Low voltage at idle

[Devin LeBlanc]

I have noticed since I got my supra I have always had low voltage at idle well and while at RPM

With head lights, fog lights, and brake lights on I usually see 10.5 to 11.8 volts at idle.

I have tried 3 alternators, It has a brand new battery, Put it in 3 days ago. I have checked voltage drops from the alternator to the battery and it is only .1-.2 volts.

My SAFC is reading 10.0-11.0 volts at idle at the ECU power wire its tapped into.

Everyone else have low voltage at idle?

 

[bioskyline]

no on my neo, at high idle im at 13.8v, at low idle im getting 12.8. mind you everytime i hit my brakes my dash light go off, need to work on that one.

belts in good shape? are you pulleys stock or do you have a under drive?

 

[Devin LeBlanc]

Everything is all stock, Belts are brand new, correct tension, New alternator, new battery, Going to test resistance in the ground wiring and double check if there is any abnormal amperage draw with the key off

 

[bioskyline]

ok. but if you have all lights off is idle voltage normal?

 

[Devin LeBlanc]

According to the TSRM you put the headlights on with highbeams, and heater on high and voltage should be 14.6V at idle

My voltage is higher with everything off but not 14.6

 

[Travis89turbo]

Are you running a big stereo system? And have you tried a high output alternator? My voltage on my 1j dropped pretty bad as well but only to 12.2 with everything on and my amp! That is until I took it to my alternator shop and had them rebuild it to a High output. Which intels changing the bridge rectifier diodes to allow a higher voltage to go into the regulator which I had them change to an adjustable one. The adjustable regulator was originally designed for marine application but now I have a constant 14.3v at idle and throughout rpm.

 

[mkiiichip]

Your reading voltage on the SAFC, but what is the voltage at the battery while running?

 

[northwestsupra]

Agree get a dvom on that battery and check there.

Sent from my Droid using Tapatalk

 

[Poodles]

Grounds...

Also, what's your idle speed?

 

[bioskyline]

Are you running a big stereo system? And have you tried a high output alternator? My voltage on my 1j dropped pretty bad as well but only to 12.2 with everything on and my amp! That is until I took it to my alternator shop and had them rebuild it to a High output. Which intels changing the bridge rectifier diodes to allow a higher voltage to go into the regulator which I had them change to an adjustable one. The adjustable regulator was originally designed for marine application but now I have a constant 14.3v at idle and throughout rpm.

need more info on said adjustable regulator.

 

[jetjock]

Ugh. Must bite tongue...

 

[IBoughtASupra]

Regulator is inside the alternator. Grounds should be check. Battery to chassis and to the engine block.

 

[Devin LeBlanc]

I am not running a stereo system, I have checked voltage at alternator and at battery with a DVOM 11 volts idle with head lights on and blower motor on high..

Idle is 650 rpm's hot and like 1100 Cold. I have also checked voltage drop between the alternator output and the battery.

 

[Travis89turbo]

need more info on said adjustable regulator.

Like Iboughtasupra said its inside the alternator... but the regulator doesn't work as most think. It will lower the voltage but not raise it. So its basically a petentiometer or adjustable resistor. So if off the alternator out of the rectifier diodes (also inside the alt.) Is only 13v you can only adjust regulator less then that. But if u use upgraded diodes to say a 16v rectifier then it can be adjusted to the 14.4v. Now the stock diodes may not be the only problem. Brushes, magnets and all the other stuff goes out to so its best to get the whole alt. Rebuilt if NECESSARY! The company I had do it for me went out of business six months ago. ;-(

But you should always start with the grounds and other stuff mentioned above before replacing parts.

Also Check for corrosion at all the connections

 

[bioskyline]

Like Iboughtasupra said its inside the alternator... but the regulator doesn't work as most think. It will lower the voltage but not raise it. So its basically a petentiometer or adjustable resistor. So if off the alternator out of the rectifier diodes (also inside the alt.) Is only 13v you can only adjust regulator less then that. But if u use upgraded diodes to say a 16v rectifier then it can be adjusted to the 14.4v

ok that what i thought.

 

[mkiiichip]

JJ knows something obvious were missing.
Try grounding terminal F and see if the voltage changes. This basically bypasses the voltage regulator and puts the alt at max voltage. (for diagnosis)
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=CH&P=5

 

[Nick M]

I have no comment about your particualr setup and where you are getting your reading.

When current is flowing good, voltage reading will be lower. When there is high resistance to flow, voltage goes higher to push through the resistance.

 

[3p141592654]

http://www.engine-light-help.com/voltage-drop.html