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Question for Yamae or someone who knows - 1990 ls400 speedo and tach low by 10-20%

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Old 06-01-14, 04:23 PM   #1
peterls
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Default Question for Yamae or someone who knows - 1990 ls400 speedo and tach low by 10-20%

If yamae is reading this it would be great to hear his opinion:

http://www.clublexus.com/forums/ls40...t-cluster.html

basically here you can see that people have replaced capacitors on 1990 ls but did not get any improvement on their speedo and tach (rpms) needle - they are still a little low, just like mine is. Basically, my rpms is always showing about 25-50% less than it should. My speedo needle is about the same - 25% or more slower than it should be. So if I am doing 80 mph ,it may be showing 60 mph.

So, if it is not the caps, what is it??? Resistors? Some failing CPU on the board? Or do you think it may be the speed sensor (I doubt that one it would probably throw many other things off)?

Others, please respond only if you know for sure what the answer is, and if it applies to 1990 LS. We have plenty of guesses and answers for 1993 and 1994, and those do not apply in this situation.
Thanks!
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Old 06-01-14, 08:02 PM   #2
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My speedo saying I am going faster than I am.
At 35-45 it reads 1-2 mph slow and at 65-75 it read 5 mph slow.
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Old 06-01-14, 08:13 PM   #3
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my 90 got the same issue, I have fixed it but not sure if applicable to yours. shut up for safety.
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Old 06-01-14, 08:29 PM   #4
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I have not analyzed the low indication issue for earlier models and I am sorry that I have no idea to answer your question.

This is just my guess but the low indication is caused by missing pulses too. So in order to fix the problem, you need to check and count the number of pulses. If the pulses from the ECU are already missing some, you can't fix it at the meter side. You need to fix the source side. Does you ECU have good capacitors?
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Old 06-02-14, 12:41 AM   #5
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Quote:
Originally Posted by qha_vn View Post
my 90 got the same issue, I have fixed it but not sure if applicable to yours. shut up for safety.
So how did you fix yours?
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Old 06-02-14, 12:45 AM   #6
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Quote:
Originally Posted by Yamae View Post
I have not analyzed the low indication issue for earlier models and I am sorry that I have no idea to answer your question.

This is just my guess but the low indication is caused by missing pulses too. So in order to fix the problem, you need to check and count the number of pulses. If the pulses from the ECU are already missing some, you can't fix it at the meter side. You need to fix the source side. Does you ECU have good capacitors?
Thanks Yamae,
How would I count the pulses, they must be too fast for me to see them with a naked eye, right?

As for my ECU, I have two, and they are identical and they both give me exactly the same driving performance and so on. I bought one as a backup, used, but very new, and neither had their caps replaced; they seem to be just fine. However, I plan on doing that eventually.
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Old 06-02-14, 01:09 AM   #7
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Quote:
Originally Posted by peterls View Post
So how did you fix yours?
I noticed that when my car stays, speedo needle falls below zero, this was the cause for real speed faster than indicated. I used my finger to adjust the needle pointing to zero. that was the fix.
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Old 06-02-14, 03:01 AM   #8
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In my case with the off speedo, in my 92 sc400 which is worse the colder it is! It must be an internal speedo problem since the odometer is getting the correct miles!

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Old 06-02-14, 05:02 PM   #9
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The problem is the needle motor/assembly. We replace these weekly in older LS models. Call us and we can repair any issues you have.
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Old 06-18-14, 07:51 PM   #10
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Can only speak for the Tach - the speedo is probably similar, but I cannot vouch for that; the tach needle mechanism (tail end of the needle behind the gauge face) has a stop block internally, but it can be lifted up and moved past that block. This may have happened if someone tinkered with the needle, or if the car experienced some kind of jolt. I checked this out when I changed my tach, by the way, so if you take the tach out of the dash cluster, it is possible to carefully lift the needle just that little bit and move it so it is back in position. I believe one of the previous posters meant that when he said that he adjusted the needle. Note however, that you will have to be pretty careful, since it is easy to mess up a number of things while doing this.
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Old 06-18-14, 09:57 PM   #11
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mine went out when I hit a huge pothole on highway 80 near redtop road when they were repaving it..my speedo just dropped..i had to use my gps for the speedometer for the rest of my trip
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Old 06-18-14, 09:57 PM
 
 
 
 
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