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Thread: Best part number/item for thermostat gasket?

  1. #16
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    Strictly via the PCM as i understand it. I don't recall any direct connection between the ECT and IRCM, otherwise.

    AFAIK, the PCM sends out the ref. voltage which the ECT uses to send a signal that varies based on coolant temp, back to the PCM, which then (among other things based on engine temp) executes strategy/triggers the IRCM, which then lights the fan, based on.

  2. #17
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    Well if that's the case then the ECT is a crucial part of the system. I did find my problem. I must have bent a pin probing it with my VOM several months ago when i was looking at my supposed PCM issue. I didn't have 5V and my continuity was fine between that connector block and the sensor itself. I bent the pin closed slightly and got the circuit working. Funny thing - the check engine light was still on. I let it warm up in the driveway and then took it for a short drive. For some unknown reason I paused, shut down the car and it would not start back up - exact same symptoms I've been fighting all summer. Left the car and walked home (not far). Went back just now and it fired right up. CEL code cleared too. Odd as heck if you ask me.

    At this rate I've worked on it more than I've driven it. I'm really considering listing it for sale. I'm done tinkering - I'd like something fun to drive that requires less maintenance. The "cool" appeal of keeping this car on the road has lots its luster.

    Thanks for the help again Ken

    Anyone near Denver want a rust free 94 SC Auto?

  3. #18
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    Quote Originally Posted by potshotscott View Post
    ...must have bent a pin probing it with my VOM several months ago when i was looking at my supposed PCM issue.
    Feel your pain. I had a fresh one that sunk a pin when the connector was in place. It would barely make contact...sometimes - it was new so i kept looking elsewhere. These days, if there is any question surrounding the ECT I just warranty it for a new one and move on. I've got a 1/2 dozen old ones pulled from wrecks and none of them bench test the same.

    Interesting discussion here, I think: https://www.underhoodservice.com/dia...ature-sensors/
    Last edited by KMT; 09-14-2019 at 11:29 PM.

  4. #19
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    Sorry to dig this old thread up but my problem persists. Ken, you've been very helpful with this. Here's my problem - quite frankly these wiring diagrams are too simple. Meaning they're not descriptive enough. Aircraft manuals in the Navy go into full detail on what is expected on each pin of a connector. In the example attached all that is mentioned is Signal Return (PCM Pin 46) and ECT Signal (PCM Pin 7). I have the EVTM and can chase all of that no problem. I guess the crazy question I have is this; Is the signal return the 5VDC line while the ECT Signal is the thermistor adjusted Voltage heading back to the PCM? I have to believe it is. Although what's odd is that with the connector disconnected from the sensor I read about 5V on EACH PIN. That quite simply can't be correct in my mind unless I'm crazy. Starting to think I have another issue but I have to wait until the weekend to dig in.

    Again - sorry to beat this thread up again but does anyone have an accurate account for what Ford means when they use the term "Signal Return"? In the EVTM it's common to a BUNCH of sensors - I highly doubt its anything other than a 5V feed into each sensor.

    Thanks in advance.94SC Schematic_Block Diagram.pdf

  5. #20
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    Quote Originally Posted by potshotscott View Post
    In the example attached all that is mentioned is Signal Return (PCM Pin 46) and ECT Signal (PCM Pin 7). I have the EVTM and can chase all of that no problem. I guess the crazy question I have is this; Is the signal return the 5VDC line while the ECT Signal is the thermistor adjusted Voltage heading back to the PCM? I have to believe it is. Although what's odd is that with the connector disconnected from the sensor I read about 5V on EACH PIN. That quite simply can't be correct in my mind unless I'm crazy. Starting to think I have another issue but I have to wait until the weekend to dig in.

    Again - sorry to beat this thread up again but does anyone have an accurate account for what Ford means when they use the term "Signal Return"? In the EVTM it's common to a BUNCH of sensors - I highly doubt its anything other than a 5V feed into each sensor.
    Correct, simply a low voltage baseline. That's the 5v DC ref. out of the PCM/EEC and the input to several sensors.

    Just to be sure we're on the same page, the 'signal'* is the output from the sensor, fed into the PCM/EEC. DO NOT ATTEMPT TO READ ref. voltages with the related connector(s) unplugged from their sensors. They -must- be read with the system live, connected and with sensor loads in place Trying to check reference voltage by unplugging the connector is a no-go.

    Always backprobe, then check key on. DVOM recommended so you know it's value and not just that it's hot. This can be critical so you don't get fooled into relying on an out-of-spec reference voltage.

    I read the output off the ECT via backprobing as well. After confirming 5v ref. in (might be as low as 4.5v actual), you would expect to see a voltage drop coming out from 3.51v at 50, to 0.46 at 212

    LG/Y is signal out at ECT. This goes to the EEC. Backprobe it to check when engine runs and heats up. Ground black lead off meter to complete circuit to test. If meter does not auto range, be sure to use lower scale to read DC 5v and less. Have to admit I've never paid much attention to ref. voltage in the past. Been trying to adopt better elect. troubleshooting skills, including using a an o'scope for testing. The more you learn about sophisticated auto circuitry, the better chance you have of keeping cars like the SC going, I guess. A test light will get you only so far these days.

