I will rerun the ECT resistance and voltage with KOEO as you have asked tonight. THe needle on the dash is acting the same with the new thermostat as it did with the old one. SO im guessing it is not faulty, especially since the old one tested to be okay with boiling water test. I did measure the engine while running after it had been driven for ~ 25 mins.

DO you think that the over cooling could be due to faulty fan clutch? I know these things are thermo sensitive, forgot the word but maybe its engaged all the time? Would that explain the overly cooled engine?

 

OK, now lets not confuse the ECT sensor, which is the multi-wire one, that the computer uses to sense engine temp & the separate single wire temp sensor thats used Only for the instrument panel temp gauge.

The Computer is unhappy about the reading it's ECT is sending, it's not connected to the temp gauge sender for the instrument panel.
If you want to check the temp gauge, you could disconnect it & ground the lead through say a 5K ohm resistor & se if it'll read up scale. If you don't mind slamming the meter movement, you could just directly ground the lead & see if it'll go full scale.

If we're driving on the highway, or above about 30 mph, we really don't need a fan, as unrestricted air flow through the radiator is usually enough for the radiator & a properly working thermostat to keep engine temp within bounds.

So for the engine to really be overcooled in summer, you most likely have a sticking open thermostat, or a wrong temp range thermostat installed, imo.

Your heated thermostat "open" test really didn't check it's ability to close properly, so if it opens at the right temp, but hangs open, it'll overcool & most thermostats are designed to fail in the open mode, so the engine won't over heat, so keep all that in mind.

More things to ponder.

Hang in there & keep us posted, I believe your about to tumble to a conclusion!!!!

 

Okay if i did this right

i got 4.75 volts from ect side KOEO at 113 degrees F
Resistance on signal return to ground was 105

I know you asked these at room temp so i will try to let the truck cool off more and retest but this is what i have so far. Not sure what it means so help me out please.

 

Another test this time radiator fluid at 96 degrees Fahrenheit.

REsistance between the 2 pins on the ect = 17.4
Voltage with KOEO at 96 Fahrenheit 4.74

The resistance seem to be close to the spreadsheet someone posted but the voltage reading seems to be off. Can someone confirm this and if this is the case does that mean i need a new ect? This one is only a few months old.

 

Was the ECT resistance reading of 17.4, with the ohmmeter set to the X1000 ohms scale, or was it set to the X1 scale?????

 

okay not sure on the scale ill have to check the meter when i get home. I had to borrow this one b/c the one i usually use is the little cheapy needle one and this is a huge yellow monster.

In addition b4 i took off for work this morning the radiator fluid had cooled to 86 degrees.

I retested and got 4.7 voltz
25 resistance using the ohms function.

I have not changed the ohms scale on any of these readings so far so whatever the scale has been it has not changed with any of these readings.

If im reading this chart right my resistance seems to be okay but the voltage is off, is that from computer malfunction or ECT problem?

 

Well lets see, if you look at the top of the reference chart resistance colum, you'll notice the scale is in K Ohms (thosands of ohms).

So the difference between reading 25 ohms on the X1 scale & reading 25 ohms & being on the X1000 scale is a HUGE (1000 times) difference, to the computer!!!! ie the difference between 25 & 25,000 ohms, so we need to know what scale you made the resistance readings on!!!! X1, X10, X100, X1000!!!???? The meter likely has all those multiplier scales to choose from, so you refer to the ohms scale on the meter & read the number, then multiply it by the multiplier scale chosen.

I wouldn't worry about the 5 volt reference measuring 4.7 volts, thats only 300 milvolts & the meter may not be that accurate. IMO the reference voltage is likely ok.

My guess is that IF the error code 51 you posted is a valid one, either the sensors resistance, or the signal return wire to the computer is faulty, as the code given (51) says the computer thinks the engine is at a freezing cold -40 deg. or that the signal return wire to the computers under hood electrial connector is open circuit, some where between the ECT to the computers electrical connector.

So once we know for sure what resistance multiplier scale you were using & thus the real resistance value you posted, we'll know the state of the ECT sensor & can decide if it's the culprit, or if the signal return wire is likely open circuit. WHEW!!!!! lol

 

IM guessing it was in K ohms b/c i talked to the electrician who let me borrow his meter and he said it adjust to whatever it needs. (its in auto mode) I will double check that when i get home to make sure. I hope its the sensor even though its new b/c tracing that wire back to the computer could be painful.

