lexmoose

After searching a lot on this and other Lexus related site I found that many with 2LS (and other Lexus) have issue with their charging system at idle.

In my case I have a 96 with 90k miles on the clock. Now When I purchased the car back in July the mechanic who inspected the car found no issue except for the battery that was at around 60% (rebuilt). Never really noticed the problem before fall since my I'm using my bike to go to work and never really got stuck in traffic with many accessories on.

Anyways, after a month at the body shop I get my car back early November, the guy need to boost the car since it sat there for a week and there was a bulb turn on in the back... Go home and decide to let the car run for a few minutes to let it charge a bit, headlight are set to auto with fog and when I got back my scangauge (obd2 reader) indicate that the voltage is under 13V, turn on the rear defrost and seats heater and the car was down to 12V or a bit under (can't recall). Go the the part store and get a brand new AGM batt, go back home install the new batt and let the charger on the car overnight.

Next day, go for a ride, park and turn on all accessories, voltage goes under 12V, decide to leave it as is since I plan on getting an HO alt in the spring for my SQ install. But the other day, I was stuck in traffic, big snow/ice storm, so defrost is running, wipers, fan set to max... Voltage drop under 12V and the fan slow down, after a few minutes I can barely see outside. Turn off the headlight/fog, rear heater and try to keep the RPM higher, voltage come back after 2 minutes (regulator reset from protect?) and the fan is spinning faster and I can start to see again.

I decided I needed a new alt now.

Enough bla bla here's what I've done so far.

• Have the non-factory alt in place rebuilt using same regulator (no stock)
• Replace the belt
• Change the regulator on the same rebuilt alt, it's now a 100A alt
• Replace the rebuilt alt with a new Denso 80A
• Inspect all connection
• Test with a DMM if there was any resistance causing voltage drop (at batt terminals, alt wire, alt fuse)
• Made a temporary ground from batt neg terminal to block
• Inspected the harmonic balancer to see if it was slipping
• Unhook the alternator to have the car run only on battery so I can measure the load (66A@12.1V with headlight, fog, rear defrost and both seat heater)

With that latest test I discover 2 things, first there's no way the 80A alt will produce 800w at idle and second the battery light came on. What's weird is that the batt light never came on with the alt plugged even if voltage was going down to 12V...

Now I see 2 possible cause

1. Lexus engineer under estimated the power needs of the 2LS at idle and they tweaked the ECU to not display the batt warning light if the alt was just maxed out
2. The 800w load i'm seeing is not normal and there's something else happening here.

If it's the first one, many of the 2LS owner driving in winter must have this issue and I'm curious to know if that's the case. Many probably don't even notice it since they don't have a voltage reading in their cars.

Any 2LS owners willing to do some tests? It's simple let the car heat up until it idle at 650RPM, then turn on the headlight, fog, rear defrost, seat heater (if they work) and set the fan to the maximum speed. Measure the voltage, ideally with a DMM at the battery.

Thanks

EDIT: possible I forgot some details, worked for 24h in a row...

fixmiester

We seem to be seeing more and more stories like this lately. I recently replaced my original alt. because of two bad diodes (looked at it with my scope, to confirm), it had become noisy, and the symptoms were very similar to yours. Put in my brand new after market alt. that came with a QC test sheet showing voltage and current under load conditions for this unit. Started it up and confirmed charging levels at various RPM and load conditions. However, at idle under heavy load, the charging voltage fell to 12.5 volts, but came up to 13.75 at 1200 RPM, rising to over 14v. under light load . Put my scope on it to make sure I had all six pulses, and there were.

I'm convinced that the original 80 /100 amp alt. is simply marginal for heavier loads @idle. It will keep the battery charged, but barely. Otherwise, it works okay. At driving speed it's good. If you are adding additional loads, do an upgrade.

randal

I have seen this too and measured the voltage with various loads on. With all heavy loads (heated seats, defroster, brake lights, headlights), the alt will not keep up with the demand at idle. Move about idle (1200-1500 rpm) and all is good. I remember reading in a manual and it stated that if you are stuck in traffic, turn off some of the accessories to keep from discharging the battery. But in most driving conditions, you are not at idle very long so it is not a problem.

This is not peculiar to Lexus. I have seen it happen on other cars too. Nothing wrong with it per se'. Just a design tradeoff at what rpm the alt will produce most of its power.

timmy0tool

iTrader: (7)

of course you will see a strain in voltage with all the accessories on at idle in the cold! it's the perfect storm. you can have others measure the voltage but there are so many factors involved that results will vary.

best to get a higher output alt now, since it sounds like you will be needing it in the future anyway for your new sound system.

