temp sensor bad?

94Blue302GT · Aug 26, 2006

Ok, i've been diagnosing this problem for awhile, and i might have actually put something up a while ago, but this is where i'm at:
My car dies when it's warm, but when cold, idles beautifully.
255lb pump, bbk fpr, 39 lb injectors, 42lb forced maf, turbo.
It hasn't left the garage yet.
timing is dead nuts at 10' and the fpr will only let me go down to 40psi for some reason. I set it with vacuum off of it, and that's all the lower it would go. Doesn't matter, because with the mismatched injectors and maf, it likes to be at 42. I'm thinking that it's getting to the point where it gets warm and doesn't reduce the amount of fuel it's giving, and leaves the timing down, not allowing it to advance.
Is the only temperature gauge the one right behind the thermostat? Does this control the gauge and the engine temp or what? Is there a way to check the sensor itself, or should i just go and get a new one and see if that fixes it?
Any suggestions are welcome as the car is sitting in my parents garage and they want it out!!! I gotta get it back on the street!!!
Thanks!
Lee

HISSIN50 · Aug 26, 2006

Lee, you're right - the ECT is behind the t-stat (it has multiple wires). It's responsible for relaying coolant temps to the puter. You can ohm it out and interpolate the values to check calibration.

Good luck.

94Blue302GT · Aug 28, 2006

HISSIN50 said:
Lee, you're right - the ECT is behind the t-stat (it has multiple wires). It's responsible for relaying coolant temps to the puter. You can ohm it out and interpolate the values to check calibration.

Good luck.

Do u just check the ohms on the sensor or what? And what do you mean by "interpolate the values" I'm not familiar with that, sorry. I'd also like to check the wiring going to the sensor. I have well.... somewhat a unique setup, and i needed to extend the wires, is there a way to test that at all?
Also, since I have a turbo, some of the guys on the turbomustangs forums said i need to take the plunger on the smog connection and secure it halfway in at all times, since it is no longer active, otherwise i'll get codes, etc. Could that be at an incorrect setting?
OH, and also, my temp gauge and fan never turn on; i'm hoping all due to the sensor or wiring.

HISSIN50 · Aug 28, 2006

That's a good clue regarding the fan not coming on.

You're right - the ECT is a thermistor. When I check one, I ohm it out and either look at a chart or graph I have that relates what resistance correlates to what temperature. That's the interpolation (guestimating where on the chart the given resistance reading falls) part.

For you, the best way to test the resistance would be at the ECT input at the computer. That way, you'd see what the computer sees. Otherwise, if your splice on the way back to the puter is resistive, your reading at the sensor wont reflect that. I will note that IIRC, more resistance = colder motor.
If the ECT circuit was completely open (like one of your solder joints came apart), the low speed fan *should* come on at all times.

For the plunger idea, I think you're talking about the EGR. I have to keep the EGR functional here, so I havent hosed around with the plunger trick. A LOT of guys on here have though, and there might be something in the 94-95 FAQ Sticky at the top of the page about doing that.

Good luck.

94Blue302GT · Aug 31, 2006

So at what temperature does the computer start putting the timing and fuel back to normal? And what Ohm reading should that be?

Also, If i unplug the sensor, my fan "should" therefore come on constantly? That's strange seeing as that would mean it's like really really cold out. I think i'll unplug it and see if it turns on though.

Is there any other temperature sensor?
Also, does anyone know where on the computer the wires would be to check the resistance? I haven't really messed with the computer ever, just unspliced an alarm system, that was all.

68torinogt · Aug 31, 2006

why not replace it. its cheap

94Blue302GT · Aug 31, 2006

well, i replaced it with one off of my other stang, which is now in the junk yard, sniff sniff... but same thing happened, unless they were BOTH bad, which i doubt.

68torinogt · Aug 31, 2006

i get lots of bad parts but ill bet its not that then. when it dies does it sputter and then die or act like someone turned it off?

HISSIN50 · Aug 31, 2006

94Blue302GT said:
Also, If i unplug the sensor, my fan "should" therefore come on constantly? That's strange seeing as that would mean it's like really really cold out. I think i'll unplug it and see if it turns on though.

No, it would not mean that at all. The puter would realize that there's no signal return and realize it has no clue what the temps are (just as if the connector became undone while you were idling in traffic - that would not be a time when the motor is cold). The default is to have the fan run in such a situation.

