Where is my speed sensor wire?

[AaronsSupraMKIII]

I am trying to locate my speed sensor wire. I pulled a code 42 on my transmission diagnostic, which is no suprise since my Speedo isn't working. I pulled my gauges out and drove around the block, speedo cable isn't turning at all. Anyways, I will replace that later on, but I need to find my VSS (speed sensor) Wire. I pulled up a wiring diagram of a ECU, but it is different than the ECU I have. Mine has plugs labeled 26p 16p 22p. It is a 91 turbo/Automatic.
Can someone give me a link or tell me which one is the VSS? I have my dash all tore apart, so a quick response would really be appreciated.

BTW When I took the glove box off to access my ECU, I found a HKS FCD piggybacked on the ECU! It has a manual set screw dial on it. Is that a good one? Does it work in conjunction with the EBC? Thanks!

 

[Fletch124]

If your speed cable doesnt work then mostly likely the short part of the speedo cable broke. Go to toyota and have them order you the short part of the cable, its under $20.

 

[Idealsupra]

if you are automatic and your speedo cable is broken that is your problem. the speed sensor the auto uses is located in the gauge cluster on the speedometer.

 

[dbsupra90]

dammit my internet crashed and didnt post my reply.

anyway, yes the speedo is causing the problem.

there are 2 speed sensors, one from the speedo and the other from the rear sensor. the ect ecu looks at both of these signals (sp1 and sp2) to see if they are the same. if not, it will set the tranny code.

you need to fix this as soon as possible. if the code is set, the shift tables will be screwed, it will not downshift properly, and the converter will not lock. this all leads to poor performance and poor mpg.

the vss wire you are talking about is a pink wire at the ecu. this isnt the signal seen at the ect that is setting the code. and regardless, neither will have the signal until you fix the speedo cable.

here is a color diagram for the 91

http://www.mk3.us/dave/tech/ecuwire3.gif

there is also ecuwire 1 and 2 for future reference.

here is the ecu pinout for a 91

http://www.mk3.us/dave/tech/supradiag89.jpg

here is a diagram of the ect ecu

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=AT&P=21

 

[AaronsSupraMKIII]

dammit my internet crashed and didnt post my reply.

anyway, yes the speedo is causing the problem.

there are 2 speed sensors, one from the speedo and the other from the rear sensor. the ect ecu looks at both of these signals (sp1 and sp2) to see if they are the same. if not, it will set the tranny code.

you need to fix this as soon as possible. if the code is set, the shift tables will be screwed, it will not downshift properly, and the converter will not lock. this all leads to poor performance and poor mpg.

the vss wire you are talking about is a pink wire at the ecu. this isnt the signal seen at the ect that is setting the code. and regardless, neither will have the signal until you fix the speedo cable.

here is a color diagram for the 91

http://www.mk3.us/dave/tech/ecuwire3.gif

there is also ecuwire 1 and 2 for future reference.

here is the ecu pinout for a 91

http://www.mk3.us/dave/tech/supradiag89.jpg

here is a diagram of the ect ecu

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=AT&P=21

Thank You!!! You just saved ma alot of work, and money. I am only getting 12mpg!! Now I know why. I am also dying when I downshift, and unsteady idle. I have been looking for vac leaks, but I appear to be good in that area. I am glad you sent the links. I need the speed sendor wire to go my navigation system, it has to have it to work. I ill order the speedo from toyota monday. Is it always the short part by the tranny that breaks? Thanks!~ Aaron

 

[dbsupra90]

glad i could help

it could be the tranny side. hopefully so. its the easiest to replace and the cheapest. might want to take a look and make sure the downpipe isnt near the speedo cable. ive seen them melt before and cause the problem.

good luck

 

[AaronsSupraMKIII]

glad i could help

it could be the tranny side. hopefully so. its the easiest to replace and the cheapest. might want to take a look and make sure the downpipe isnt near the speedo cable. ive seen them melt before and cause the problem.

good luck

Thanks, I will. Do you know what a FCD is? I have read a few posts, and they don't seem like a good thing to have. I know is has something to do with fuel cut, but dont really understand any of it.

