abuelijah

Hi all, after much searching and troubleshooting I'm lost on an alternator issue, so here goes the Hail Mary...

Just bought a 2000 RX300, 139000 miles for $400.

Seller said bad alternator, stuck a battery in, drove a couple miles down the road and back, engine and tranny seem solid. Battery down to 11volts on return, so i buy reman alternator from napa. Installed...still not charging. Alternator tests ok on the bench.
Continuity tested mega-fuse. tests ok.
Continuity tested Voltage regulator harness 4" behing plug. tests ok.
Alt-s fuse ok.
Gauge fuse ok.
Continuity tested Ground. tests ok.

Vehicle had been rear-ended slightly in the past, a little damage to the bumper. Shift lever was locked and i had to use the release button to get out of park.
I've installed and removed a new charged battery several times so i assume the ecu has been reset in the process.

What am i missing here guys? Thanks in advance!

Drcoffee

The battery should not discharge that fast even if the alternator is weak. There may be a big short somewhere draining the battery. Have you tried running the truck with the battery disconnected? Get it started and disconnect the ground terminal. If it dies, the alternator is dead even if it tests ok on the bench.

Also, charge the battery and put it in. Then check and recheck the voltage over a few days and see how fast it discharges.

$400? Was it in a flood

abuelijah

no flood, friend of a friend...[.. edit salim] needed cash immediately.

the alternator itself works. the battery is fine...the voltage reading was with lights on and ac running, thats not a battery discharge issue.

I'm down to trying understand how the ecu controls the voltage regulator...for example,

could there be something wrong with the ecu even though all other functions are normal?

could there be a set of aftermarket alternators that just wont communicate with the ecu?

Is there a workaround for the voltage regulator controls to get it working long enough to drive the hour home?

thanks again.

Drcoffee

Huh? You could not be more wrong.

The voltage regulator regulates the voltage (hence the name), not the ecu. The ecu trips a warning if the alternator is not charging. The voltage with the engine running and lights/ac on should be near 14v not 11v.

Here, read up on the charging system. I think you could use some help with basic understanding of how it all works.

http://my.is/forums/f221/diy-chargin...attery-426000/

I would also suggest you tow that car out of the area before the dude comes out of his drunken stupor and wants it back. [editing Salim].

salimshah

With due respect to DrCofee, do not run without the battery connected. [The battery keeps the voltage from spiking and prevents lot of electronics from getting fried. Exception is ... you know what you are doing].

I would start by checking the drain with everything shutoff.

Few general comments:
You may have lot of issues with the RX as the previous owner only wanted $400. (s)he may have had the problem diagnosed and figured it is not worth getting fixed.

The back of the RX has brake lights and the power is unswitched. Any partial short will keep draining. The same circuit also controls the safety release.

Salim

Drcoffee

BTW the ground continuity only checks to see if the ground is intact. If the ground wire is corroded, it may br connected but not working well enough to move 500 amps of current to run the truck and charge the battery.

Drcoffee

Good point regarding the brake lights. Salim, would pulling the fuse to the brake lights rule out a short there causing the drain?

I'm not sure I agree with you on the voltage spikes with the battery disconnected. The same wires from the alternator go to the fuse block as they do the battery. The battery isnt a buffer between the two. If the alternator sends a voltage spike, its going to hit both the battery and fuse block equally. But I could be mistaken.

abuelijah

i read that thread before posting, that's why i asked the question i did. Let me rephrase.

Is the alternator/battery/charging system a closed system? If the alternator and battery and grounds and fuses appear good should i look for a cause elsewhere on the vehicle? or should i go back and go through my tests again? like i said, all the components appear to work separately, but when i connect them together the alternator does nothing.

salimshah

Yes the best way to trace a current draw is to keep removing and reinserting fuses till a bad circuit is isolated.

The spike I am talking about is for general consumption. The battery prevents voltage from going higher than what it holds. Yes spikes can be prevented by not creating the spike condition and the learned/skill know how to handle it.

Salim

abuelijah

thats all well and good but i fail to see how a short can keep the alternator from working fellas.

does anyone have any insight into exactly how the alternator and ecu relate to one another? my problem seems to be related to the voltage regulator harness.

salimshah

I think we have a gap abuelijah. You are convinced that the alternator is bad and I have not reached that conclusion. My position is based on bench test of the alternator.

So humor me and answer these questions:

1. Is the discharge lamp lighting up?
2. What is the voltage at the battery terminal with engine off? And when the engine is running.


To answer your questions .. the alternator is a stand alone item with built in rectifier and regulator. When the diode (of the rectifier) goes bad, the battery gets drained out. It does draw current from the battery (for the field) and then uses mechanical energy to produce DC voltage.

Hope it helps.

Salim