94Blue302GT · Sep 4, 2006

Ok, the fan runs when unplugged. Dead cold, the ohms were at about 30. I also checked for resistance through the wires going to the computer, and I did get some, so it's not bad wiring, at least i'm assuming it's not. I did notice that my smog plunger had wiggled loose while messing with everything in the engine bay, so i'm rigging up a more permanent solution at the moment, consisting of leftover exhaust pipe and some jb weld, lol. Hopefully that is it then, i'll let you guys know by the weekend.

HISSIN50 · Sep 4, 2006

94Blue302GT said:
Ok, the fan runs when unplugged. Dead cold, the ohms were at about 30. I also checked for resistance through the wires going to the computer, and I did get some, so it's not bad wiring, at least i'm assuming it's not. I did notice that my smog plunger had wiggled loose while messing with everything in the engine bay, so i'm rigging up a more permanent solution at the moment, consisting of leftover exhaust pipe and some jb weld, lol. Hopefully that is it then, i'll let you guys know by the weekend.

If your ECT read 30 Ohms, you have issues. The ECT is a thermistor, the resistance of which goes down with temperature. If you saw 30,000 Ohms (30K of resistance in Ohms speak) and it was 75-80*F outside, then that's more like it.

Also, you don't want to see resistance in wiring to the computer. Shoot for seeing less than 5 ohms in generic puter wiring.

Good luck.

94Blue302GT · Sep 4, 2006

uhhhh..., yeah, actually, i just looked and my multimeter i have was on the x1000 setting, so 30,000 is about right. The resistance to the computer was small, but it still registered, so that's bad, right? Maybe it IS bad wiring.

HISSIN50 · Sep 4, 2006

94Blue302GT said:
uhhhh..., yeah, actually, i just looked and my multimeter i have was on the x1000 setting, so 30,000 is about right. The resistance to the computer was small, but it still registered, so that's bad, right? Maybe it IS bad wiring.

Cool regarding the ECT resistance.

When you checked the puter wiring resistance, if it was a handful of ohms you saw, you should be fine. Some less expensive (and even expensive) meters are not super accurate measuring tiny resistances, and if the battery in the meter is kinda dead, it can also read a little off (mine reads higher with a weak battery).

Good luck.

94Blue302GT · Sep 6, 2006

ok, i also redid the egr plunger deal.
Now it does idle much better. But only for awhile. I had it sitting there for 15 minutes, no change on the dash thermostat, and then it just flat out died again. It's like it cuts ignition, fuel injectors, everything, and just lets the fuel drain back down, that's it.

HISSIN50 · Sep 7, 2006

94Blue302GT said:
ok, i also redid the egr plunger deal.
Now it does idle much better. But only for awhile. I had it sitting there for 15 minutes, no change on the dash thermostat, and then it just flat out died again. It's like it cuts ignition, fuel injectors, everything, and just lets the fuel drain back down, that's it.

So you checked at you have no spark and no injector pulsing?

Do any of the sensor have voltage (put a test light on the positive side of an injector connector, and see if it shows 12 volts with the other leg of the test light grounded).

If you have no injector pulsing and no spark, it can be the PIP. If you also have no 12 volt signal to any of the injectors and sensors (including VREF), it could be the EEC relay inside the CCRM. Put your meter on the applicable CCRM pins (for the EEC relay) and see if they're hot.

If I thought about it, I could come up with a couple other possibilities, but there's no point without more detailed info.

Good luck.

94Blue302GT · Sep 7, 2006

Well, pip is new last year.
The car dies "as if" the ignition and fuel was cut. If i keep my foot in it, it keeps going. By that, i mean i can keep it above 1000 and it will continue to run, but anything under and it wants to just die. Also, I can start it again, but only if i put my foot in it a bit and/or repeatedly hit the gas.

94Blue302GT · Nov 24, 2006

I think it might be from old gas, would that do this? The gas is about a year and a half old, and I just threw in 5 gallons of new stuff, that bad?

HISSIN50 · Nov 24, 2006

94Blue302GT said:
I think it might be from old gas, would that do this? The gas is about a year and a half old, and I just threw in 5 gallons of new stuff, that bad?

I didnt re-read all this, so apologies if some of this does not apply:

If your car was not run much (being it that your gas is so old), partially clogged injectors can cause issues. Just getting some miles in them again (with clean gas and some decent injector cleaners if you desire) often helps. Or remove them and have them cleaned and flow-tested at a shop.

The gas is hit or miss IMHO. I've had old, untreated gas perform fine (some years back I let a 750CC bike sit for 3 years without starting. It's a kicker and started and ran great off the very first kick!) and other times I've had relatively fresh gas act like crap. I'd either drain the tank, or fill it up all the way so you dilute the old stuff. Burn through that tank and then you should be lookin pretty good. Adding some heat might not be a bad idea either.

Good luck.

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