Long story short.....I have been getting a code 42 intermittently for a few days now. At first I thought it was the wiring. It was looking pretty shabby so I went ahead and replaced the EST bypass wire (brown w/black) and the EST ground (black w/ red). The code only shows up in the morning after it has been cold at night. Once the car warms up it will go away provided that the motor is killed and then restarted. I am thinking about replacing the other 2 wires (White and blue???(I think)) on the 4 pin connector at the distributor. When the code does no show up I am getting 4.5 volts at the EST bypass wire with the engine running. I thought it was supposed to be 4.75, is this close enough?? When the code is there there is no voltage at the EST bypass wire. I am positive it is not a bad ECM. I have a spare and have already confirmed that the ECM is good. Main question: Could this be a bad ignition module? Wouldn't it be acting up all the time instead of acting up only when it has been cold??? Any ideas are appreciated.
bsa



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"If they do not run, Then they will die." - Stonewall Jackson
#3
'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Edelbrock Intake, Accel Runners, Comp Cam, Crane Gold rockers, Lucas 23# injectors, Edelbrock headers, Flowmaster 3'' exhaust, gutted cat, Mallory coil, Mallory HyFire IV ignition box, Mallory Sidewinder 8mm wires, Autolite platinum plugs, K&N filters, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter

 

BSA,

Typically, the digital logic of the ECM will recognize anything above 3.6 VDC as being in the "ON" state and anything below 2.1VDC as being in the "OFF" state without any problems. The voltages in between can be confusing for the ECM to resolve and can cause problems.

The EST signals the ECM with a digital signal, however (either on or off), so the 4.5 should be interpreted as "ON". Of course, non-digital (analog) signals to the ECM must have a lot better resolution, like that of the TPS, CTS, and MAF.

Still, the 4.5VDC could be indicative of a connection problem. Remember, however, that the ECM signal ground is not at exactly the same potential at chassis ground, so you should use an ECM signal ground connection for diagnosing all ECM-related voltages, not an engine or chassis ground.

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Later,
Vader
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"What a Day..."
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Vader, Good info, thank. Do you think the igntion module would cause these symptoms. I think I will just go ahead and have it tested/replace it today.
bsa