Down-shifting 1991 Lexus - A Second Try For Feedback

[sudhir]

1991 Lexus LS 400 with 127k miles. Here's my problem - the car is fine when I drive during the day. But when I turn on the lights at night, for some reason it down-shifts - I can feel it do so, and the tachometer shoots up (really high, to about 6000 rpm, close to the red line, when I drive at say 70mph on interstate), and I can hear this whirring sound from the engine. Any idea what's causing this? If its an alternator problem is it going to be expensive to fix? what am i looking at in terms of bucks? thanks!

[dcfish]

1991 Lexus LS 400 with 127k miles. Here's my problem - the car is fine when I drive during the day. But when I turn on the lights at night, for some reason it down-shifts - I can feel it do so, and the tachometer shoots up (really high, to about 6000 rpm, close to the red line, when I drive at say 70mph on interstate), and I can hear this whirring sound from the engine. Any idea what's causing this? If its an alternator problem is it going to be expensive to fix? what am i looking at in terms of bucks? thanks!

This is not a joke, There is a wire in the trunk hinge that is shorting out. The insulation may be worn through. Lexus made this wire too short and causes all sorts of strange problems in the early ls400's. Search these forums and there is plenty of info on this subject.

[eatingupblacktop]

Like dc says the wiring in the trunk is likely your problem. It was for me with similar symtoms.

It's an easy fix. Here's a link I got from Leadfoot:

http://us.lexusownersclub.com/forums/index...+wiring+harness

[qha_vn]

it wont cost you much money but time to find the cause of trouble

since tranny control wires are under shifter deck, i think it should be the first place for you to find the shorted wire. to me its likely that the OD wire (down from shifter to under deck) may be shorted with the shift illumination (so you can see P-R-N-2-L at night when lights are turned on). you can try pressing OD while doing 70mph during day time to see if the car does the same as when you turn lights on at night. if its similar, most likely OD wire is shorted

once knowing the cause, open the shifter deck trim is quite easy, simply pry it off using a screwdriver at the right end if you sit on driver seat. you may aslo need to remove the shifter to completely remove the trim. Remove it and make sure all the wires under are properly sealed

[fiveofakind]

eatingupblacktop...your link doesnt work.....

[90LS400Lexus]

I never had that harness problem on my old 1990 LS400. I had wondered if my current 1991 LS400 had ever had the issue or not, so I posted a photo of it here or on another Lexus site. I was told that it looked like it had been repaired before.... Here is a photo of my harness near that trunk hinge. I guess if it looks different from this, then it has not been repaired and is likely the problem. What amazes me is that Lexus never issued a recall on this widespread issue. It also amazes me that no fires have been reported from these supposed shorting wires... no fires that I know of anyway.

[eatingupblacktop]

eatingupblacktop...your link doesnt work.....

Sorry about that. Try this, I just tested it & it works:

http://us.lexusownersclub.com/forums/index...+wiring+harness

[eatingupblacktop]

I never had that harness problem on my old 1990 LS400. I had wondered if my current 1991 LS400 had ever had the issue or not, so I posted a photo of it here or on another Lexus site. I was told that it looked like it had been repaired before.... Here is a photo of my harness near that trunk hinge. I guess if it looks different from this, then it has not been repaired and is likely the problem. What amazes me is that Lexus never issued a recall on this widespread issue. It also amazes me that no fires have been reported from these supposed shorting wires... no fires that I know of anyway.

The tape job on yours looks a bit messy but It looks like you have extra slack which is good. When I repaired mine, I just spiced one wire. This summer I think I'm going to redo the whole bundle giving the extra slack Lexus should have provided for in the first place. I think a coiled assembly would have been a much more elegant solution. If it's not a case of the bean counters getting control over some of the production, then I hate to think it's part of a "make work" program. Lexus wouldn't do that would they? :whistles:

[90LS400Lexus]

Yeah, thats what I thought too, but it was like this when I bought it. No issues, so I can live with the messy tape. So basically if no slack there on a LS400, then it has likely not been fixed yet? I was unsure of exactly what the issue was. I see now. I guess when the trunk opened that it stretched the wires too much? I do not think my old LS400 had even been repaired, but I had not had any issues at the time either.

I think the tape is "messy" on mine because here in the south it gets very hot and I think that tape looses its grip so to speak. Thats what looks like happened to me anyway.

The tape job on yours looks a bit messy but It looks like you have extra slack which is good. When I repaired mine, I just spiced one wire. This summer I think I'm going to redo the whole bundle giving the extra slack Lexus should have provided for in the first place. I think a coiled assembly would have been a much more elegant solution. If it's not a case of the bean counters getting control over some of the production, then I hate to think it's part of a "make work" program. Lexus wouldn't do that would they?:whistles: