Fix one thing , break another - P1875

[thebanjoman]

Arduino, + ZCD , zero crossing detector is a must for VR coil sensors (most) as the signal  are tiny for sure low speed. of car. (a HALL sensor would be cake walk )

here is one example of the first part of the job, measuring frequency.

the next stop is scale up this new Freq. by 113% just using math.
freq-out = freq x 1.13  (now 13% more)
the set timer to freq-out


google how to use  Arudio to output a timer clock you control. (using freq-out)
and send it to a pin and connect that pin to VSS pin on TCM.

now the bad news, no spec on TCM
if lucky at least one pin might be ground and 2nd is input to TCM, vss1.

at the worse Ive done this and used transformer to emulate the VR sensor into TCM.
a 1:1 turns ratio transformer very very tiny one, 600ohms  rated, for audio work;.
I did the once to fool a FORD ECM to like my fake CRANK CKP sensor.

the VSS1 pins on the TCM
are not documented. pin # and color are, but not how TCM processes those pins, but in most cases is a ZCD in the TCM,   .

 Making changes at the trans speed sensor seems way above my skill level.

 Couldn't I make my adjustments on the speedometer side as that's what I am changing with my gear box device ?  

 Read the reed valve pulses and reduce them by 13%    ??

The speedometer is cable driven, and the suzuki parts used to have great sets to fit many head.
for different axle ratios used world wide. is the purpose.
that is G16 car
the J18, only has 1 gear set (plastic) for  only the one axle there are no other gear sets for the VSS2 cable drive to the cluster.
the SPORT is only sold in USA /Canada and Puerto Rico . MPH and KMH and use the same ratio drive, all. on the cable.  so there is no suzuki cure here, like G16s

you did it the only way on earth possible at the cable, a gear up box. it is. on the cable
VSS1 is not mechanical at all, it is electromagnetic, and  a pulse, only that is all it is. for speed.


There are only 2 VSS1 cures,  one is Analog electronics and other is digital processing and using some kind of re-scaling methods.

the reason nobody I know makes this is because, there are so many sensor types and worse so many TCMs.


here is what a 2 wire VR mag sensor looks like very small signal

I learn more with each conversation on this topic but I still may not be getting the full picture.   Apologies if I appear dense.

I understand the cable drives the speedometer and moves the needle depending on how fast/slow the cable is turned.  My Model A ford operates this way 90 year old technology so I think it's right.  

I'm spinning the cable faster by adding the speedo box.  spinning faster, needle moves higher on dial.  

And if I'm spinning the cable faster then isn't the reed valve opening and closing faster (pulse) now too ??

The pulses from the reed switch are sent to the computer aren't they?   I think so because I can see MPH reported on my ODBII scanner.   
While I am driving I can look at the ODBII MPH data and the needle of the speedometer and they are comparable.

I still can't get past the idea that both speed sensors are compared and if they differ more than 10% the P1875 code is generated. 
(the 1800 supplement book states this) 

I think i prove this, if I put in my 'speedo correction box' on the cable I get the errors.  if I remove it the errors go away.

I was hoping that if I could make the reed pulses appear as if they were never changed by adding the 'speedo box'  then the comparison would be within the 10% and the P1875 code would not be generated.      

I could also hypothesize that if my "speedo box" corrected say 8% and not 13% the errors would never be generated but the only way to prove this is to get another 'speedo box' of a different ratio change and put it in and try, but that's too expensive of a test.

This is not to scale but merely an example.

Reed switch pulses per second is 100 to be sent to computer.
Instead of being sent to computer it is sent to arduino. 
Arduino then sends 87 pulses to the computer instead of 100.

What is sent from the arduino is compared against the speed sensor in the transmission and it 'thinks' it's in spec and remains happy - 
Do not generate code.  

Im probably not thinking of this problem properly but I don't see why this wouldn't work.