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Need expert-level PCM/Electrical help with ECT and O2#1 CEL's (#116 KOER only and #176 KOEO only)

Discussion in 'Stock 1991 - 1994 Explorers' started by Craggles, December 27, 2017.

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    1. Craggles

      Craggles New Member

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      Year, Model & Trim Level:
      1993 Ford Explorer XL 4WD
      Background:
      - 1993 Explorer 4.0 XL 4WD; 225K Miles.
      - I bought new in 1993, still in the family but I haven't driven it for years until recently.
      - Has been driving with ice-cold Temp Gauge and CEL(s) for years.
      - Likely, the #116 and #176 I pulled out recently using the paper-clip method!
      - My '93 runs quite well! But the MPG is in the toilet... (~15MPG). I'm old, and drive like it. But I will certainly use the 4.0 when necessary :)

      - My question right now is about sensor resistance, and sensor and reference voltages I have measured at the PCM under various, which I provide details on below.
      - The initial Troubleshooting information here is for completeness.

      - See attached Electrical Schematic; it's the only thing I'm working to... (Thank you, also, for the suggestions re. better versions) :)

      - NOTE: In the schematic please notice that the ECT sensor and the O2 sensors, along with some other sensors, share a common GRY/RED wire.
      [NEW THOUGHT GENERATED...!!] what if "an other sensor" is jacking the common connection...??!!)

      - Also notice the GRY/RED wire goes to Pin46 of the PCM. (The outputs from all of the sensors have their own inputs. The ECT is on Pin7 and O2#1 is on Pin46.

      Troubleshooting:

      - First, I confused the Temp Gauge with the ECT CEL's and was troubleshooting the wrong sensor. After being corrected by Roscoe (Thanks!), I was back on track.

      - Also first, I was concerned that in my absence the thermostat was removed. But I started-up and heated-up the engine with the radiator cap removed while observing the water in the radiator. The water was "still" until the thermostat opened. While the water in the radiator at that point registered approximately 190deg on a meat thermometer, it did feel cool to the touch. Even when I stuck my finger way down inside, I could not burn it so it did not FEEL like 190... Pressing onward (and, I have new information below which shows the 'stat is indeed at least opening and closing...)

      - Second, checked fuses, including #18 10Amp for the O2 sensors.

      - Third, I replaced BOTH O2 sensors and the ECT. No change in CEL's. (actually but sadly, my expected outcome. But, they were OLD anyway :)

      Although I did get some initial excitement re. the #176 (KOEO only). When I ran the test right after changing the O2 sensors, the #176 did not show up.
      Yaaay. Whoops. It showed up the next time I did the KOEO test, after doing a KOER test .... no idea!

      - Fourth, I measured the electrical resistance of both wires from the ECT to the PCM; both zero-ohms. Also measured for shorts to Gnd and 12V. It turns out the GRY/RED wire, common to the ECT and both O2 sensors, measures zero-ohms to Gnd. (We'll definitely come back to THAT...!!)

      - Fifth, I cut the GRY/RED wire near the PCM for access. The Lt GRN/RED wire from the ECT was already cut, due to my earlier debacle while confusing the 2 temp sensors :)

      - Sixth, I measure 3.15V at the ECT sensor input and quite oddly, about 0.5V on the common GRY/RED wire. Remember, this wire was "shorted" to Gnd.

      - (almost) Lastly, I went out for a drive while monitoring the ECT sensor voltage, which started "cold" at 3.15V (which SEEMS low as a starting point, given that the sensor voltage goes down as Temp goes up...)

      - Then I measure the ECT resistances, HOT and COLD.

      Results:

      (disclaimer: I am an electrical engineer with many decades of experience with sensors, computers, etc. That said, in case you hadn't noticed, I'm frequently wrong. It makes me a better engineer... :)

      - In my mind, the test confirmed the correct operation of the cooling system and sensor operation. The sensor output closely followed the warm-up and driving conditions and also showed the opening and closing of the thermostat. Detailed output here:

      ECT Voltages
      Cold; 3.15V
      Hottest; 0.97V
      Thermostat; 1.15V

      So, Here are my most recent thoughts:

      The GRY/RED wire common to sensors at Pin46 is actually "floating". In electrical terms, it is NOT being driven by Pin46 of the PCM. I conclude this because as I said I understand sensor systems; it could be a Gnd, or more likely a Ref Voltage (which, again Could be 0VDC). But no Ref voltage should EVER be floating!