 

[dbsupra90]

yeah im not a big fan of an fcd

fcd = fuel cut defender

the airflow meter measures air flow in frequency (hz). the ecu uses this measurement to know how much air is coming into the motor.

the fuel cut function is a fail safe. if say for some reason the wastegate fails, boost will continue to raise to very high levels that can damage the motor. the ecu does not read boost, only the frequency, so this is what it uses to make sure the boost level is safe. if the ecu sees around 1600hz (roughly 13psi) it will trigger fuel cut to save the motor.

what the fcd does is more or less a frequency filter. it prevents a signal high enough to trigger fuel cut from getting to the ecu.

now why this can be bad. like i said, the ecu just sees the frequency and bases the fuel and spark maps according to the air flow it sees. there is a little more to it than that, such as throttle position, coolant temp, etc, but basically it boils down to the air coming in the motor. say you want to run 17psi, which we will just call 2300 hz. the fcd will filter the frequency going to the ecu at say, 1200hz, so it will not trigger fuel cut. sure, you wont hit fuel cut but here is the problem. the ecu will only compensate enough fuel for 1200hz, which lets just say is 6psi. see the problem? you have a lot more air coming into the motor without the fuel to back it up.

there are much better ways around fuel cut than using an fcd. having an adequate fuel system to back up the boost, then something like an afc to tune around fuel cut. even still, these are only good to a point. if you tune too much out it can cause issues as well. its all a balancing act. the most common is using a lexus afm and 550cc injectors. the afm will flow around 25% more air, but the 550cc injectors will flow around 25% more fuel to balance it. this afm has a larger unmetered air (air getting into the motor that isnt being read by the airflow meter) and will raise the boost level of where fuel cut occurs. but again, you have the larger injectors to make sure you have the fuel to back it up.

i hope this helps some. im by no means an expert at this stuff. just been into building and tuning supras for the past 9yrs or so. and i probably made it sound more complicated than it really is. but in a nutshell, thats basically how it works.

 

[AaronsSupraMKIII]

I see. Why would anyone wanna take an engine safegard out that might very well save you from blowing up your motor? I dont see any advantage to this FCD, so I am going to uninstall it. That wont effect my Greddy profec spec II will it? I bought the car with these already installed. The guy didnt even tell me about the FCD. I think it is set to "0" anyways and not functioning because my boost controller defaulted to a high setting when I turned it on, and I hit fuel cut, and my BOV vented.

 

[dbsupra90]

well, to make big power, or atleast to get more than 12psi you have to get around fuel cut. but the fcd is not a good way of doing it.

it will not effect the operation of your boost controller. but if you are boosting and the car studders and check engine light comes on, dont be alarmed. thats the famous "turbo pressure abnormal" code, aka fuel cut. not sure of your mods, but dont get carried away with turning up the boost. id keep it around 10psi or so for now.

btw, thanks for the kind words

be sure you check out the FAQ section on this forum. lots of good info there.

 

[AaronsSupraMKIII]

It was actually a total accident that I hit fuel cut. I bought the car and told him it was my first turbo, and that I know nothing about them, so he would have to show me how to work the boost controller. He told me it would be best if I didnt touch it until I learned more. I agreed and said to set it to a safe setting, well it turns out he turned it totally off instead of setting it lower. I red up on it, and turned it on. I set it to 6psi. Figured that should be safe enough. Then the next time I started the car up, It had alot more take off and boosted more. All the way to fuelcut. LOL It defaulted to 20 psi when I started the car back. Why I dont know. Anyways, the engine light came on, and the BOV vented. (which scared me to death cause I thought I blew a head gasket or something.) So everytime I start the car now, I double check the setting on the controller. I dont like hitting fuel cut..HE HE