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Toyota Service
Toyota Service, Lexus and Toyota expert
Category: Lexus
Satisfied Customers: 4612
Experience:  30 + years of experience; Multiple Award Winning Svc Mgr; Just Answer Customer's Choice Award Winner
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Another question regarding my motor swap... I have my

Customer Question

Another question regarding my motor swap... I have my alternator wired up per the Toyota wiring diagram. The Alternator is not charging the battery while the car is running. The alternator is a newly rebuilt unit. I had it installed and experienced the same problem so I pulled the alternator and had it tested at the electrical shop that pulled it. The alternator functioned properly. I re-installed the alternator and and this time just to test the alternator I took the connections directly from the IG and S terminals of the alternator and connected them directly to the alternator output lug. I ran an additional wire from the L (dash light terminal) to the charge light. I also have the alternator main lug hooked up to the battery. When turn the ignition switch to run that charge light illuminates as it should. When the car is started and running the charge light goes out indicating that the alternator is functioning properly. However, there is no output from the alternator.
Submitted: 17 days ago.
Category: Lexus
Expert:  trung do replied 16 days ago.

HI THIS IS TRUNG . DIDN'T U CHECK THE VOLTAGE AT THE TERMINAL AT THE ALTERNATOR SIDE

Customer: replied 16 days ago.
with the engine running it's 11.98 with the engine off 12.35.
Expert:  trung do replied 16 days ago.

if voltage is below 12 the alternator is not charging correctly . if you check at the alternator it 11.98 can u check at the battery terminal to see how much voltage drop is running thru the wire for me . if to much resistance in the positive terminal this can cause issue as well

Customer: replied 16 days ago.
The voltage is the same at the battery. This is a motor swap and the installation is brand new. There is no output from the alternator. Please read the initial question for a full description of everything I have done.
Customer: replied 15 days ago.
Do you have any other advice?
Customer: replied 15 days ago.
Do you have any other advice? Based on my original question and supplied information the advice i received was information that I already knew. Please help me.
Expert:  trung do replied 15 days ago.

if alternator is giving out 11.98 voltage at alternator terminal that is a bad alternator

Expert:  trung do replied 15 days ago.

I will optout let other answer

Customer: replied 15 days ago.
I watched it be bench tested 3 days ago. It put out 14.2 on the bench. Ok thanks for your time.
Expert:  Toyota Service replied 15 days ago.

Hello.Customerhere. The issue here might be the RPM of the test bench vs the RPM at idle installed on the car. In order for the alternator to produce sufficient output voltage, the unit needs to put out 14.4 volts DC at roughly 600-650 RPM. If the test bench spun the alternator RPM up over 600-650 RPM, the alternator would test 'good', but ultimately fail in reality because it needs to be at 600 rpm, nothing more during the test. Now, let's turn to the engine RPM. If you are not idling at at least 600 rpm, you are going to have a low voltage output. If your engine is turning 600-650 at idle, and a 'good' alternator is fitted, it should put out 14.4 volts. 11.98 is too low, unless you have a huge parasitic draw occurring (large audio amplifier turned on, high output headlights on, etc.). The alternator measurement should be done with all of the electrical draw accessories (lights, radio, etc) OFF when testing. Assuming your engine is indeed turning 600 rpm at idle, I suspect either a slack drive belt or a faulty alternator.

Customer: replied 15 days ago.
I have used a shim on the throttle body to bring the motor up to 1500 RPM. I tested the output with a voltmeter at that time also and no change from idle. I have considered the belt since I am not running a stock serpentine belt pattern. But, I can tell the pulley is rotating by visually watching it.
Expert:  Toyota Service replied 15 days ago.

Does the voltage increase when the RPM is above 2500?

Expert:  Toyota Service replied 15 days ago.

wait

Expert:  Toyota Service replied 15 days ago.

Maybe the alternator is running backwards! That would cause this .

Customer: replied 15 days ago.
Not that I can tell by my gauge and I haven't tested it with a voltmeter at that engine speed. The gauge is unaffected at any engine speed. However when I switch on the engine cooling fan I can see the draw on the system via the gauge. So I know it's working.
Customer: replied 15 days ago.
I thought alternators didn't not care about direction of rotation. At least that's what I have read elsewhere.
Expert:  Toyota Service replied 15 days ago.

If the bench is testing at 14 and you have 11, it is highly possible. They may not 'care' which way, but, to get optimum output, it needs to go the way it is designed. Ask the alternator tester which way he spun it. See if it spins the same way on your car.

Customer: replied 15 days ago.
Ok will do. I will check back with you to see if that solves the problem.
Expert:  Toyota Service replied 15 days ago.

ok. And please make sure that you belt deflection (where you push on it with your finger) does not exceed 3/8".

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