running gauges in parallel with sensors

[dannyho]

I contacted the manufacturer of the ecm i have in question, about wiring an aftermarket gauge into the ECM wiring. and basically he told me (as an example) I needed to have two temp senders in order to run a stewart warner gauge, one for the gauge and one for the ecu to read. from what I can tell maybe this is because the ecm puts out a 5V sensor ground for the coolant sensor, the air temp sensor, and the TPS switch, whereas the SW gauge uses the 12v engine ground. I find it hard to believe that all the people running temp gauges and EFI have two senders, maybe its this ECU in particular?
I guess its not too big a deal, but it's still annoying. perhaps I can use one of the outputs of the ecu to send a temp signal to a gauge.

[Fuelie Fan]

It's not a ground thing. The grounds are made common inside the ecu. However, it is a very common issue, not just your particular ecu. Pretty sure you're going to be stuck with that.

[dannyho]

if this is the case, the ECU i have in mind has a lot of configurable outputs, so I believe I can probably come up with some way to get a gauge to work.
Here's a different question, similar lines though. I have a ton of aux input to work with as well, and I was hoping that I could snag a signal from one of the gauges. all the ecu sees in this case would be a voltage, or am I, once again, barking up the wrong tree

[Fuelie Fan]

does your ecu have analog in and out as well as digital in/out?

[dannyho]

I'm pretty sure it does. for input i dont remember, but reading a voltage isn't that hard. for output it can do pulse width modulation and I would assume if it can do that it can output a variable voltage. But as far as a digital output input, I believe that would only be through the serial interface with the computer. I can't really think of an application for a real digital signal output on a car, unless you meant something else?

[Fuelie Fan]

Digital input/output is simply on/off, and it's actually the most common. Fan controls, for example, are digital.

pwm outputs are "basically" digital outputs than be be cycled faster. They can also usually handle higher current draws, but that's not important for what you're looking to do.

True analog outputs are more rare and use completely different circuitry than PWM, so jsut because you have pwm doesn't mean you have true analog. If i were you i'd do a little more reading on just what capabilities your ecu has. You also need to find out if either the pwm or analog out can be made non-linear via a lookup table or not.

[dannyho]

ok, well as far as using the outputs to manipulate a gauge, it's probably more effort than it's worth. It would use up one of my outputs, and its not that hard to tap the manifold for another temp sensor.
using the inputs to log info from the gauges is a bit more useful to me. I suppose all it would take to find out if it'll work is to play with a gauge, a sender and volt meter, I guess it would be kind of a luxury, so I'm not going to stress over it.

[TPI Monte SS]

Just so you know, some of the factory setups use several senders for certain parts. My TPI setup has one sending unit to turn on the electric fans in the passenger side head, and there's another sending unit for the dash temp gauge in the driver side head.