Final Resistance Measurement of Failed ECT sensor confirms off the FSM chart reading
You know, it's always nice to get the chance to acknowledge someone in public for going above
and beyond in order to share solid failure data that can be used for future troubleshooting by
the GMT400 community.
After Beason troubleshot his non-starting TBI truck to a bad Engine Coolant Temperature
sensor & got it running, I asked if he could send the sensor to me so that I could see if I could
get a steady reading out of it with my FLUKE? (In the video his meter was constantly autoranging
and we couldn't see exactly what resistance his sensor was vs the temp/resistance chart in the FSM?)
In order to set the stage, here's the ECT temp/resistance chart one more time:
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And here is Beason's sensor at 72 degrees F on a FLUKE 117:
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Almost 1.7 Megohms (on a 0-6 Megohm scale) vs the correct measurement at 72 degrees: ~3,200 ohms
If the sensor had shorted out internally, the computer would be misinformed that the engine coolant was above 212 degrees F,
and would starve a cold engine for fuel, making for difficult starting at winter temps.
But since this sensor failed 'open', the computer is misinformed that the engine coolant is -40 degrees F,
so the computer commands an extremely rich A/F ratio. (~2:1, instead of 14.7:1 stoich all warmed up.)
This would help to explain why the TBI injectors looked like shower nozzles even at cranking speed. (!)
NOTE: I am confident that this is a valid measurement. The initial reading was in the ~1.65 Megohm
range, and drifted up over a short period of time before it stabilized here. (Thinking the internal
bits, although busted, were still reacting ever so slightly to the voltage applied by the meter?)
****
I just wanted to see if we could get steady readings from Beason's 'engine proven bad' ECT sensor,
and then leave it here for future troubleshooters. But I couldn't have done this without this fine
Texan taking the time & effort to send the failed sensor up my way here in the Finger Lakes region of NY.
Tip of the hat towards Houston. Nice team effort.
Cheers --
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