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-   -   VTPS, IAC, and Wiring questions (https://www.miataturbo.net/ecus-tuning-54/vtps-iac-wiring-questions-59565/)

g_reichow 08-05-2011 08:58 AM

VTPS, IAC, and Wiring questions
I have a TEC-2 standalone controlling my 1.6L miata with a 1.6 Auto throttle body. Currently the IAC is controlled by the factory ECU, everything else (fuel/spark/O2, etc) is controlled by the TEC-2.

I had originally wired the TPS into the factory harness as such:
Manual < -> Auto

black/green < -> black/green
red < -> green/red
green/white < -> red
Tec-2 TPS < -> red/black wire

Where the left column is the factory harness and the right side was the sensor side of the wiring.

Admittedly this wasn't right and not providing me good resolution as the TEC-2 would show between 0-1.6v output from closed to WOT. So working through the factory manual and using a 5V output from the tec-2 we provided 5v, ground, and VTPS signal to the tec-2 and cut the OE ECU out of the loop.

Initially this worked great, and TPS was good. However now when starting the car, it will start and die at any attempt to idle. My question is this: If the factory ECU doesn't see a TPS signal on startup, will the IAC act erratically? This car was running fine, no map changes, it has just gotten progressively worse the more I've driven it since the change. I can put it back to the prior wiring but wanted to get it "right".


tldr: Changed TPS wiring, factory ecu doesn't see TPS, will this cause IAC issues?

Braineack 08-05-2011 09:28 AM

it really shouldn't cause issues, only that the stock switch doesn't tell the ECU that much. But in this case, the stock ECU is providing the power for the varible resistor on the TPS, since you connected the green/red and red wires together; so that's probably the issue.

the green/red is the signal back to the stock ECU that tells it if you're at 0% TPS or not. The input floats high (12v) until the the tps grounds, then the ECU knows you're TPS is closed.

The RED wire on the vtps is supposed to be the 5v source, so putting it at 1N on the wiring harness probably is messing up the signals.

I'd rewire it like this:
RED should match RED.
BK/GRN should match BK/GRN
GRN/RED should have it's own 5v source.
and RED/BK should go back to the TEC-2.
Nothing on GRN/WHT

This way the stock ECU will know when you're at idle and "part throttle", the tec-2 will get the corect 0-5v signal and all will be well in the world.

g_reichow 08-05-2011 12:56 PM

Thanks for the reply. I'll try moving those around tonight. We did rewire it already but I was concerned that the lack of a throttle closed signal was causing it to stall right after startup.

I'll try to get new wiring diagram mapped tonight. I just can't figure out why it wants to stall out of idle. I need to get this thing through emissions in next couple weeks.


Braineack 08-05-2011 01:03 PM

there's a 5v source on the AFM connector FWIW.

g_reichow 08-05-2011 02:14 PM

I've got 5v sources to spare via the TEC-2 (including one that drives the MAP right next to the throttle).

just seems weird that this rewire would work initially then cause the car to not run on after startup. I'll correct this then worry bout other things (3y.o. fuel for instance)


g_reichow 08-07-2011 03:33 PM

Verified the wiring that wasn't the issue. Got a good datalog with the TEC-2 and using the engine monitor I added a 40% Gamma offset and the thing stayed running. So I know I have old fuel in the tank (closer to 4 years old now that I do the math). So either I have a dirty fuel filter, incombustible fuel, or fouled injectors. I'll drain the fuel, put fresh in, and change the filter first.


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