Yamae

You will know more seeing the chart below although it's from a Denso's 130A generator. The top horizontal scale is 200A. Due to the pulley's diameter the rpm is higher than the engine's.

randal

It has nothing to do with the cold other than you are more likely to be using more current hungry accessories(seats, defroster, mirrors) in the cold than in hot weather. The Alt is actually slightly "happier" (runs efficiently) in the colder weather.

Shmee

iTrader: (3)

An alternator is not meant to charge a dead or low battery, it is meant to maintain a charge while running with a load.
AGM batteries are not a good choice in cars because if they do go dead, jumping them can often kill the battery and trying to charge them with an alternator from dead can also have the same sort of results.
You need a special battery charger with an AGM battery or you will kill them.


My suggestion would be to get a good deep cycle battery and in the in-term you could cheat and just get a smaller alternator pulley.

lexmoose

I just want to make sure if others like me are in this situation they get a clear answer from this thread. So no, the factory alternator is not powerful enough for the car basics needs at idle.

Got many other cars (cheaper made) over the years and never got that issue.

Got an email from Mechman tonight stating that their 240A alt will produce 140A cold and 100A hot at idle for our car. We are also waiting for an answer from the local alt rebuilder to see if he can upgrade the factory one to get 80 to 100A at idle.

Shmee

iTrader: (3)

Something you have to consider is the clientele these cars were engineered for when new. I'd go so far as to say that 100% of the original buyers of this car owned a garage and probably worked in a large office building or a place with parking away rom the elements. The need to have the heater/AC, rear defrost, wipers, fogs, headlights, seat heaters and stereo up full blast the moment they got in the car is not what the probable 90% of the current owners now face. While i agree an 80Amp alternator is a joke, pretty sure my old $15,000 NEW ford focus had 120A alternator from the factory; when taking into account the original engineering and customer base, 80A is actually probably very sufficient. This is why, from what I have notice at least, most of the continuous alternator problems happen in colder climates and the folks in Cali and the souther states tend not to report similar issues.

That is also the reason why I opted to get the 320A Mechmann alternator, over the 240A, as mine puts out 167A at idle. Which is more than capable of handling all the accessories plus my upgraded stereo and air compressors and anything else i want to throw at it. I will never NEED 320Amps, but the output at idle and lower revs is what I was after.

lexmoose

Well headlights, fog and rear defrost(side mirror too) is not uncommon up north and those people were also getting stuck in traffic back then.

Mine will idle at 650 hot and can dip just under 600 when in drive (stopped). After talking to Mechman they told me their 320A wouldn't kick in before 750-800, but their 240A will be fine. Did you adjust your idle?

lexmoose

Ok local rebuild shop built a 140A, but would still not provide enough power for some factory accessories at idle.

So I spoke again with Mechman and they also have a 170A version of their S serie for our car (not advertise on their site) for 299$

here's the spec

170 amp 6 phase alternator with 12 press fit diodes, twin rectifier plates and use hairpin stator

300 rpm turn on
500 rpm - 120 amps
800 rpm - 150 amp
1600 rpm - 170 amps

Ordered mine today, so expect an update in a 2-3 weeks

For comparison here are the spec provided by them for their other S serie

240 amp
500 rpm turn on
650 rpm - 100 amps
800 rpm - 140 amps
1800 rpm - 240 amps

320 amp
600 rpm turn on
700 rpm - 100 amps
850 rpm - 140 amps
2000 rpm - 320 amps

Shmee

iTrader: (3)

That actually sounds like a pretty decent alternator for 95% of the community, even as an OEM replacement.

Midengtoy

iTrader: (3)

I have had the same problem. When we had a winter storm in MN and I was stuck in traffic for 2 hours everytime I stepped on the brakes and battery light would come on. I thought maybe my car was idling too low so I had my foot on the gas and brake at the same time to increase the revs. I had to shut off the radio, fog, and defrost in order to avoid the battery light to come on. After I figured that out I thought maybe the alternator was bad but the previous owner just had the alternator replaced along with the serp. belt. I haven't had this problem since then though because I haven't been stuck in traffic that bad again. I have a 1997 LS400.

Shmee

iTrader: (3)

I really hope you shifted it into Neutral or Park when you were doing that otherwise you put a prett decent load on the transmission and could quickly burn out your fluid and and transmission as a result.

Midengtoy

iTrader: (3)

I only did it the brake/gas thing 3 times before I figured out shutting things off helped. Also I wasn't doing a trans brake launch type of thing just increasing the revs up to 1k rpm and that was enough for the light to go away. The issue hasn't come back since then.