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Old 06-01-14, 03:23 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, 07:02 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, 07:13 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, 07:29 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 06-01-14, 11:41 PM   #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 06-01-14, 11:45 PM   #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, 12:09 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, 02:01 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, 04:02 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, 06:51 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, 08:57 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 02-01-16, 01:15 PM   #12
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I've got similar problems on my '91, whose dash has never been opened.

Summary of issues:

Tach needle
- at first this would happen in the cold - it would stick at certain values, like 0, 800, 1000, etc. - this seemed to be a mechanical issue, that something was mechanically stopping the needle from moving, but once it moved it would be OK. I can believe that a weakened needle motor will cause this problem.

- recently this seems to be a permanent problem. Tach reads fine at idle. When driving easily around town, it seems to stick at 1000, even when I hear the engine rev'ing higher. When flooring it (to take it to 6000), the tach goes to 3000 and sticks, even while I hear the engine pulling to 6k.

Speedometer
- this seems to be partially an offset (it reads below zero when the car is stopped) and partially a scale factor error (reads up to 20% lower than it should, proportional to increasing speed; this error is separate from the fixed offset). It does NOT stick - it always moves, just that it starts negative and does not increase enough.

I'm looking for ways to troubleshoot and fix this problem. I know I could send the instrument cluster out to be repaired, but do not want to do that. I replaced all my ECU capacitors a couple of years ago, using the exact ones specified on this list. (BTW, that fixed a few minor problems that I did not even know I had)


From reading on the list, I've found:
Tach signal - comes from crank position sensor ==> ECU ==> igniter #1 ==> engine compartment diagnostics port ==> gauge cluster tach.

Is that right?

I assume the signal is still pulses at the diagnostics port, so I'd need to count those, right? My guess is that it will be with the cluster, since the actual running of the car is fine. So I expect if I count pulses there, they will be right, and if they are, I will have isolated the problem to the cluster in one step.

Speedo - possible problems are a slipped needle causing the offset, and a weakened needle motor which causes the scale factor loss.

I would investigate the cluster problems by removing it and mechanically and electrically inspecting and testing the motors and needles.

It does not sound like I have any cold solder joints, but I'll certainly look for those and won't hesitate to resolder any joints in there.

Any corrections, additions, or other advice (like troubleshooting suggestions, likely root causes, replacement part sources, ...)?
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Old 02-01-16, 01:27 PM   #13
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So from above then if the engine is running, a tachometer not reading correctly would be the cluster then.
Tanin says he can fix it. Tanin is the best bang for the buck, the cluster is not fun to work on.
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Old 02-02-16, 05:29 AM   #14
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Quote:
Originally Posted by dicer View Post
So from above then if the engine is running, a tachometer not reading correctly would be the cluster then.
Tanin says he can fix it. Tanin is the best bang for the buck, the cluster is not fun to work on.
Thanks for the mention! We are always happy to help and will always take extra good care of our Forum friends. Just call us and mention that you talked with us on the forum and we will do whatever we can to also expedite service if possible, since we know how hard it is to be without your car for too long!

Here is the link to the LS400 cluster repair service:

http://www.taninautoelectronix.com/L...ter_repair.htm

Call us for more information on pricing and time frames. We are here M-F 9-5 CST.

Thanks,
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Old 02-02-16, 07:40 AM   #15
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As dicer mentioned, Tanin is a very good repair service for these clusters. If it is the needle motor/assembly that is bad and the needle does not rest below the "0" marker, the fix I wrote about below may not work for you.

I had this problem with my tachometer, where it would read 20-40% lower as the RPMs went up. It looked very similar to this cluster; however, that is a picture from another LS400. [It happens over time with these cars] I found this fix on the Lexus Owners Club website, which worked perfectly for me. Here is the text from that post:

Quote:
Originally Posted by ramnozack
okay guys, I am going to give you a very constructive advice on how to fix this problem.
  1. First remove the cluster and if you do not know how go to lexls.com and follow the instructions.
  2. then remove the face cover .first grap the tach needle gently and pull untill you hear a pop,again be gentle and do not ge scared.
  3. once you hear the pop move the needle clockwise untill it pops again then gently release it.
  4. now move the needle slowly counterclock till you sit it over the zero an on the dot and make sure that it sits right on the zero.
  5. to check your work move it gently say to the mark 3 then let go it should snap right back to zero,once you have accomplished this ,you are rock & roll baby. the same thing goes for speedometer.
... this job should take about an hour if you how to handle things. Good luck and let me know.
please make a donation to lexls.com, this guy is great.may god bless his soul.
Here is ramnozack's profile, to cite a source.

Last edited by CELSI0R; 04-09-16 at 09:42 PM.
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