Modifying SP2 Speed Sensor Output??

[Z2TT]

Hello,

I have a 4.3 Diff in my car .... the Engine I'm putting in my car came from a car that had a 3.73 Diff .... So the ECU will always think I'm going about 20% Faster when I'm not ....
and may not shift the Autobox gears up/down at the correct time and have an affect on when it kicks down and not. So I want to modify the output of the SP2 so my ECU thinks I'm going
the Speed I actually am with my Diff.

The SP2 Sensor on the gearbox is a 4PPR one I'm very sure..... is there a circuit I could build that could modify the output of this to make my ECU think I'm going the correct speed based on what diff I have?

Would there be a problem in doing this ? For example if the ECU might not agree with the Output of the SP2 and the Overdrive Direct Clutch Speed Sensor?

Thanks.

[madmont]

Why would you bother?

[HAVABEER]

i to would want to know this for my soarer, as i have the same issue with my soarers electronic dash showing about 10% faster after my diff swap.

i bought an apexi rsm unit and have that in my center console but it would be nice if i could change my actual dash

[Z2TT]

Hi Havabeer.... I'm not sure how it differs for the Dash Speed Sensor perhaps for your purpose maybe you can swap in another plastic gear from a car that had a similar diff ratio to yours?

My situation is for the 2 Wire Sensor that I want to modify the output of.


Madmount - Instead of not bothering (Like many people do) , I am looking to do things correctly.

The ECU uses feedback from sensors in the engine and gearbox to know when to shift up, shift down... when to hold gears for longer etc before shifting.
It uses sensors like Water Temperature, Throttle Position Sensors and Speed Sensors

The ECU needs to know the speed you are doing in order to shift at the best suited times. There is a Chip inside the ECU that contains data tables which determine
at which speed ranges and throttle position the ECU will change up and down into certain gears. The Speed Sensor No #2 provides a signal based on the revolutions
of the output shaft .... the faster it spins .... the ECU Assumes you are doing a higher speed.... this is all based on the Diff Ratio that the car comes with.
So by changing the diff ratio or having it in a non standard car .... it will affect at which speeds the gearbox will and won't shift. This is the reason why modifying the output
of the speed sensor will ensure that the ECU knows that you are doing the speed you are actually doing.

Here is a Shift schedule table, the ECU uses this data to determine shift points based on Speed and Throttle Position :

http://www.cygnusx1.net/Supra/Librar...aspx?S=AT&P=40

Here is some more info on ECT and Automatic Gearboxes

http://www.autoshop101.com/forms/h16.pdf

[madmont]

i to would want to know this for my soarer, as i have the same issue with my soarers electronic dash showing about 10% faster after my diff swap.

i bought an apexi rsm unit and have that in my center console but it would be nice if i could change my actual dash

You could always use a Jaycar speedo corrector for that. But it is a bit pointless modifying the signal the ECU recieves from the gearbox speed sensor.

[Z2TT]

I'll try the Jaycar one out, Cheers.

[big_zop]

Any reason why you cant swap to a different gear for the speed output from the gearbox?

[Z2TT]

It's not a gear driven sensor, it's a variable reluctance sensor that pulses every-time a tooth from inside the shaft moves over the pickup.

I wonder would the Jaycar Speed corrector circuit still work for this .... or do I have to look at something else.

Thanks.

[cambelt]

Hi
If yr sp2 is the reed switch type then the jaycar kit works fine.
The 4 pulse (and more) are all reluctor types and produce a AC voltage and its a little more tricky , something to do with using a pull up resistor .
Dave

[dumbass]

Just make sure the jaycar one can divide in fine increments

Sp2. Signal is a 4 pulse per output shaft two wire reluctor or inductive sensor

Spd is the signal form the dash which is a reed switch which is 4 pulses per revolution of the speedo cable if it had one
Or per revolution of the sensor on box for the dash
The gbox sensors can either have four or twenty pulses square wave to dash
This sensor has a pull-up resistor so the pulses got from 5 v to 12 v and are sent to the speedometer
Then in back of speedo the signal then converts to reed switch and its four pulses to ecu

Another problem I might run into is if sp2 and spd signals don't match up
I'm pretty sure sp2 is the main signal and spd backup
But if I find adjusting sp2 doesn't do anything then disconnect spd then play with sp2
And reconnect spd once u sort it out and see if it still works ok

I know sp2 and spd can do funny things if not right it's just trial and error
But u need to play with one signal at a time with other one disconnected so u don't get
A conflict of sensors

[Z2TT]

I wonder if everything will work fine with just the SPD Signal disconnected..... Unless ofcourse the ECU will go into limp mode if it doesn't get it... have heard on some Cars it causes problems shifting into overdrive. I know of people cutting it off totally and driving like that in Manual boxes.... not sure about Auto if it will just cause it to go into limp mode.

From what I know the Autobox part of the ECU Relies on SP2 mainly, without it wont even shift properly or at all.

My SP2 on the box yes I'm definitely it's a Variable Reluctance.... will the Jaycar unit work for that or not at all?

I'll probably adjust the Guage sender anyway since my Speedo is out from diff change anyway so the 2 signals will match up (SPD and SP2) in the end.

I was actually worried about the Torque Converter clutch speed not agreeing with the SP2 (If the ECU Compares them both and will go haywire if they are modified) -- I will worry about that one later though.

For the moment if anybody can confirm if the Jaycar unit works with Variable Reluctance type would be good..... or if there is any other unit from Jaycar or other places that do I'd like to know of it.

Cheers.

[dumbass]

the jaycar units are only 30 bucks so just build one and try it
they should do reluctor signals which is what u need
just depends on how fine an adjustment
the frequency shoudl be fine as its just a 4 pulse per rev of tailshaft
i sometiems use them for speedos but never for autos

if its your car just try different things as its all a learning curve

[George]

Transmission would shift at the right points no matter what diff you are running. I assume "right point" is engine torque/power/fuel efficiency related. The only thing you may want to alter SP2 output for, is the speed limit.

On late JZ series , SP2 is reluctor type with 8 pulses per output shaft's single revolution. Rsnning SP2+ wire through properly designed speedo corrector would work in most cases.

I have found on some 3RZ-FE ECUs (mostly on those for 4x4 vehicles) there're multiple speed inputs. However running only SP2 sensor is enough for normal driving.