      And, here's the expert-level help I need...

      Does anyone know, or can someone who's NOT getting these errors measure, the voltages at Pins #7 and #46 with the engine cold and the key on...?? (you don't have to snip the wires :) just use a push pin through the insulation. Low voltages and inside the cab = no risk...) And sensor voltage HOT would be an absolute GROOVE!

      Another piece of useful information would be the Cold/Hot resistance of the ECT sensor, but the voltages are more useful. My new ECT; 5.7Kohms COLD, and 3.28Kohms HOT.

      >>>>> BUT DON"T ATTEMPT ANY OF THIS UNLESS YOU KNOW WHAT YOU"RE DOING...!!!!!

      Even better if someone already knows the answer. Any Ford mechanics or Electrical Techs out there?

      Just so you know, I also tried actually hard-wiring the GRY/RED to Gnd. No help.

      Now, I'm going to eliminate any ill effects from the "other sensors" on that line. Here's the schematic:

      upload_2017-12-27_11-34-8.png
       
      Last edited: December 27, 2017
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    3. TDG

      TDG Elite Explorer

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      I can do that (I'm not getting any codes) do you want those pins measured between each other or each referenced to ground?
       
    4. roscoe 0202

      roscoe 0202 Elite Explorer

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      craggles
      thanks for the information on grey red wire I've got a 92 4.0 going into a 84 bronco II can't find where that wire goes left it long and tied to bundle thought about grounding but apparently that is not where it goes.
      roscoe
      p s I don't think it is power power seems to be coming from passenger side to engine.
       
    5. roscoe 0202

      roscoe 0202 Elite Explorer

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      got warm enough today to get out wiring diagram it is for a 91 but shows grey red wire goes to neutral sensing switch.
      roscoe
       
    6. TDG

      TDG Elite Explorer

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      My test results (cold) mirrored yours - the only exception is that my ECT senor shows 13.6KΩ when cold, (2.94KΩ hot) key off and sensor connedted to the EEC. Assuming that you took this measurement with the sensor connected to the EEC there is a certain amount of influence the electronicals inside of the EEC are having on the measurement.

      Disconnected across the EEC I had a resistance of 20.41KΩ (Cold) measuring the electronicals of the EEC

      Disconnected across the sensor I had a resistance of 62.6KΩ (Cold - the low was in the high 40s here last night and that resistance reading is about where the sensor chart says it should be - 58.75KΩ at 50 degrees F and 1.18KΩ at 248 degrees F)

      Voltage cold = 3.141

      Voltage hot = .614 (the sensor charts indicates .61v = 194 degrees F and I have a 190ish thermostat installed)

      Your hot reading of .97 indicates that your engine temp is somewhere between 158 and 176 (158F = 1.04 and 176F = .80)

      My GRY/RED showed 13Ω to ground with key off, with key on it went to 300Ω and drifted back down to 130Ω or so.
       
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    7. TDG

      TDG Elite Explorer

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      As to the lean code / 176 issue - have you tried putting a scope on the 02 sensor input to the EEC for bank 2? (I think it's pin 43 and 44 depending on which sensor you want to read) to see if the sensor is cycling correctly? It's been awhile since I've messed about with 02 troubleshooting but I believe low voltage will indicate a lean condition and high voltage a rich condition.

      Attached is a waveform from my 93 between pins 46 and 44 at hot idle - I have no codes and this follows what would be considered a 'known good' waveform of 4 wire 02 sensors from other sources.

      My 02 sensors 'woke up' after about a minute from a cold start and began cycling as below - they are also both brand new quality sensors.

      93 Ford Explorer O2 Sensor 1 idle data.PNG
       
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