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Discussion Starter · #1 · (Edited)
I have a 1985 GLH converted to T2 GLHS specs and I have been experiencing a lean condition when I start the car cold. When I start it cold, it will go lean on the wideband, sputter, and eventually die. To troubleshoot, I back probed the coolant signal wire at the LM to get voltage readings. Here is what I found:
  • When the car has been sitting overnight, the coolant signal wire at the LM reads 2.5V with the ignition key on (not running)
  • When I start the car, the voltage on the coolant signal wire will begin to drop. After about 30 seconds or so of running, it will drop below 2V.
  • After the car runs for about 1-2 minutes, the coolant voltage jumps to 3.8V which is the voltage I would expect to see given the temperature of the coolant at the time.
Has anyone experienced this behavior? I did check 2 other different coolant sensors with the same result. If I plug in a new coolant temp sensor without it being installed in the head, shouldn't I be reading 4V? Everyone I have tried thus far has stated 2.5V. What would cause the voltage to jump to the correct level after the car has been running for a period of time?
 

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Discussion Starter · #3 ·
Thank you very much for the great explanation. I was under the impression that my lean cold start condition under due to low coolant sensor voltages. I will continue to troubleshoot but at least I know this is not a problem.
 
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