93 LS400 A341E SPD pulses per mile?

[GSMnow]

I am finally getting close to firing up my 1UZFE Celica swap and I have a couple questions. I posted this a few days ago, but I see the forum must have crapped as all my posts including pics of the swap have been lost, so I am re asking my questions and should get the pics re-sent soon. I will down rez them this time as 4 mega pixel is a bit big;-)

Anyway, I need to create the SPD1 signal to the ECU from the SPD2 sensor in the trans. I know it will run with just one, but I can't have ANY error code in California, so I need ot get this right. Does anyone know the pulses per mile of both signals, or the ratio between them, like are they 4 SPD1 pulses for every SPD2 pulse?? The dash of the LS-400 had the circuit in it, but I don't have the dash to test it. Also knowing the pulses per mile from the Lexus will help me calibrate my own speedo so I know how fast I am going. They need to drive on a dyno at specific speeds to get it through the emissions test. Thanks in advance.

Gary M.
1UZA65C Celica Coupe 4.0 V8

 

[GSMnow]

Still no response, Hmm.

I picked up a few pats from the junkyard to try and get going on this, but I had no luck finding ANY late model Lexus for testing. I did pickup a 1983 Celica dash to experiment with and after I took it apart, I finally found the numbers printed on the face. 1026 revolutions of the speedo cable = 1 mile of travel. I tested my motor drive and it only take 3.5 volts to the motor to spin it past 130 mph. The reed switch on the speedo head produces 4 pulses per cable revolution. This works out to 4104 pulses per mile to the cruise control. Now if I could just find out the actual pulses per mile from the Lexus A341E trans.

Gary M.

 

[Peewee]

Assuming the LS400 A341E is the same as the SC400 A341E, then;

SP2 gives you 4 pulses per rev of the output (drive) shaft
SP1 or SPD gives you 4 pulses per rev of the speedo gear.

Speedo gear is usually turning at 1/3 (6/18,6/19 or 6/20) the speed of the output shaft.


I am assuming you are keeping the RA65 dash and RA65 speedo cable?
If so, the output from the RA65 dash to things like the cruise control ecu is 4 pulse per rev, and this can take the place of SPD quite nicely.

 

[GSMnow]

Sorry this post gets long, but I am thinking to myself while I type as it helps me catch errors in my math.

Thanks for the reply. I would also assume the LS and SC cars from similar years would be the same. So SP2 is 4 pulse per rev of drive shaft. If SP2 is in fact a 3:1 ratio off of the shaft it then comes out to 3827 pulses per mile.

With my smaller tires and 3.727 rear end, these will obviously be higher frequencies, but as long as they are the right ratio off of the engine speed and to each other, the trans should shift at the correct engine RPMs. Now to get my speedo to read right.

Doing a little math, knowing I need 1026 revolutions of the speedo cable per mile, (this produces 4104 pulses per mile at my reed switch) I think I can get pretty close doing this in integer math.

At 4 pulses per drive shaft revolution would get 11482 SPD pulses in one mile on the Lexus but with my street tires that are probably going to be 215 60 14's and my 3.727 rear gear I will get a higher 12821.82 pulses per mile. (My Hoosier race tires are even shorter and I have 205 55 14 tires also)

So for the Odo (and speedo) to be accurate, every 12822 pulses from the trans I need to turn the speedo head 1026 times to see 4104 pulses from the read switch.

12821.82/4104 = 3.124

8 to 25 works pretty good. Even rounding to all integers would be less than 1/2 % error. This would be easy to gear, if I had a cable at all. But using a DC motor control I could to it in math and adjust the motor speed to hold the ratio. I don't like the idea of having to do the servio control so..

My other plan is to try driving a stepper motor from the SP2 pulses. I need 96 pulses to turn the speedo 1 revolution. This means the stepper needs 96 x 1026 pulses per mile. That is 98496 pulses! Wow! 7.682 pulses for every SP2 pulse. To get close I need to go up to 22:169 Those both fit into 8 bits so it might work. I will need to do the divide first, but that could loose accuracy at higher speeds when the count numbers get low.

