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Old 11-02-2009, 08:22 PM
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Join Date: Sep 2009
Posts: 19
Default Electronic Spark Control module - '91, 5.7L

I'm in the midst of troubleshooting/verifying the Electronic Spark Control (ESC) module on my '91 5.7L. My Haynes manual shows most of the truck's wiring, but not the ignition circuits. Can someone provide a link or point me in the right direction to find the pinouts and color codes to the ESC module and the distributor? I have found a few write ups online, but a schematic or diagram would really be handy.

I've learned this much so far, by tracing wires with an ohmmeter.

ESC module wires: (It is a 5-pin connector, but only four of them are used.)
A - Dark Blue - (this may be the ESC "bypass" control line) - goes to ??
B - Dark Gray - This is Ground - goes directly to the engine block at an intake manifold bolt.
C - Yellow w/blk tracer - (This may be the wire that provides the REFERENCE pulse from the ECM; Used to trigger the ESC module to do what it does. That is, advance or retard the spark.) Goes to ECM (computer), but I failed to log the pin #.
D - Pink w/blk tracer - Goes to 12-pin ECM connector at location #5 on the top row. As near as I can tell, this is a switched +12 volt output from the ECM. There are only 23 ohms between this pin and pin #1 of the same connector where +12 volts comes into the ECM.
E - No Connection

If anyone can fill in some of the blanks or provide additional info on the ESC circuit, I would appreciate your help.

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Old 11-03-2009, 07:33 PM
Toyota, Nissan, and Other Truck Forum Moderator
Join Date: May 2009
Location: West Texas
Posts: 1,845

Look on the passenger side of the engine and you will see a electrical spout with a Grey square module plugged inside. That is the ESC. You take it out to check and set timing.
That way you'll Learn!!!!
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Old 11-04-2009, 04:17 PM
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Join Date: Sep 2009
Posts: 19

Thanks for the reply Ruffneck. Are you referring to this gadget?

Because this is what my Haynes manual and Autozone say the ESC module is. You're right. It is on the passenger side, near the air filter. Actually, finding it is not the problem. Determining its functionality and troubleshooting it IS the problem. I've been looking for a wiring diagram or schematic that shows how it is wired into the system. I have found a couple write-ups online that explain when it is used or bypassed by the computer, but a schematic is worth a thousand words.

What I've found so far is pointing to my ESC module (or its wiring) as possibly being defective, but I'd like to "test" it in some way so that I can be more definite about my conclusion before I lay down $70.00 for a new one.

Have you found any good online sources for schematics and such?
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Old 11-04-2009, 04:17 PM

350, advance, chevy, circuit, control, dodge, electric, electrical, electronic, esc, gmc, mod, module, silverado, spark

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