Charging Problem

[vltjr]

My '91 LS400 died this morning while my daughter was driving to school. The first symptoms were that the dash lights flickered and then got dim, then the radio cut out, and lastly the car died. After I got the car home I charged the battery, and the car started, and everything worked normally. My question is: how do I determine where the problem is? How do I test the voltage regulator separately from the alternator? Any help will be greatly appreciately.

[Jerry Bransford]

My '91 LS400 died this morning while my daughter was driving to school. The first symptoms were that the dash lights flickered and then got dim, then the radio cut out, and lastly the car died. After I got the car home I charged the battery, and the car started, and everything worked normally. My question is: how do I determine where the problem is? How do I test the voltage regulator separately from the alternator? Any help will be greatly appreciately.

With those symptoms, I would be more inclined to believe it's the battery that has gone bad, even though you charged it at home. Have the battery "load tested" which will show its true condition. A car will barely run, if at all, once the battery goes bad even after jump starting it. This is because an alternator requires an "exciter voltage" from the battery so when the battery goes bad, the alternator stops putting out power and the engine will die.

For those who may say it won't die once the battery goes bad, you're thinking of the old days when cars used generators instead of alternators. Generators don't require a battery, you can remove the battery after starting the engine and they'll run just fine. Alternator-equipped cars won't. :)

[vltjr]

Thanks Jerry. I'll have to wait untill the morning to have the battery load tested. In the mean time, is there any way to determine whether the alternator output is correct? Thanks again.

[Jerry Bransford]

Thanks Jerry. I'll have to wait untill the morning to have the battery load tested. In the mean time, is there any way to determine whether the alternator output is correct? Thanks again.

An alternator typically puts out 14.6 volts when it's charging but if your battery is bad, like if it has dead cells, that can make it impossible for the alternator to put out its full voltage. I'd wait to see what the results are from load testing the battery and installing a known-good fully charged battery. :)

[vltjr]

Well, I had the battery load tested today and it seems it checks out OK. I'm not sure how to proceed from here, such as how to test the alternator or voltage regulator. Any suggestions (preferably specific instructions/directions) will be greatly appreciated. ThaNKS.

[Jerry Bransford]

I'm a gearhead but I haven't had a need to get into either of my two Lexuses to know if the alternator is separate from the voltage regulator. Or, if it is the same as most modern alternators, the VR is built into the alternator. If the voltage regulator is part of the alternator as it likely is, you can just remove the alternator and take it into nearly any auto parts store and they'll test it for free. If you don't feel like pulling the alternator yourself, Pep Boys can test it for you in the vehicle. If you have an accurate volt meter, see if the alternator is putting out somewhere close to 14.6 volts (measure that voltage from the battery's + post) with the engine RPMs brought up to maybe 1500 RPMs or so. :)

[vltjr]

I think I'm going to go with measuring the alternator output in-vehicle with a meter, while running the thing at your suggested 1500 RPMs. I'll post the results. By the way, while the voltage regulator is located in the body of the alternator, it is separately removable and replaceable. That's the reason for my persistence in asking about a testing procedure for that component. Am I correct in assuming that if there is some measurable output from the alternator, and that output is increased/decreased when the RPMs are increased/decresed that the voltage regulator is faulty?

Thanks again for all your help (and patience) Jerry.

[Jerry Bransford]

I think I'm going to go with measuring the alternator output in-vehicle with a meter, while running the thing at your suggested 1500 RPMs. I'll post the results. By the way, while the voltage regulator is located in the body of the alternator, it is separately removable and replaceable. That's the reason for my persistence in asking about a testing procedure for that component. Am I correct in assuming that if there is some measurable output from the alternator, and that output is increased/decreased when the RPMs are increased/decresed that the voltage regulator is faulty?

Thanks again for all your help (and patience) Jerry.

The VR's job is really to monitor the battery's voltage and adjust the output of the alternator accordingly. So the alternator's voltage output will vary inversely with the battery's voltage... i.e. when the battery's voltage drops, the alternator's voltage output will raise. So the alternator's voltage won't necessarily stay steady as both the engine RPMs and battery voltage will affect it. At low engine RPMs, an alternator often won't put out enough to keep the battery charged. Don't try measuring the alternator's output without the battery being connected as doing so might damage it. :)

[vltjr]

At least I do know about the danger of running the thing without the battery connected. Thanks for the info, and I'll keep you posted as to the results.

[mejojo]

At least I do know about the danger of running the thing without the battery connected. Thanks for the info, and I'll keep you posted as to the results.

This is exactly what's going on with my 92 LS400 with 200k+ miles. Shop says alternator will put out when cold, but not when it warms up.

Other reading on this forum has led me to believe the alternator is worn out.

My plan is to take it out and put it on the tester at AutoZone and see what the machine says, taking care to run it for a while.

Anxiously awaiting any news from your end.

Joe

[vltjr]

OK--with a freshly charged battery (which read 12.75v) I started the car and measured the voltage at the battery terminals at various RPMs. My meter showed 11.9v pretty much constantly. Unless I hear otherwise, I'm assuming it's time to price an alternator. Can anyone steer me to a reasonably priced (but also reliable) rebuild? I'm also in need of instruction on how to do the removal/replacement. Last year I had to remove and repair the PS pump and high-pressure hose, and I recall it being quite a chore getting a wrench into that area. Any hints?

Thanks.

[SKperformance]

At what RPM did you check the voltage? under 800 rpms =12vdc any less and it is bad

Was the car at operating or starting temperature? if cold and it is not in the 13vdc range it is bad.

[mehullica]

I agree with SK. The alternator is bad. I'd stay with a DENSO, other brands are not as well built.

