedication - you earned the "Officially addicted" title.
I wonder what the next title up is??

The Shape · Aug 3, 2005

Wait a minute then . How come you said I had to call you sir and send you 20 bucks everytime you anwsered a question for me then JT???

HISSIN50 · Aug 4, 2005

The Shape said:
Wait a minute then . How come you said I had to call you sir and send you 20 bucks everytime you anwsered a question for me then JT???

Here is the caveat - you don't need answers from stupid me; you are smarter than I. And if you did send money, my advice is worth about 2 cents, not 20 bucks.

So, i bug people on here 15 times a day.Hmmmm. I feel bad for those folks.

jaymac · Aug 4, 2005

jaymac · Aug 4, 2005

bump for "other replacement items from subsequent damage" question

jaymac · Oct 11, 2005

OK, so however long after the first replacement, I pulled the codes again while changing the oil, and got code 21 again. COuld this just be a crappy sensor I replaced it with? Or should I look somewhere else? If so, where?

jrichker · Oct 11, 2005

Go back to my orginal post and get out your voltmeter/ohmmeter. Use the information I posted to check the sensor. If the sensor passes the voltage and resistance checks, you have a wiring problem.

The Shape · Oct 11, 2005

Did you disconnect the battery after replacing the sensor? That will clear the computer and get rid of the code.

jrichker · Oct 11, 2005

The Shape said:
Did you disconnect the battery after replacing the sensor? That will clear the computer and get rid of the code.

Good point, but the codes will clear automatically after 87 startup cycles. Why 87 and not 90? I have no clue...

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