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Discussion Starter · #1 ·
Going to replace my ECM,
According to TPS test that was the results. High voltage on blue wire and all wire circuits are good.
Thought of getting a used one off EBay or remanufactured from auto parts store online
not sure what goes bad with ECM’s
Has anyone had this issue or luck with a used one or is it risky, $30-$60, buck used $100+ Remanufactured
Not sure if that will fix the problem
 

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Discussion Starter · #2 ·
Going to replace my ECM,
According to TPS test that was the results. High voltage on blue wire and all wire circuits are good.
Thought of getting a used one off EBay or remanufactured from auto parts store online
not sure what goes bad with ECM’s
Has anyone had this issue or luck with a used one or is it risky, $30-$60, buck used $100+ Remanufactured
Not sure if that will fix the problem
Question
Does the check engine light indicate a bad ECM, is other ways to tell it’s bad has anyone had a bad ECM?
Don’t want to buy parts I don’t need
thx
 

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What kinds of symptoms are you experiencing that say change ECM? What code specifically to says change ECM? Usually a bad ECM would translate to engine performance issues or a whole bunch of issues.
 

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87 Caballero Amarillo, stock 305/200R4/QJ
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It's a Chevy, not a Ford. Replacing the ECM is a last resort. Being inside the car vs under the hood, they take far less abuse and almost none from the elements. I'd be wanting to know the codes and/or behavior and possible reasons why the ECM may be bad, before changing it.
 

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Discussion Starter · #6 ·
You can watch/count the blinks to find the code if any exist. Sometimes the ECM may have gotten hot and you can see the warpage and/or if it has taken on moisture over the years. The ECM is in the passenger side kick panel.

It's a Chevy, not a Ford. Replacing the ECM is a last resort. Being inside the car vs under the hood, they take far less abuse and almost none from the elements. I'd be wanting to know the codes and/or behavior and possible reasons why the ECM may be bad, before changing it.
Curious if you have had to replace your ECM?
And the reasons why and how you were brought to that conclusion?
Want to know what are different ways they can go bad. Electronically
Besides weather damage or age
Thx
 

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87 Caballero Amarillo, stock 305/200R4/QJ
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I've replaced only one, in a 74 dodge dart sport. It had a capacitor go bad and leak out. With those older ecms, they were much simpler in design, no can buss, no bcm or pretty much other electronics. And physical sensors like the O² and oil pressure sensor etc. So realistically there's a whole lot less stress and things that can go wrong, as long as the individual components hold up after this many years.

I'd be more inclined to believe the TPS is bunk before an ECM. What were the voltages, and from where?
 

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Discussion Starter · #8 ·
What kinds of symptoms are you experiencing that say change ECM? What code specifically to says change ECM? Usually a bad ECM would translate to engine performance issues or a whole bunch of issues.
GM service manual checking TPS, sensor and wiring OK. Still High voltage 417 blue wire, manual says everything checks out replace ECM, burns rich won’t idle guzzles gas
 

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Discussion Starter · #9 ·
Buying a remanufactured or a used ECM, is my concern, a used one you take your chances but there cheaper, a remanufactured is like new slim chance of problem's but twice the cost.
Not sure what breaks or goes bad with them
Any thoughts
Thx
 

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High voltage on blue wire and all wire circuits are good.
By blue wire do you mean terminal 18 to the carb solenoid? If so, before replacing the PCM check:

ALL power inputs to the PCM for 12 volts
ALL grounds to the PCM (should have 0.1 volts or less)
Carb solenoid resistance (should be 10 ohms or more)

Here's more on carb solenoid resistance:


If you've already checked these items during your wire circuit check, then I agree the PCM is suspect.
 

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Discussion Starter · #11 ·
By blue wire do you mean terminal 18 to the carb solenoid? If so, before replacing the PCM check:

ALL power inputs to the PCM for 12 volts
ALL grounds to the PCM (should have 0.1 volts or less)
Carb solenoid resistance (should be 10 ohms or more)

Here's more on carb solenoid resistance:


If you've already checked these items during your wire circuit check, then I agree the PCM is suspect.
 

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Discussion Starter · #12 ·
Test is for TPS, GM service manual test concludes if all circuits are good and voltage is over 2.5 volts,,, on blue wire 417 which controls idle, then replace ECM.
Carb is new rebuild a year ago
 

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Test is for TPS, GM service manual test concludes if all circuits are good and voltage is over 2.5 volts,,, on blue wire 417 which controls idle, then replace ECM.
Carb is new rebuild a year ago
Terminal 18 is circuit 411 (Lt blue wire), so that does not apply to your checks.

Looking at circuit 417, the 5 volt sensor circuit or bad sensor ground could cause a a voltage over 2.5 on 417. Do you have the readings for all three TPS terminals? Does circuit 417 read more than 5 volts?
 

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One wire should be about 5 volts, one ground, and one will vary with throttle position, from about .6-.8V at idle to 4.5v at WOT. I no longer have my manuals, so can't tell you which wire, but I think the center wire is the one that changes with movement. Measure to a known goo ground. Measure with the key in run position, but engine off.
 

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Discussion Starter · #17 ·
One wire should be about 5 volts, one ground, and one will vary with throttle position, from about .6-.8V at idle to 4.5v at WOT. I no longer have my manuals, so can't tell you which wire, but I think the center wire is the one that changes with movement. Measure to a known goo ground. Measure with the key in run position, but engine off.
According to test, manual says it’s the ECM, getting a remanufactured from Cardone AP.
thanks very helpful appreciate it.
 
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