 

I double checked the resistance and it was measuring them in K ohms.

 

Ok good feedback, so now we know for sure that the ECT resistance you measured is within spec at 86 deg F.

It's spec at that temp, according to the ECT chart in the link I posted is 24.27K ohms +/- 15% & you measured 25K at 86F which is good.

Now the ECT reference chart says that at KOEO, the signal return voltage going to the computer, at 86F, with the ECT's electrical connector fastened & assuming a 5 volt reference, should be 2.62 VDC +/- 15%.

So without a breakout box, you'll have to probe the signal return wire at the computers firewall electrical connector, to see if that signal return voltage is reaching the connector, which would indicate the lead is good. Or disconnect the ECT & computer connectors & do a end to end resistance check on the signal return wire.

If you find that the signal return voltage is low with everything hooked up, probe the 5 vdc ref voltage lead, to make sure it's ref voltage isn't dropping under load. If it is, suspect a corroded or loose connection somewhere between the computers firewall electrical connector & the ECT's electrical connector.

Let us know what you find.

 

im guessing you are referring to the computer down by the passenger side kickpanel? IF so there are like guessing 60 wires or so. How do i know which wire to probe?

walk through or a little more detailed help would be greatly appreciated.


thx.

 

Well I don't have a reference manual for your year/model, so I suppose you'll have to come by one.

Maybe you can find one at your local library, or autoparts store.
Or maybe a member reading this can provide you with it's location on the computers input connector.

Then check the return wires color code at the ECT & probe it with a pin to see what the return voltage is, coming out of the ECT sensor, it should be close to the values listed in my above link, for the temp the ECT sensor is at test time, then find that color code wire at the computers connector & probe it & see if the return voltage is making it to the computer.

 

I back probed the ect return wire at the computer and it was reading .15 volts. I back probed it at the ect and it was .167 volts. Is that close enough? It was a gray wire with a red stripe.

There are 2 ground wires on the body near the computer (behind kick panel) some appear to have small amounts of corrosion and a green film, I will clean these but could that be part of my problem? Just another thought.

 

How do you perform the end to end resistance check on the signal return wire?

thx

 

This is gonna get kinda long & wordy.

Assuming a 5 volt reference & a temp of 86F, the return voltage to the computer should be on the order of 2.62 vdc +/- 15%, so the signal return voltage at the ECT sensor, all the way to the computer is very low & WAY below where it should be.

The drop in voltage on the signal return wire, between where you probed it at the ECT & on the computer end, is probably reasonable & kinda sounds like the signal return lead may be ok, but I'd measure it's end to end resistance anyway.

So the problem it seems, is either with the ECT sensor itself, or maybe with the 5 volt reference, with it connected to & under the ECT's load.

So at KOEO, with the ECT's electrical connector in place, probe the 5 volt reference wire & see what it's reading while connected to the ECT.

If it's low when under load, suspect a wiring problem with the 5 volt reference wire. Maybe corrosion on the ECT end, maybe on the computer end. Could even be broken wire strands, or corrosion of the wire strands under the insulation, where the wire strands are crimped to their connector pins or sockets, on either end.

So, if the ref voltage is low at the ECT end, also probe the ref voltage wire at the computer end at KOEO.

If the ref voltage is low at the computer end, suspect a problem with the wires connection at the computer connector, or a problem inside the computer.

If the ref voltage is ok on the computer end, but low on the ECT end, suspect a wiring or pin/socket problem between the computer connector & the ECT connector.

For a resistance check, you could rig a long test lead that would reach fom the ECT connector to your ohmmeter.
Then touch the long ohmeters test leads together, to zero it on the ohms scale your going to measure the wires resistance on, so the meter is zeroing out the test leads resistance. Then make an end to end resistance check of the suspect wire.

You could also check the body to engine resistance, then if any, zero the ohm meter to take out any measured body to engine resistance, then with the ignition OFF, ground out the ECT signal returns lead to the engine & measure the signal return leads resistance to ground, on the computer end.
Having pre-measured & zeroed out any engine to body resistance on the meter, it should yeld a fairly good measure of the signal return wires resistance.
WHEW!!!! lol
Let us know what you find.