Throttle position sensor
 

Does anyone know if the voltage output from the throttle position sensor on my Silvia is suitable to be used for the SAFC II. With the car being fitted with automatic transmission there is a second plug under the throttle contacts. The middle wire that is light blue gives an output of 0.5 Volts with the throttle closed and very close to 7 Volts with the throttle fully open.

I have been looking into this on T'internet and the max output voltages from other vehicles seem to be no higher than 5 Volts so before I hook up the grey throttle sensor wire I need to know that it won't fry the SFC II.

I have emailed Apexi but have not had a reply. I have also tested the voltage output on another Automatic Silvia and that gives the same output voltages. Any help will be appreciated.

i always thought the s12 TPS was a throttle position SWITCH rather than throttle position SENSOR (although may be wrong). the s13 TPS is a sensor iirc.

as far as i'm aware,you need to use an s13 1 or 1 of the universal ones available for aftermarket ecu's.

dont remember wiring in the TPS on the s12 i fitted an SAFC to, just rpm and AFM

like I said they are only on the automatics :rolleyes:

true..auto has extra bits to run the gearbox though

wiring the SAFC without a throttle sensor signal is only half the job as you can't set the high throttle RPM values so you can make the car right for cruising but not driving hard, or you can set it for driving hard and end up never passing a petrol station.

ahh, you're using one of the newer sort. I fitted a 5 dial type

I'd say find a TPS from an auto s13, the 7v signal wire you've identified is I think the wrong one for this.

The remaining two wires give a constant 0 Volts and 12 Volts.

Paul set it for HARD DRIVING! you know you want to :D

I am waiting to see if Apexi email me back if not I may try to make a potential divider with some resistors and hope it doesn't effect the signal doing to the automatic transmission control unit.

The S12 auto TPS is simply 2 switches in one. It provides a full throttle signal and an idle signal, with no variance in between.

If you use an S13 one, it has an additional plug come from the rear of the the unit then provides the variable signal.

Only issue, is that you may need to supply 5v (guess) to it for the signal to be similar to how it would be on an S13.

The answers to your problem are in the S13 service manual. Rather than look at the wiring diagrams if you look at the tests for the TPS it should show the switching side and the potentiometer side of things.

Thanks 30 PSI. The throttle contacts on my S12 Auto and on the other one I have do have an additional plug underneath with a voltage that varies from 0.5 Volts to 6.95 Volts depending upon the position of the throttle and I was hoping to tap into that signal for the SAFC II. I also haven't had a reply from Apexi yet.

So your auto TPS also has the variable bit on it, but uses 7V as a base? Didn't know that, I thought it just had the idle and full throttle switches.

I guess Apexi is only happy with a 5V base?

The input voltage to the TPS is battery voltage and I have just got an email from a friend in America who has telephoned Apexi for me. The reply he got was as follows:
In regards to your question about the throttle position sensor reading 6.95V
and if this would damage the SAFC2 unit. This would not damage the unit. The SAFC2 unit can only read a 0 - 5 V signal, so therefore, the only downside to your TPS sensor reading 6.95V is that the SAFC2 will not be able to read/monitor voltage above 5V.

So I can use the wire but anything in the last fraction of travel of the throttle will not be measured correctly. That should do for me because the car seems to be running rich enough at that point on the existing fuel map.