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Computer/electrical Problem


LS400Convert

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I have owned a 90' LS400 for about 2 years. It has been an awesome car, but now I am stumped. On a particularly hot day, I drove the car a few miles, shut it off, restarted after a few minutes and all warning lights remained on on the dash but the engine was running fine. As I was driving it became apparent that my dash lights were dimming and my fan on the air conditioner was running slow so I then thought I had lost the alternator and had been running on the battery. I normally would replace it myself but I didn't have the time. I called the Firestone place to come get my car and replace the alternator and serpentine belt. When they came to get it (I wasn't there) they said it started right up and they drove it to their shop. They didn't replace anything since they couldn't find anything wrong. When the car cools down completely it will start and run fine whether you drive it 1 mile or 100. But if I shut it off and then get back in and drive, then all the lights come on and I assume once again that I am running on battery power only. I put in a brand new battery a few days back and it didn't help. Could it be the computer? Thanks for any help you might offer.

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;) It is just a Thought, but you might have an overheating problem, make sure you keep an eye on the temp Gauge and see how high it gets. I also own a 1990 LS400, I recently flushed it's cooling system for the summer and replaced the thermostat. Some of this high tech cars tend to run bad and most of the times they shut off completelly when overheating. Again it is just a thought... ;)

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it is very possible to be the alternator

check to see if the power steering pump is leaking on to it which causes an occasional problem

also make sure the secondary battery connection after the terminas are secure

i don't think it is an overheating problem

as you would have the issue before shut down

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Are these the light's that come on in your instrument panel: low oil level, low coolent, battery, parking, tail light out: if these are the lights that are on then your alternator is bad, when the alternator gets hot enough then something in the regulator opens up. My did the same thing to me last week on the way back from california I trouble shoot it for about two hours in which time it cooled down enough for me to ge back to New Mexico, I was traveling at night. when I got home I found a wiring print from a friend of mine who is a mechanic. and all those lights are hooked up directly to the yellow wire coming from the alternator, and go thru several dioeds, so instead of just the battery discharging light coming on, all those lights come on. probably lexus's way of making you go to them and replace the alternator for big $$$. Mine cost $229 from Checker auto, they have on for $175 made by autolite but I don't think it has the pulley installed on it. should get it tomarrow, and today i'll get under in to pull it out. Try one other thing on it, this is when I first noticed it, press your gas pedal down to the full throttle button and see if you can make the lights blink off/on, also your cruise control won't work if all the light are on.

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Thats exactly what mine did. Including the blinking under heavy acceleration. Like you said, it has all the symptoms of alternator, but usually when I have had alternators go out on other cars, they just quit and thats it. This one has something that reacts to the heat.

Anyway, thanks and I will let everyone know if that fixes my problem.

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my es has a weird one also they alternator is crap at idle only 12 volts but jumps after 1200rpm

which is kind of normal but still doesn't give the right amperage

when hot

it is perfect when cold

even took it out and to a shop and they opened the whole thing to find a problem and said it works great

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Many Japanese cars use an alternator field disconnect switch at idle, which eliminates charging drag and improves idle quality. This may accound for the jump in output voltage as you rev the engine. I do not know if the Lexus line does this though.

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  • 2 weeks later...

If anyone reads this thread, I replaced power steering pump and alternator. The alternator fixed the problem, excellent diagnoses. Thanks for the help. It was about 5 hours labor and $450 in parts that I purchased at O'Reilly. First time I've ever done it on this car and hopefully the last!

:lol:

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glad the community helped you

also i found lexus has made a new sized pulley wheel for my es as to get more juice at idle

so i may gety a new wheel

but since a changed all the wiring from the battery to the engine i start and run much better than before

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glad i could help. the alternator took me about 2 hours to change, since i didn't put a new power steering pump in. I did build a shield to go over the alternator so any dripping oil will not get on the new alternator. Last week on the 4th of july my water pump let go on me so i'm in the process of replacing it and the timing belt. it's a pretty easy to do, just a bunch of sensors to remove without breaking any of them.

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  • 1 month later...

It's pretty nice over here right now, our high are 90-92 degrees and nights a 70-75, and getting rain in the evenings. as far as the neighborhood we're getting a lot of people moving in from california, and that group of people can screw up anything. it's a good thing we have a big mining company out here that owns a lot of property or they would try to fill up the hills out here with houses.

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glad i could help.  the alternator took me about 2 hours to change, since i didn't put a new power steering pump in.  I did build a shield to go over the alternator so any dripping oil will not get on the new alternator.  Last week on the 4th of july my water pump let go on me so i'm in the process of replacing it and the timing belt.  it's a pretty easy to do, just a bunch of sensors to remove without breaking any of them.

What did you build the shield out of? I was thinking of doing the same thing last week. Can you take a digital picture and post it here. I'm very interested.

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when you remove the alternator you have to remove the shield that is on it to put on the new one, just use that and a piece of sheet metal or aluminum. I made it like a tube just to make sure anything that dripped on it wouldn't get on the alternator. it's been on the car for a couple of month now and i'm not going to take it of to get a picture of it. I changed my oil last week and haven't seen any new leaks on it so i probably didn't need to make the sheild anyway.

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