Another wideband wiring question
 

Hello Gents,
Here are 2 easy questions for the Miata experts.
1-I have been reading many posts about wiring a wideband but it's still very unclear to me for the following reasons.
If you have the innovate LC1 with 2 grouds its easy, one goes to the Megasquirt/ECU sensor ground and the other to any ground, so you get a good sensor reading.
But...I have the LC2 unit which is dumbed down for stupid people and it has only 1 ground. And that ground has to draw several amps of power because of the wideband heater unit. Apparently some people burned their Megasquirt when they used the sensor ground. So where should I ground it? Engine?

2- Can I just remove the stock narrowband, screw the wideband, and attach it to the narroband harness? the connector provides 12V, ground and sensor wire. That way when I use the stock ECU I use the simulated narrowband signal, and when I plug my MS I use the wideband output and the signal goes through the car stock harness. is that doable?

Cheers
Seb

Connect the 12V and GND to the power window wiring.

If it's only temporary, you can screw the WB sensor into the NB location but it wont last long, too much heat, which is why WB sensors are mounted further along the downpipe.

Since most WBs are mounted further along the downpipe, most guys bring the wires up through the gearstick turret so you'll have the centre console out making tapping the power window wires easy.

I used vampire taps for this, though frowned upon by many, the power window wires are thick enough to negate any negative issues with vampire taps (ie. on smaller wires, vibrations may eventually cause them to sever the wire).

Yep I know about the heat issue, it's only temporary so I can learn how to use it. I was also thinking about putting it after the cat to have colder temps. How much does the cat really affect the signal? If it's 0.5AFR I don't care.

Power window it is, thanks! And what's wrong with using the stock wiring of the car?

I have ran many Innovative and AEM wide bands on the stock header in the stock position without issues.

1. Ground it to near where the sensor ground attach to the chassis, or whever. My AEM is grounded to the stud the ECU cover mounts to in my NA6 (downnin the footwell). You can calibrate it with the megasquirt, and the narrow band simulation mode won't car since the slope is so steep.

2. That is what I did and how I have been running since the spring. Works just fine. Don't put it after the cat. It is likely more than 0.5 difference.

Can anyone clarify if this is actually an issue? I've always heard that I should be grounding my wideband O2 sensor to the ECU if the sensor only has 1 ground cable (LC2/MTX-L).

I was in the same scenario as you with my MTX-L and investigated this. I wired the narrowband output of the MTX-L to the OEM narrowband harness, but used the 12V and GND from the power window wiring as mentioned above. This let me use my MTX-L as a replacement to my narrowband O2 sensor for a week or two until I installed my Megasquirt.

Although the stock narrowband wiring harness might provide 12V from the heater wires (there are 2 heater wires, 1 narrowband signal wire, and 1 signal ground), people mentioned you should use an ignition switched power source for the wideband and I had no idea if those heater wires would provide that. Therefore I went for the power window wiring.

I use the same 12v and grounds that my MS uses. Been doing it that way for years and never had an issue.

There's definetely a post out there where someone damaged their MS. (I read every post before asking questions). After you never know, most people are terrible with wiring...

So to recap:

1-To power the wideband, I can either use the power window or the stock O2 harness.
2-The header position is fine for short term (and its about to be winter in Boston so I'm not worried).

But for the ground, I'm still confused. If I ground to the power window then it's definitely not the ECU sensor ground. Shuiend you grounded it to the ECU sensor ground or normal ground?
Also, is the O2 harness 12V switched? if it is then everything is easy. I'm just worried that maybe the ECU turns off that 12V to maintain the stock narrowband sensor at the right temp.

Sorry if my post caused more confusion than intended.

1) Power the wideband with the power window harness (or cig lighter, or some other switched 12V source). The stock O2 harness (in the engine bay) does NOT provide a switched 12V source. Here are the 4 wires for the stock O2 harness (https://www.flyinmiata.com/support/i...ire_sensor.pdf) and I have no idea if that heater wire is a switched 12V.

