Nuyota

This is 1987 4runner sr5 turbo. The truck has always had intermittent slightly rough idle, usually when starting while warm. It has new plugs, rotor, wires, battery, alternator, etc. I've had a voltage meter on for a while and been wathing it. When first starting it's solid between 13-14, and when driving or whatever it's usually around 12.5 or higher. Sometimes, usually after starting while warm, the voltage will show 12.5 or under. This is when it starts to idle rough, and if it drops under 12 it might die. I can't figure why it would do this at different times.

stanprophet

Most likely it is an indication of a voltage regulator or rectifier diode failure. One way to test it is to start the truck up and measure the voltage like you have done. Then at idle with no loads on, turn the multimeter to A/C volts, and measure across the battery. Should be well under 100 mv or .100 volts.

Then turn on the high beams, and turn the blower on high. Measure the dc volts, then switch over to A/C and make sure the voltage is less than 300 mv. Then have someone bring the idle up and check the same thing. It really should maintain 13.2 volts or higher even with the loads on.

If the A/C is more than .300 mv at the battery, you have a bad diode in the rectifier bridge. If the A/C is fine, but DC is falling off it is possible the voltage regulator is bad. But do not rule out a bad battery. A sulfated cell can still produce enough current to start the vehicle, but cause voltage supplying the regulator to change how it is charging. Might be wise to hit autozone or somewhere that has a decent capacitive battery and charging system analyzer. Inspect the wires on the round plug on the alternator, make sure they are not burned or chafed. Also make sure the battery terminals are clean, tight, and the connection to the cables are fine.

Nuyota

Ok I will check with the meter. From the readings I have so far it definitely doesn't maintain over 13V at all times it dips down. I had the issue with the original battery, and have tried two other new batteries, plus I put new terminals on also. My grounds coming off battery to engine and chassis are good too. Is voltage regulator and/or rectifier diode integral to the alt or seperate parts?

wyoming9

iTrader: (1)

Those parts are in the alternator.

Lets do simple first !!

Is by chance the alternator belt loose??

Just what rebuilt alternator did you go with ??

The specs on the battery ??

Just how do you know your ground cables are good??

You might also want to check the wire coming off the B terminal of the Alternator( single wire goes to fuse block) these have a habit of dieing from old age.

You say you replaced battery terminals with just what kind??

You did mention tune up did you just forget the air filter and distributor cap the fuel filter when listing what was done.

What brand wires I have had some run poor till I switched to Toyota wires.

Running the correct plugs