O2 sensor wire runs under the manifold right?
 

I've been searching and looking at pictures of people's NA's with their intake manifolds off and from what I can tell (grainy pics) the O2 sensor wire on S4 NA's run under the intake manifold correct?

I'm very familiar with the fact that I can just run the wire directly to the ECU but for whatever reason, thats not what I want to do.

(Icemark - I've grown to trust your judgement on electrical issues so... if I should just run directly to the ecu for any reason other than it just being easier then please say so)

As long as you maintain the integrity of the shield, and ground the shield near the ECU or at the sensor itself (if you're bypassing the stock harness, you'll need only one shield run), you should have no problems running directly to the ECU's input...

Having said that, I'm left to wonder if the Mazda engineers knew exactly what they were doing, and designed that particular length of O2 sensor wire into our cars because the ECU is calibrated for a particular voltage drop over a particular length of wire. Maybe I'm just being paranoid again, lol...

FWIW, mine runs up to the firewall from the sensor, travels along the firewall for about 1', then dips down to the back of and then under the UIM to the OEM harness. Small tie wraps make this possible...

ok, so now I'll just need to cut the harness under the UIM and find the rest of my O2 sensor wire and splice em together.

Just remember that it is a sheilded wire.

Is that a suggestion toward identifying it after cutting the harness tubing or when splicing? (I'm no electrician)

I wired my o2 sensor straight from the sensor to the ecu and spliced in at the harness, I havent gotten any o2 CEL's since then. Im guessing its working

Actually, that brings up an interesting thought- since there's not any EMF inducing components in that area between the exhaust manifold and the firewall opposite the ECU, you might be able to get by without the shielding if you're running straight to the ECU. Just keep it down, as far away from the windshield wiper motor as possible. Not recommending it, just a thought...

Hailers, you like to tinker- try it :)

mine runs along with the brake booster lines and all that other stuff

Not exactly "straight to the ECU", is it? Where did you go through the firewall at?

You kept it shielded, right?

I went through the large grommet by the drivers side footwell then back behind the center console and down into the ecu. Its just a plain wire with a plastic jacket on it. What do you mean by shielded?

Aw shit, lol...

A shielded wire is a normal wire with an insulated jacket with an extra metal braided wire surrounding the jacket, then it too is surrounded by its own jacket.

Used in applications where the voltages are so low that any outside electrical interference caused by spark plug wires, coils, electric motors, large capacitors, etc could cause voltage fluctuations in the wire...

The shield "grabs" these outside interferences and shunts them to ground (all shields are grounded) before they can affect the low voltage signals...

They are all over aircraft wiring, but there are only 2 circuits that use them on our cars as far as I know- the O2 sensor, and the CAS wiring...

As long as your wiring is at least a foot away from any spark plug wiring, and at least 6" from any motors or coils, you should be OK. I'm guesstimating distances here based on past experiences...

Hmmm, thats very interesting, is there any access into the passenger cabin on the passenger side of the car?

If you drill a hole, lol...

I drilled one for the line for my vac gauge...

:rofl:

My vac line goes the same route as my o2 wire haha.