ECM says it reads 21.1v all the time
01-26-2009, 07:32 PM
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Car: 76 Nova
Engine: 350
Transmission: 700R4
ECM says it reads 21.1v all the time
I've been chasing a few issues. My data stream reads 22.1 volts all the time. Battery and alternator voltage is normal 14.58v running and 12.48 key on engine off. Of course it's setting a 53 and going into limp mode. Dosent mater if the alternator is plugged in or not.
All I can think is I have a faulty ECM. I checked the main grounds and voltage at the alternator, battery and starter. I can't think of any reason the ECM could legitimately see almost 10v over measured battery voltage.
Any ideas?
All I can think is I have a faulty ECM. I checked the main grounds and voltage at the alternator, battery and starter. I can't think of any reason the ECM could legitimately see almost 10v over measured battery voltage.
Any ideas?
01-26-2009, 08:17 PM
#2
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Car: 83 POS monte carlo 2015 chevy P/U
Engine: 92 5.7 tpi 5.3
Transmission: 700r4 6L60E
Axle/Gears: 2.42 too high
Re: ECM says it reads 21.1v all the time
i don't know what your using to scan it with, but if you have used the same tool in the past and it read the voltage right, you ECM is dying.
01-27-2009, 12:26 PM
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Car: 76 Nova
Engine: 350
Transmission: 700R4
Re: ECM says it reads 21.1v all the time
It's an old OTC monitor 4000. IT's always been reliable in the past. When it shows the high voltage, the pins at the ECM show 12.28 volts. It keeps setting the 53 too. How does the ECM calculate the voltage? Just a reading or is it more complex than that?
01-28-2009, 08:06 PM
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Car: 83 POS monte carlo 2015 chevy P/U
Engine: 92 5.7 tpi 5.3
Transmission: 700r4 6L60E
Axle/Gears: 2.42 too high
Re: ECM says it reads 21.1v all the time
that OTC 4000 is a good scanner, i used one for years.
i don't know how it comes up with the voltage, but im pretty sure its calculated somehow.
in every case i have ever seen where the ECM reports a higher than normal voltage and the charging system is good, its always been the ECM.
when ever i see the reported voltage higher than about 1~2 volts higher than system voltage, i won't do any more tests without first replacing the ECM.
i've seen one report as high as 50 volts, but most have been in the 17~25
volt range.
i don't know how it comes up with the voltage, but im pretty sure its calculated somehow.
in every case i have ever seen where the ECM reports a higher than normal voltage and the charging system is good, its always been the ECM.
when ever i see the reported voltage higher than about 1~2 volts higher than system voltage, i won't do any more tests without first replacing the ECM.
i've seen one report as high as 50 volts, but most have been in the 17~25
volt range.
01-29-2009, 05:39 PM
#5
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Car: 76 Nova
Engine: 350
Transmission: 700R4
Re: ECM says it reads 21.1v all the time
that OTC 4000 is a good scanner, i used one for years.
i don't know how it comes up with the voltage, but im pretty sure its calculated somehow.
in every case i have ever seen where the ECM reports a higher than normal voltage and the charging system is good, its always been the ECM.
when ever i see the reported voltage higher than about 1~2 volts higher than system voltage, i won't do any more tests without first replacing the ECM.
i've seen one report as high as 50 volts, but most have been in the 17~25
volt range.
i don't know how it comes up with the voltage, but im pretty sure its calculated somehow.
in every case i have ever seen where the ECM reports a higher than normal voltage and the charging system is good, its always been the ECM.
when ever i see the reported voltage higher than about 1~2 volts higher than system voltage, i won't do any more tests without first replacing the ECM.
i've seen one report as high as 50 volts, but most have been in the 17~25
volt range.
Thanks I feel better knowing it's happened before. I've never seen it. I'm going to swap the ECM and hope fully the misfire is gone too.
01-30-2009, 09:40 PM
#6
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Car: 76 Nova
Engine: 350
Transmission: 700R4
Re: ECM says it reads 21.1v all the time
In case anyone does a search in the future, the ECM fixed the issue.
DENN_SHAH thanks for the replies.
DENN_SHAH thanks for the replies.
01-31-2009, 04:39 PM
#7
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Car: 83 POS monte carlo 2015 chevy P/U
Engine: 92 5.7 tpi 5.3
Transmission: 700r4 6L60E
Axle/Gears: 2.42 too high
Re: ECM says it reads 21.1v all the time
no problem 
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01-31-2009, 08:23 PM
#9
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Car: 76 Nova
Engine: 350
Transmission: 700R4
Re: ECM says it reads 21.1v all the time
It seems to be gone, but I'm about out of fuel. I just moved to AZ and the car isn't insured or registered here yet so I can't just run over and get some. I only ran it for 10 minutes or so. It smoothed out and I got equal temps at the header pipes once it went into closed loop, but it's been a weird intermittent where it will miss steady and then run smooth for a while. The BLM went to 148 pretty I think there are issue with the tune. Ultm8z is going to walk me through that end of it here in a couple of months and get me up to speed.
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