Craggles
Member
- Joined
- December 18, 2017
- Messages
- 12
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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:
- 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: