Multiple 02 sensor questions

[2.216VTurbo]

First I'll admit that the electrical systems on my TD cars are NOT my strong suit In theory I'd like to monitor the AF ratio in each cylinder on my 87 GLHS so I have an o2 bung welded onto each header tube. Then I had a local guy make up a Dawes style gauge with essentially four A/F gauges in one little box (16 lights total, four sets of red, yellow,green and blue). The box has power, ground and four sensor feed wires coming out of it. So far so good.

Now a four wire 02 sensor has: (feel free to correct me here)

Black-.1-1.0 sensor voltage output
grey-ground
two whites- both for heater?

I have an 02 sensor in each bung but only one is hooked up to give readings to the ECU (car is converted to SMEC if it matters)

Here's the question, to get sensor voltage output out of the other three, do I need to power up the 'heater' function of the sensor? Or can I just hook up the ground, one of the whites to power up the sensor, and the sensor output to my custom A/F box? I'd ask the guy who made the gauge but he moved away a couple years ago. I'd rather not have the draw on the electrical system of four actively heated 02 sensors. I don't mind if the 'extra three' take a little longer to get up to temp.

An even sillier question is, do I even need to put voltage to the three extra sensors, don't they make voltage just based on the heat energy applied to them? If not, how do the old one wire sensors on the early cars funtion? That single wire has to be sensor voltage output right??

Alan- I can build a 400 HP motor from scratch, I'm just electrically challenged

[pooky]

First I'll admit that the electrical systems on my TD cars are NOT my strong suit In theory I'd like to monitor the AF ratio in each cylinder on my 87 GLHS so I have an o2 bung welded onto each header tube. Then I had a local guy make up a Dawes style gauge with essentially four A/F gauges in one little box (16 lights total, four sets of red, yellow,green and blue). The box has power, ground and four sensor feed wires coming out of it. So far so good.

Now a four wire 02 sensor has: (feel free to correct me here)

Black-.1-1.0 sensor voltage output
grey-ground
two whites- both for heater?

I have an 02 sensor in each bung but only one is hooked up to give readings to the ECU (car is converted to SMEC if it matters)

Here's the question, to get sensor voltage output out of the other three, do I need to power up the 'heater' function of the sensor? Or can I just hook up the ground, one of the whites to power up the sensor, and the sensor output to my custom A/F box? I'd ask the guy who made the gauge but he moved away a couple years ago. I'd rather not have the draw on the electrical system of four actively heated 02 sensors. I don't mind if the 'extra three' take a little longer to get up to temp.

An even sillier question is, do I even need to put voltage to the three extra sensors, don't they make voltage just based on the heat energy applied to them? If not, how do the old one wire sensors on the early cars funtion? That single wire has to be sensor voltage output right??

Alan- I can build a 400 HP motor from scratch, I'm just electrically challenged

You only need power to the sensors for the heating elements. O2 sensors work like pyrometers in that the dissimilar metals in the sensor create a small electrical current when heated. You'd be much better off with 4 pyrometers or probes rather than 4 O2 sensors.

[87glhs232]

Are you saying that the ECU only see's one cylinder? I think if I wanted to monitor each cylinder, I would exhaust temp each, and keep the O2 in the stock location, so it see's a blend of all cylinders.

Black-.1-1.0 sensor voltage output
grey-ground
Some people report that theirs were black ground. Mine was grey.
two whites- both for heater?
Correct. One gets 12v, the other gets ground. Doesn't matter which.

The grey and black are the sensor circuit, the two whites are the heater circuit.

One wire o2's rely on the body of the sensor being grounded to the exhaust mani. The 1 wire is the sensor output. Heat is supplies by the exhaust. 3 wire sensors added a heater element, but still relyed on the sensor body being grounded. 4 wire added a dedicated ground for the sensor circuit.

[2.216VTurbo]

Yep, the ECU is only seeing one cylinder. I've kept the boost pretty conservative for the first 2K miles. The external gate is set to 10PSI and 16PSI was the max the motor has seen on the dyno and there was a wideband set up keeping us honest

Once I figure out which is leanest, I'll run the sensor there.

I am running an EGT as well it just seems slower to respond than the LED style gauges and you kinda have to watch it closer than just checking for green lights out of the corner of your eye.

Thanks for the 02 Sensor 101 class They will be a bunch easier to wire the other three up now that I know I only have to ground them and hook up the output wires to the gauge. After that, it'll be time to add some boost

Alan

[Tony Hanna]

Definately a neat setup. I'm curious to hear how it works out.
As for sensor warm-up, I bet it'll happen pretty quick even with the sensors unpowered being that they're upstream of the turbo.

[JDAWG]

i second keeping a sensor in the stock location for the smec and using the seperate four for the a/f gauges only

[2.216VTurbo]

Stock location would be fine but there is no swing valve assembly anymore This is a full tube header set up with an external wastegate so I just kind of have to go with it...

I'll do some wireing in the next couple days and post the results of comparing the A/F mixture of one cylinder to the next. Pretty much be useless to anyone but me as I am running a custom sheet metal intake that feeds from the passenger side first (#1 cylinder). It just worked better that way with my turbo location (over the trans) and intercooler set up.

Again guys thanks for the electrical tips-I am seriously deficient in 'E' tech.