[vltjr]

Car was cold when I tested it. The RPMs ranged from 800-1500 and the reading stayed constant at 11.9v.

[Jerry Bransford]

Car was cold when I tested it. The RPMs ranged from 800-1500 and the reading stayed constant at 11.9v.

Well that sure makes the alternator diagnosis pretty solid. Yeah a brand like Denso would be good, avoid like the plague those "lifetime warranty" pieces of junk sold by autoparts stores like Autozone or Kragens.

OR, have it repaired by an alternator specialty shop which is what I'd try to do. That way you'll retain your OE alternator and just have whatever is bad, like a rectifier, replaced. They'll rebuild it to where it's like new too. You should be able to find an alternator specialty repair shop in your Yellow Pages without too much effort.

[landar]

At 1500 RPM, your voltage should be around 13.5 vdc +/-, so it appears as though your alternator is indeed bad.

I would back Jerry on staying away from the el-cheapo's at Autozone and the like. The lifetime warranty isnt

worth the paper its written upon. I second the advice of getting a Denso or having your existing unit rebuilt.

Below is a link to a tutorial on replacement. Not sure if it is for your year but you can take a look. Might be of help.

It cautions of a leaky power steering pump leaking onto and ruining alternators (the pump is above the alternator).

http://www.lextreme.com/alternator.html

[vltjr]

I always like having original parts rebuilt when possible. Does anyone have an idea what it costs to have this done? Jerry? The best price I've found for a Denso rebuild (from someone I trust) is $186+$40 core charge with free shipping (except for the core return, which I haven't yet determined). If a local rebuild is competitive, I'd prefer to go that route. Thanks.

[mejojo]

Car was cold when I tested it. The RPMs ranged from 800-1500 and the reading stayed constant at 11.9v.

Well that sure makes the alternator diagnosis pretty solid. Yeah a brand like Denso would be good, avoid like the plague those "lifetime warranty" pieces of junk sold by autoparts stores like Autozone or Kragens.

OR, have it repaired by an alternator specialty shop which is what I'd try to do. That way you'll retain your OE alternator and just have whatever is bad, like a rectifier, replaced. They'll rebuild it to where it's like new too. You should be able to find an alternator specialty repair shop in your Yellow Pages without too much effort.

I think I'm going to go with an eBay rebuild...$90 + shipping ($15-$30 depending whose shop) and some will give you a core refund if you send your old one in.

Joe

[vltjr]

I checked out Ebay after reading mejojo's post and found some rebuilt Denso alternators in the $80-$90 range and was wondering if anyone here has any experience with any of the sellers.

[Jerry Bransford]

I buy quite a bit of stuff on eBay but I'd still rather find a local alternator rebuilder. That way you have a local guy to talk to to get an idea as to the quality of his work and his warranty. Plus if anything goes wrong, it's local, no extra UPS delays. You bought a Lexus, a little extra $$$ for local faster service shouldn't be made an issue. :)

[landar]

vltjr,

I would think that in Austin, a local rebuilder would be easy to find. Personally, I would be leery of Ehay.

Also, check out this link..... just interesting info:

http://us.lexusownersclub.com/forums/index...amp;#entry49350

[mejojo]

vltjr,

I would think that in Austin, a local rebuilder would be easy to find. Personally, I would be leery of Ehay.

Also, check out this link..... just interesting info:

http://us.lexusownersclub.com/forums/index...amp;#entry49350

Why leery of eBay? They are just rebuild shops that are marketing there to hit a larger audience than your local shop. It happens that I live close to several of them (Los Angeles area) and their feedback ratings are excellent. If they were putting out bum product, it would be apparent.

Rebuilding an alternator isn't rocket science...you could probably do it yourself given the parts, tools, test eqpt. and a page of instructions.

Joe

[landar]

Why leery of eBay? They are just rebuild shops that are marketing there to hit a larger audience than your local shop. It happens that I live close to several of them (Los Angeles area) and their feedback ratings are excellent. If they were putting out bum product, it would be apparent.

Rebuilding an alternator isn't rocket science...you could probably do it yourself given the parts, tools, test eqpt. and a page of instructions.

Joe

Been burned before, Joe. Just a personal opinion, that's all.

[glenmore]

I just did this on my 1990 LS400, 155m. The battery discharge light was on, even after I put in a fresh battery. I bought a rebulit from a seller on ebay that happened to be local to me, only $55 with core. It fit fine except for the heat shield. On the original alternator it was attached with IIRC 4 screws but on the rebuilt one, there was only 1 or 2 screws. The body of the alternator was not tapped for the other screws. If you do send it to this Southern California ebay seller, keep your heat shield and screws. Replacement pretty straight forward. It is a bit tiring as it is heavy and you are trying to shot put it with the one hand and secure it with the other hand. In another thread, I had questioned whether this was the type of alternator problem that could be solved by just plugging in a new voltage regulator (like on my 1991 MBZ) but another member posted that his brushes were fine and the problem was where the brushes contact which apparently is very soft.

glenmore

1990 LS400

1991 300CE

2000 C280

[vltjr]

Sorry I haven't posted since I decided to order a rebuilt Denso from an Ebay rebuilder (not surprisingly located in Southern Cal.). I ordered it on Tuesday and it arrived yesterday. I installed it today and so far, so good. It cost me $110 total, and the seller assures that he will warrant it for 12 months. I too was a bit leary of placing an order from a shop so distant from me, but after comparing prices both for an already rebuilt one, or having mine rebuilt, I decided to take the chance. I'll post further regarding my experience (positive or negative) after putting some mileage on it and retesting.

Thanks for everyone's input.