    About your diagram... 46 should be the 5v ref. (again, used by several circuits) ...beyond me why that diagram calls it SIG RTN (return), tho. I'm calling radishes on that...

    7 is the (adjusted) output from the sensor/thermistor. What are 46 & 7 named in the PCM's/EEC's connector face/pinout in the EVTM?

    *Note my habit is to refer to sensor output as a 'signal' (variable), and ref. voltage as a 'feed' (constant), but that's just me, so don't be confused. The factory diagrams call 7 'feed', opposite my habit. No matter, we both agree/consider 7 as the ECT's adjusted output that the EEC uses (among other inputs) to decide fuel strategy.

    Sorry if I'm repeating myself here.

    Ken
    Last edited by KMT; 01-07-2020 at 02:07 AM.

  6. #21
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    Thanks for confirming my thoughts. This will make the troubleshooting effort make 100% sense now. From here it's divide and conquer - should be simple. "Should" except its likely something broken or melted buried under tubing and harnesses.

  7. #22
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    For this kind of troubleshooting I find the EVTM's to be frustrating. They try to tell you what you need to know but they don't tell you what you will actually find in the vehicle. I find I use the actual vehicle wiring diagrams 99% of the time. They tell you exactly how many connectors there are in the system, what they look like, and where they go. Well, electrically where they go. Physically you still have to find them. But to me the big thing is they tell you exactly what else might be connected into a particular circuit and what definitely isn't.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  8. #23
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    Dave - which actual diagrams are you referring to? Is there something better than the EVTM? I've got tons of books for this car...

  9. #24
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    Believe that Dave is refering to these wiring diagram available in the SCCoA blog. Here is a link to the 1992 SC / Thundebird one.

    http://www.sccoa.com/WiringDiagrams/...%20Diagram.pdf
    '90 SC 5 Spd, Oxford White/Black Leather, 1 owner -- XB-70 - AV1
    '92 SC Auto, Oxford White/Black Leather, -- "Weed" - aka XB-70 - AV2
    '90 SC Auto, 35th, all options car, -- "Phenix Bird"
    '95 SC 5 Spd, OP White/Grey Leather, -- DLF's built SC -- "Mr. Hyde"

  10. #25
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    OH SNAP! I forgot I had one of these up on my shelf in the garage! Thanks for the reminder guys!

  11. #26
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    Well I FINALLY got this solved. Nice day here in Denver today so I rolled the old girl out into the driveway and tool the PCM out so I could do some Ohming out. Found a bad pin in the main harness at the back of the firewall going into the PCM. I had 4 K Ohms from the sensor return to the PCM unless I wiggled the harness a bit. Thought it was a bad wire but the contact is a little sloppy. I pinched it together a bit and the code cleared. Drove it for 15 minutes and it came back. Planning to get some Arctic Silver conductive paste to put in the contact unless someone else has a better idea. I have no idea what pin extraction tool would be needed to pull the pin to make it tighter. If anyone does know what tool I could use besides a small screwdriver I'd love to hear.

  12. #27
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    Remind me, are you working with pins/male on the connector side, and contacts/barrels/female on the ECU side, or?

    Arctic Silver conductive paste
    About Arctic Silver...it is 'thermally' conductive.

    "Arctic Silver 5 was formulated to conduct heat, not electricity. ... While it is not electrically conductive, the compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths".
    Last edited by KMT; 03-15-2020 at 12:30 AM.

  13. #28
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    I am working on the female side of the harness that goes to the ECT. I was hoping since the compound has silver in it that it was conductive. I guess I'm gonna have to find something else.

  14. #29
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    De-pinning tools are low cost and many to choose from via eBay, but the last ones I bought came in direct from China and would take a couple weeks to receive, but...they won't help re-size female side contacts, only help release the contact from the connector, so...

    Just clean the pins, then spray with CDC electronic contact spray, don't coat them with anything else (the clamping force on the female contact is too low; di-electric manufs. don't recommend using it on low pressure contacts)...I've gotten out of the habit and just use CDC contact spray now.

    Gently burnish as best you can, then do the same on the terminal/male side, then apply di-electric grease on the connector shell halves where they mate as a seal. On the female side, just squeeze it down against a small diameter object, like a toothpick, so you don’t inadvertently crush it. Best solve when the contact is too far gone is to replace the wire end with a new contact.

    Did you open the harness side connector near the relays on the pass. side firewall, inside the engine bay, where the top left side engine harness connects to the body harness that leads to the PCM?

    Those are prone to corrosion and can inhibit signals/ref/return. I’d expect corrosion to raise resistance/lower volts, and a loose pin/contact, if clean, to cause an intermittent path, not necessarily high resistance. In other words i’d blame corrosion, first, and more likely, as opposed to a faulty connection, where there would be 0 resistance because of a break in the path. Not sure a loose pin would raise resistance….?
    Last edited by KMT; 03-15-2020 at 01:54 PM.

  15. #30
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    I did not open the clamshell on the PCM. I was able to verify that the 4.4K Ohm of bad resistance lives in the connector itself (in the engine bay)

    I'll be looking for that contact cleaner. 100% worst case I will bypass the connector for that single wire.

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