ledtool11

i just rewired my o2 sensor directly to the ecu, how do i make sure the ecu is getting a signal?

NZConvertible

Measure the voltage at the ECU. It should be close to zero with the throttle closed,
~0.5V at cruise and 0.8-0.9V under load.

Did you use shielded wire in the engine bay?

ledtool11

no, where would i find shielded wire?

ledtool11

bump

JackoliciousLegs

What if it's a turbo? 1V under load? Oh, and how close to 0. like .01 or 0?

VietFC

it should be the same as N/A

GregSL-SE

What is the purpose of a shielded wire?

WAYNE88N/A

The shield is to prevent stray EMF from inducing voltages in the wire that would skew the puny voltage signal sent by the O2 sensor. It's nothing more than a braided "jacket" that serves to shunt all unwanted EMF to ground before it can mess with the inner conductor's voltages. I think our CAS wiring is shielded too....

NZConvertible

Yep, it is.

Any electronics store should have shielded wire.

GregSL-SE

The Bosch O2 did not have a sheilded wire, am I in trouble?

WAYNE88N/A

Are you sure? I'd bet you just didn't notice it...

I know the Bosch p/n 12054 (direct plug & play for our S4's) had it...

It doesn't look like coax wire- that's a different type of "shielded" wire...Unless you're really paying attention, it looks just like normal wiring...Once you cut it open, or try to splice it, it becomes obvious...

GregSL-SE

The bosch I got had an exposed wire ready for connecting

WAYNE88N/A

Yeh, the shielding doesn't "jump" across the connector, 1/2 of the run will be grounded through the sensor/ manifold itself, while the ECU harness 1/2 is grounded near the ECU, IIRC...

GregSL-SE

So in a sm@rt @ss way- you're saying the connector won't pick-up EMF? And what is IIRC?

WAYNE88N/A

Wasn't trying to be a smart *** at all, it's understandable when reading the written word with no voice inflection, each individual is going to read it the way he/she wants to "hear" it in their head...If we wanted full run shielding on our O2 sensors, we (Mazda) could have used something akin to a coax-type connector, or, similar to an aircraft, a special connector where a small collar fits over the "splayed" shielding, and physically/electrically connects to the opposite plug (these connectors are a PITA to work with, BTW).

I don't know why the shielding wasn't "spliced" across the connector, my best guess would be that limited EMF interference would be encountered at the location of the connector (maybe that's why the plug/harness runs to the back of the engine area in OEM applications, eh?)

IIRC=If I Remember Correctly

ledtool11

How close to the ECU do I have to use the shielded wire?

WAYNE88N/A

I've never ripped open my harness in there to see exactly where the shield seperates & grounds, but I remember seeing a pic of it somewhere, and it wasn't very far away from the ECU at all. The only thing I can think of in that area that would give you EMF problems would be the blower motor, but I would think that's far enough away not to cause problems. It's mainly the ignition system EMF we're trying to steer clear of with these shields...

ledtool11

ok, thanks a bunch, im gonna go get some shielded wire as soon as I can