1991 LS400 manual swapped speedo help.

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louishavenhand

New Member
Messages
3
Location
Sheffield
Hi All,

Decided to join for some help on my project i've just finished (6 speed toyota J160 unit into a UK 1991 Lexus LS400).

Swapped the auto transmission for a manual toyota J160 6 speed unit. Ive done all the work myself which i'm dead chuffed with (custom pedal, handbrake on the tunnel done nicely, custom trans mount etc). The only job left it to try and get the speed sensor working properly.

I have re-pinned speed sensor 1 on the auto box to work (3 pin OEM plug with power, signal and earth).

Though now it technically "works" the early Ls400s used a 20 pulse signal thats interpreted by the communication box into a 4 pulse signal before its fed to the ECU. The J160 is only a 4 pulse signal, so in real world terms when I am doing 50mph on the GPS for example the speedo tells me i am doing 10mph (20/5 = 4).

Is there a way to get this to work? Ive seen convertors online that say they will work up to certain percentages (from 5%-900% for example or up to a 400% increase depending on brand) but I am worried about spending a chunk without proof of concept. For example some units only providing a max output of 5 kHz when by my maths I need a 500% increase up to a max output of 30 kHz for it to work in the full range of the speedo (max revs in 6th gear for example), unless my math is way off?.

This Is getting very close to the end of my scope of ability (I'm an english teacher by trade). I'd really like a working OEM speedo in the car so any help is much appreciated. I saw an old w58 swap thread where a later set of clocks was used as they're different and rewired so i'm open to options that would work.

Thanks again,

Louis.
 

Zuffen

Super Moderator
Staff member
Messages
5,471
Location
Sydney, Australia
What you need is a frequency converter.

Whilst I haven't checked ebay may produce something from China, if you don't mind using their junk, but it may be an option to explore.

Electronics stores will sell a kit or complete item at a better price than what you find on car parts sites.
 

louishavenhand

New Member
Messages
3
Location
Sheffield
Hi mate, thanks for the quick reply!

Ive been looking at signal modifiers but what I'm worried about is the ability they'll have to modify the signal through out the whole speed range.

Im reluctant to fork out if it'll convert perfectly until a certain MPH based on the max kHz it can produce and then stop working? Unless Im on the wrong math/train of thought?

Cheers
 

George_R

Well-Known Member
Staff member
Messages
1,020
Location
Russia, Moscow
you don't need x5 frequency multiplication, although the device is capable of doing it
instead it's recommended to source front wheel abs sensor's signal which will give better accuracy (and it will require frequency division of about 1/10th which is also possible)
 
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