No TPS, but TPS "creep"?

[opethmike]

Jim,

That solved my issue. Thank you very much.

Owen,

I've looked at it, but my understanding of timing is VERY rudimentary, so I'm afraid I can't offer much useful feedback

[jangell]

In case you're wondering why you had to ground it, and why you got weird values when it wasn't, I'll throw in my novice electronics knowledge here: Basically, the MegaSquirt expects the input to be between 0v and 12v. When it's not connected to anything, the value is "floating", meaning that its value is undefined (I think it actually acts as a radio antenna and generates slight voltages from random RF, but I could be wrong). This shows up as seemingly random values in the signal. Floating inputs are generally considered bad for this reason. Tying it to ground (i.e. "pulling it down"; "pulling up" would be tying it to 12v) ensures it always has a constant value of 0v.

I'm sure someone actually knowledgable like bitsyncmaster would be able to provide a more accurate answer than this.


Incidentally, I'm hoping to start my EFI conversion some time in October; I got rails from Owen and fittings from JEGS, but I need to save up a bit more before I can order the MS, sensors, fuel regulator and whatever else I need. I was thinking of going with a TPS, but I'm not really sure.

-- Joe

[Bitsyncmaster]

The input impedance on most microprocessor analog input pins is quite high (> 50 Kohms). So the humidity in the air can change what value of charge an open input pin will see. Of course the car has a lot of wiring harness and high impedance will pick up and charge high impedance with different voltages.

Normally the designer would design a jumper to ground the pin if not used. Or he can option via a user function to disable that part of the software to alway load zero. Another option the designer can take is program the input pin as an output if disabled.

It's still better to not leave input pins floating. Voltages greater than the VCC or less than ground can feed through the micro and affect other hardware inputs.

[dmc6960]

Basically, the MegaSquirt expects the input to be between 0v and 12v.

Almost. The TPS POT runs off of a 5V reference voltage supplied by the ECU. Other external sensors (air and engine temp) are dual wire, and run from a reference ground in the ECU, to a calibrated pullup circuit to give and approximate input range of 0-5v for them.

[dmc6960]

Have any of you guys tried/looked at my timing calculations in the forum? Would be interested in getting your feedback.

I'll get there eventually...