The main timer in HC11 has several possible dividers. I like using a divide by 4 which counts 500,000 times per second. At 60 MPH I will be getting an SP2 pulse about every .00468 seconds. This results in a count of 2339 or 2340 counts depending on if it rolls the fraction or not. Dividing 2340 by 169 will give a result of just 13 which is getting pretty low and could have a fair sized error eve if it is just 1 count off. Multiplying it by 22 then gives a count of 286 (integer rounding all steps) for each pulse out. Using the 2339 also results in a 286. That count at 500,000 counts per second comes to a pulse out of the HC11 at 104895 per minute. This turns the speedo at 1092 rpm. That is 6% fast. Or 60 mph actual shows as 64 on the speedo. I think this can be closer if I move around the numbers, or split up the math different. I got the stepper motor to run to over 90 mph with a pulse generator, but I didn't have it turning the speedo head. I will try that tonight.

Gary M.

Putting an AutoMeter speedo in is looking better and better.

 

[Peewee]

Umm, whoa, dude, wtf??

I didn't even bother reading that because none of it is necessary.

But whats wrong with using the stock LS400 SP2 going to the stock LS400 ECU, and the stock RA65 speedo cable going from the tranny to the stock RA65 dash, and the stock RA65 dash SPD output going to the stock LS400 ECU?

Thats how it is in my car and it works perfectly.

 

[Peewee]

Wait, you can't connect your stock speedo cable up can you?

It would be much easier and nicer to adapt the speedo cable to the tranny.

Use an MX83 rear tranny housing and convert the tranny to a standard slip yoke.
At least thats what I would have done, but I do realise you have already had a driveshaft made up.

 

[GSMnow]

How much of the trans needs to be swapped out to change to a slip yoke? When I asked about that a coupole months ago, it sounded like I would need to tear it down quite a bit to change the output shaft of the trans as well as the rear housing. And the slip yoke rear housing would not have the matching sensor positions in it? If it is just a housing swap it would not be that tough. I did find a couple A340E cars at the junk yard, and they did have slip yokes, so I could get the parts, but it looks like a huge job. Programming a microcontroller is something I can do whil.e I am at work during slow hours, which we do get. I have a DC brush motor mounted on the back of the RA-65 gauge setup that I bought and I can adjust it speed to show from 5MPH to over 130MPH with a PWM signal. I greatly simplified the math since the stepper motor just won't go fast enough under load anyways. I settled on 3 ratios for 23 24.5 or 26 inch dia. tires. I need to get the Lexus book from Chicago again though. It looks like the SP2 from the sensor in the trans went to a divider in the speedo on one sheet, but on another it shows it just making the wave a clean square for the ECU, but still being the same pulses per mile. Either one is easy in the microcontroller. The hardest part is that it will have to adjust the PWM to the motor all the time to keep the motor speed at the right ratio from the SPD rate. It is plenty fast to make a correction every rotation of the speedo motor, the tricky part is making it corret fast enough to not lag behind changes, and smooth enough to not over shoot up and down while it hunts to follow the input speed. Sorry, more thinking while typing.

I also looked for an MA65 digital dash, as that would just need the right pulse rate. No luck finding one yet, and I still think the Odo used the cable.

Gary M.

 

[Peewee]

Yeah, the MA61 digital dash still needs the cable to turn the odometer.

You could do what I've done and put in an SC400 instrument dash, but then the fuel gauge will need trickery to work.

As for swapping the rear to a slipyoke, have a read of this thread
http://thermactor.com/forum/viewtopic.php?t=8049
The guy there, MacroP has done just that.
He found a walkthrough on the web for it, but when he did it the 2nd time, he found that the walkthrough did many things that were not necessary.

 

[GSMnow]

Peewee,
With a little careful fitting, my friend got the Lexus rubber drive to fit, check out the pics on my Progress thread. The Lexus drive shaft actually fit inside of the original Celica shaft. It is a nice snug fit and runs true, so he welded it up and it will make the car drive until I can have a one piece shaft made up to get rid of the center bearing.

As far as the speedo drive goes, I found a small stepper motor that makes plenty of torque with a microstepping driver that it pushes the speedo to over 130 mph against the pin. The only tough part is that I need about 13 step pulses to the driver for every pulse from the SP2 sensor if the trans. I have a program in a small microcontroller coming together, and it should work fine. It seems my 93 trans actually does have a sensor in it for the SPD and SP2 signals, so I will feed the SPD to the cruise control directly, and buffer it to the ECU since I don't have the Lexus speedo buffer. The book shows it as 4 pulse per driven gear rev with no divider, so that is easy, just shape the reluctor signal to a 5 volt square wave. I looked into the JayCar speedo adjuster mentioned in another thread, but it can only double the pulse rate. I would need 4 of them in a row. My HC11 can do any multiple failry easy.

I really hope to have my beast on the road before summer is over.

Gary M.