99custom

So I just replaced the alternator in my 02ES300 with a re-manufactured Denso. I also replaced the pigtail due to corrosion. My battery was low as well so I had it checked at the parts store (O'Reilly's) and recharged. Here's the deal,The car will start and run just fine with a voltage reading of about 14.25. After I put a load on it, turn on the A/C it drops to about 14.05 or so. After about 5 minutes it's all the way down to 12.5. I checked the alternator fuse and that was good. I got a b-post reading under .1 (it was .6). I can't get a reading off the alternator casing because it's painted and I don't want to sand a spot off in case I have to return it. I have sanded the battery cables and terminals and I'm getting a good reading from them. I really don't know what's going on...

Other things to note... The idle needs to be reset since I had the battery disconnected, I haven't down this yet since the readings are poor. I'm not getting a battery light on the car dash yet. My power sterring pump is on it's way out (that was next project).

Any help would be greatly appreciated.

Update- Alternator tested by the parts store and it failed the test, it has BAD DIODES... That's disappointing coming from Denso...

99custom

Update..I rest the idle and the voltage went back up to 14.00. I went driving for about 10 minutes with the A/C on but when I came back it had dropped back down to around 12.5. I'm totally stumped....

99custom

update...Did a milli volt test and was well under 50.... Now with car running it just stays around 13.8-14 but as soon as the ac turns on it starts dropping back into the mid 12's.

Should I pull the alternator back out and take it to get tested?

Oro

If you can drive to the store, they can test it in the car. This presumes all your ground wires are good - have you checked the actual terminus of your battery ground and cleaned/sanded it?

Honestly you can test it yourself. At idle, is it producing over 14 volts as measured at the battery terminals? When you rev the car, does that voltage stay the same or increase a bit but stay under 14.5/6? If so, your brushes are making good contact and making juice. Your voltage regulator is converting that to managed DC voltage for your battery correctly.

If not, then it may be the alternator, it may be a bad ground, it may be an internally grounded battery. If you are measuring your battery with the engine turned off and the voltage reads 12.5v, that means the battery is at around 80% charge and the majority of the batteries out there are likely at that level as we speak. If it is an older battery, that well may be full charge for it. Driving it for a few minutes won't change that much at all; it has to run longer or be charged off-car to get to full charge (12.7v or a bit more).

I'm not really sure there is a problem here as you weren't entirely clear if the readings were with the car running, switched off, or ignition on and engine off. For different conditions, any of the readings you stated above would be normal. Even if normal, I would clean the grounds as Arizona climate + corroded alternator wiring = Unlikely.

99custom

The readings for the alternator are when the car is running. I'm getting 13.8-14 steadily while running but when I turn on the A/C it drops all the way down to 12.5 within minutes (still running). When I shut the car off the battery needs to be put on my trickle charger as it's low around 12.2-4. The battery was fully charged when I started (charged at parts store). Every other time I swapped an alternator (in the past) it would read at 13.6-14.5 depending on the load. 12.4 or less seems really low.

I did clean and sand the battery terminals and connections as well.

I also just did this diode test from youtube....It said I should I have a reading between 500-800 and 1, and my alternator reading was 440 and 1. Does this mean one of my diodes could be bad since my # is low.


Thanks for any suggestions or help...

LeX2K

Which alternator exactly did you put in? Instead of turning on the A/C put the fan to high headlight switch on and test the voltage at idle. What rpm is the engine with the A/C on?

99custom

I put in a re-manufactured Denso from Amazon . If I don't turn on the A/c it will only drop to 13.4-13.6, but when the AC is on it just drops to 12.4 or lower depending on how long I let it idle with the air on. I'm going to drive up to the parts store and have them test my alternator while it's still on the car. I'm just pretty frustrated.....

99custom

Took it up to O'Reilys and it failed the test, bad diodes. Can't believe Denso sent me a bad alternator. I learned the lesson of always have your new alternator checked before you install it. Thanks for the replies.....

LeX2K

That's disappointing not to mention bad luck.

Htony

Alternator is an AC generator. 3 pairs of diodes forms full wave full wave 3 phase rectifier to output DC current. If a diode(s) is bad output won't be a good DC current. If you tune AM radio how does it sound? Is he battery known good?
At this point I think you need to replace battery and repair the alternator or get a good alternator If ground cable has poor connection floating alternator can even ourtput much higher voltage burning out everything
in the car. If OP is not familiar with basics in electronics, be careful dealing with problem like this. For good trouble-shooting you need old analog multimeter which has low input impedance and a DC current meter.
which can read high Ampare value. If you have an oscilloscope or can borrow one you can visually see the wave form of alternator output.

Oro

So hold on a minute, no doubt it's a bad alternator, BUT - a genuine Denso rebuild would not fail like this.:

You bought it direct from Denso? Because a lot of people sell rebuilt Denso alternators. Since they are the OE, people take the cores, polish them and paint the pulley, put in new brushes and re-sell them. They totally ignore the voltage regulator, windings, etc. The vendor was actually either Denso, or they told you it was a licensed/genuine Denso rebuild? Or the simply said they rebuilt a Denso core? Where did you buy it?

Second, and this may disappoint you, but this is q totally normal experience with rebuilt alternators. They are not properly rebuilt, even the ones you get from O'Reillys and Autozone. They are just lowest cost packaging from Mexico with cheap Chinese components. If you got this from Napa, or genuine brand Denso rebuild, I can see some disappointment. Otherwise, Honestly, you got what you paid for.

Either rebuild the alternator yourself (very easy to do, no serious skills or great cost involved), or get it rebuilt at a local auto electric shop. I am sorry you have fallen prey to the general auto electric scam that cheap Chinese parts and lowest-price point shopping has created, but this is not a secret to anyone who reads this forum or does a little internet research before buying.

LeX2K

You didn't see the Amazon link he posted?

PFB