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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars


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Old 10-05-2015, 01:53 AM   #1
turboS14kid
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Exclamation Need help aem vss issue

Hey everyone before I start Heres my setup info that relates to the issue
S14 1995
Rb25det engine
Wiring speaclities pro harness
Z32 tranny with rb bell housing
Z32 speed sensor 2 wire with ka knock sensor connector to connect to rb harness
V2 aem

Need help with my vss, I went in to aem to setup my 2 step and it wouldn't release out of 2 step rpm rang due to finding out my aem s2 is not getting a vss signal it sits at zero. so I set my 2 step to always off at the moment. SO I need HELP to setup vss tables to work and calibration for 300zx speedo in s14 with RB. Yes my cluster gets signal but it reads double the mph and my aem dose not get signal as show on laptop it sit at zero while driving. So any input would help or a screen shot of your Cailbration would be great.


Here my vss setup on the aem

Vss allowed diff 200
Vss cal*8 on
Vss calibration 56
Vss diff rest count 3
Vss filter on
Vss input T3
Vss smooth on
T3 falling edge on
T3 rising edge off
T3 h sens below 0 rpms
T3 L sens. Above 0 rpms


I have done research, I have not been able to find any information that has proven fix and relate's to my setup. I've seen a few threads on supra forum with simlar problems but they all end up never finishing the post and rebumped years later with a new person with same issue that needs solved.

Last edited by turboS14kid; 10-08-2015 at 10:44 AM..
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Old 10-07-2015, 03:42 AM   #2
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So there is the only way, that's to find mechanics
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Old 10-07-2015, 08:11 AM   #3
Croustibat
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on S13 and S14, the speed signal goes from the sensor to the cluster, and is then transformed to go to the ECU. If there is no wiring problem, it means the cluster is not able to process the signal sent by the sensor.

Your options are either to get a sensor that fits, or to use a speedo-healer. These devices plug between the sensor and whatever electronics that comes after, and convert common speed / rpm signals into other signals.
If you know someone handy with electronics, he could probably build one for cheaper. You need a µcontroler with an ADC input and DAC/pwm output depending on the signal you want, a voltage regulator and a couple of capacitors.
On s13 and S14, I think the speedo converts the sine wave signal from the sensor to a square signal that goes to the ECU, but this is from the top of my head and maybe i am confusing it with another car, so you need to check this in the FSM, there is a section with diagnostics that will tell you that.
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Old 10-08-2015, 10:39 AM   #4
turboS14kid
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Quote:
Originally Posted by Croustibat View Post
on S13 and S14, the speed signal goes from the sensor to the cluster, and is then transformed to go to the ECU. If there is no wiring problem, it means the cluster is not able to process the signal sent by the sensor.

Your options are either to get a sensor that fits, or to use a speedo-healer. These devices plug between the sensor and whatever electronics that comes after, and convert common speed / rpm signals into other signals.
If you know someone handy with electronics, he could probably build one for cheaper. You need a µcontroler with an ADC input and DAC/pwm output depending on the signal you want, a voltage regulator and a couple of capacitors.
On s13 and S14, I think the speedo converts the sine wave signal from the sensor to a square signal that goes to the ECU, but this is from the top of my head and maybe i am confusing it with another car, so you need to check this in the FSM, there is a section with diagnostics that will tell you that.
Thanks for the info it will help others

I found the problem, it turns out wiring speacialities dose Not have a returning wire to send vss signal back to the ecu on the pro rb harness. So I spoke to Yuri the answer to make it work with out voiding warranty is to run a wire to the dash harness yellow / green wire to the aem which in this case I would repin the aem pin 53 and add a pin since its empty spot that should be all. Hope that's helpful if any body else is having this issue
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Old 10-08-2015, 10:41 AM   #5
turboS14kid
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Originally Posted by Racerfanny View Post
So there is the only way, that's to find mechanics
Thanks for your spam, we Figured it out.
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Old 12-23-2016, 01:55 AM   #6
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Unfortunately, I can not help you! I'm not good at this. Sorry!((
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