2) I've used the OEM header position and many people use that position as Shuiend mentioned.

For the ground, I only used the power window ground before I installed my Megasquirt. When I switched to the Megasquirt, I moved my MTX-L wideband ground to the Megasquirt ECU sensor ground wire. I believe this is where you mentioned someone damaged their Megasquirt by grounding the wideband to the Megasquirt ECU sensor ground wire. However, I've stuck to the Megasquirt ECU sensor ground wire with no problems.

Ok, did you put a vampire clip on the sensor ground too?

About the stock harness, I assume the 2 white cables are 12V and non-sensor ground,no? If that's true then does anyone know if it's a switched source? Because the stock harness has everything you need and would make the wiring simple and reversible.

Just bringing this thread back up to request confirmation on something: for an NA6 PnP ECU, it's best to tap your wideband's power wire into the stock ECU harness at pin 1B (white/red wire), and tap for your wideband's ground wire at pin 2C or 2D (both wires black/lt green)?

yes

I actually had better results grounding my wideband (running narrowband more) directly to the car firewall surprisingly, next to the wiper motor.

What are the results you qualify as "better" or "worse?"

The power wires for the heater circuit should be landed at battery or main distribution panel to avoid overloading a circuit not designed for the amperage that they can pull. They should also be fused as you are creating a new circuit.

"Vampire clamp" or splicing into power wires from an existing OEM circuit for the purpose of powering aftermarket O2 heater is a recipe for overloading that "tapped" circuit.

Each OEM circuit is designed and it's fuse spec'd for the load it is expected to support in an OEM configuration. Adding extra load to established OEM circuits has the very real potential to overload those circuits.

EDIT: To answer OP's question, If that single ground is a high amp ground for the heater circuit, do NOT connect it to a signal ground unless you want to buy a new ECU. Ground it to battery (-). You do not have to ground it literally at the battery, an engine or chassis ground may work just as well, but don't assume it will. Always check with a multi-meter the resistance from the ground point you have chosen all the way to the Battery (-) post. Preferably you would like to see <1 Ohm.

Each person's car will have various states of corrosion on the ground points or disrepair to the ground straps that tie all of these components together. Assuming what worked for one person will work for you is how you burn things down.

If you don't have a multi-meter, buy one. You shouldn't be doing anything electrical without one.

And people wonder why the same question gets asked over and over...because it keeps getting answered differently over and over. :cry:

True, you think people would stop and think "Hmmm, I might need a better qualification than "hey it worked for me" to answer questions like this."

There is a professional's answer, and there is the answer from some guy who did it in his driveway with limited tooling and "hey, lucky me, it worked and I didn't burn the car down."

Which answer are you going to trust?

The stock wiring was designed to provide high amps to the narrowband O2. There is no need to splice anything at all, I just bought an 02 extension that I cut so I keep all the stock connectors and everything is reversible. You should just ground on one of the sensor ground areas in your engine bay instead of using the wire in the harness. The results are better that way because I have measured a ground offset if you use the signal ground of 0.4V which is huge for a 1V signal, and the motor was not running as well. No it will not burn the ECU but it's not good for it either.

Clear enough?

i actually still dont understand why most people splice into their harness when you can keep everything nice and tidy

Going to bring this back from the "just dead" - but I like where you're going from here. DIY recommended that I ground to the cylinder head (1999 miata), as far as the other wires...0-5V signal, and 12v switched - can I just cut up an o2 extension wire and connect the WB signal to the narrowband signal (which goes straight to ECU-mspnp2), and use one of the heater wires for the switched signal - or should I find that power window switch power that others have mentioned?

Edit: Disregard heater wires comment - will tap into cigarette lighter switched 12v.

I only tapped in the existing wiring harness, it was designed to deliver high power to the stock narrowband O2 heater so it works great.