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I recently replaced my engines Throttle Body by a larger (Chinese ebay) item.
It rotates in the other direction so I had to modify the TPS sensor.
For the potmeter part this was rather simple, just swapped the two outer pins in the plug.
But the ECU also wants to know when the throttle is closed and therefore there is a switch built in the TPS housing.
I modified the track in the plastic disc inside with two component glue and Dremel so the switch is now actuated in the right way.
It is very hard to fine-tune the exact position of the switching point with respect to the sensor angle (and therefore also the TPS potmeter).
I did my best but there still seems to be a difference compared to the stock situation.

TPS signal at idle should be 0.5V (it's somewhere in the manual).
This voltage is adjusted by rotating the TPS sensor on the housing of the TB and I adjusted the modified sensor accordingly when I installed it.

Idle seems to be good.
But!
At WOT I used to have 4.14V with the stock TB.
With this one I get only 3.24V.
I checked and the TB opens completely so it's not a matter of cable play.

Now that a lot of the factory ECU opcode is known it is probably known what the ECU does with this TPS value (at idle, at WOT and inbetween).
I would like to know what are the possible effect of a wrong TPS voltage.
Thanks.

TPS voltage range will mostly affect throttle enrichment (top end will be missing from extra enrichment) and tip in retard (retarding timing) from what I have seen on SR ECUs. I dont have these tables defined yet for CA18 however.

Hi Matt,

I didn't drive the car yet so I don't know how it reacts.
These two parameters that you mention are they dependent on throttle position or on throttle movement?
In the first case I should perhaps worry and try to fix, in the second I can give it a try and see what it gives while driving.

Thanks,

JC

Not sure. Dont know the CA18 code that well. SR20s have separate definitions for movement as well as position

If I remember correctly, there are same era TPS with movement direction opposite to CA18's..... RB20's ?

louiswun wrote:If I remember correctly, there are same era TPS with movement direction opposite to CA18's..... RB20's ?

Thanks for this info. I'll try to find out about these.

Meanwhile I found there was some play on the drive because the flat shaft didn't go deep enough into the TPS housing.
I fixed this and now the TPS voltage again goes from 0.5 till well over 4V.
Also the hysteresis on the TPS voltage is gone.

Thinking about all this made me wonder about the importance of the correlation between TPS voltage and idle switching point.
I don't think we really know.
From a top-end performance point of view it will probably be of marginal importance but still we wonder because we want to go deep into things isn't it
When swapping to a larger throttle body one can adjust TPS voltage to 0.5V at idle.
When pressing the pedal, the idle switch will go ON at a certain throttle angle.
With a larger throttle body, this switching point will occur at the same angle but that will correspond to a larger opening area than with the stock TB.
In case this would have noticable effect, it will most probably show up in cruising and in-town drive situations.

Matt wrote:I dont have these tables defined yet for CA18 however.

Would be nice