O2 sensor wiring

[tj]

Background: 1970 302 engine loosing Duraspark ignition, & 4 barrel carb which is being replaced by a 1993 Mustang EFI system.

Next on my to-do list is to fabricate an O2 subharness that goes between the '93 main harness and the sensor connectors. I have no problem matching up the wires coming from the computer connector but the wires from the O2 sensors are confusing.

QUESTION: The O2 sensor has 3 wires, one black and 2 white. One should be ground, one 12V for the heater and one the sensor output. The plug has the connectors arranged in an "L" shape. I'm assuming the black wire is ground. HOW do I tell which white wire is 12V for the heater and which is the sensor return???

BONUS QUESTION: I am using a transfer case behind my T-18 that is incompatible with the Ford rev sensor unit. How big of a problem am I looking at not having the RPM sensor?

Thanks

TJ

 

[bob_lafrentz]

I may be wrong, but I don't think the ford EFI system uses RPM's. It can utilize a VSS (vehicle speed sensor). Some use it and some just skip it and have no problems.

I am in the middle of an EFI conversion and found that WildHorses has an aftermarket VSS that attaches to the back of the speedo. Then, you can use a stock speedo cable to go between the speedometer headunit with VSS attached and the transfer case. This set up might work for you. Any speedometer shop should be able to custom make a cable for you with a Ford speedo head connection to whatever transfer case you are going to use. It shouldn't cost that much. I know I have spoke with the shop that Advance Adapters plugs and they seem to really know there stuff and are very reasonable. Hope this gives you some ideas.

 

[SaddleUp]

The stock EB cable will fit a stock VSS if it is drilled out a little larger. That's what I did and it's been that way for well over a year. I haven't had the VSS wires plugged in though for 6 months or so. (I never got around to extending the wires when I put the doubler in) I'll probably just leave it off when I put a new cable in. (I managed to cut mine in half when I got a bit wild with the sawzall)

 

[tj]

Thanks for the help on my afterthought bonus question. It gives me some ideas of how to handle it.

Of course its all for not unless I find out which white wire from the O2 sensor to the sensor connector is for 12V to the heater and which white wire is the O2 signal output. It would have been real handy if the O2 sensor manufacturers colour coded their wires to the connector.

3 pin connector, with pins arranged in an L shape. 3 wires from the sensor, 1 black 2 white. I presume the black one is ground but which white one on the connector is 12V & which is singal out?

Thanks

TJ ?:? ?:?

 

[70_Steve]

3 pin connector, with pins arranged in an L shape. 3 wires from the sensor, 1 black 2 white. I presume the black one is ground but which white one on the connector is 12V & which is singal out?

See if this helps.
http://fordfuelinjection.com/files/EFI_harness.gif

 

[Broncobowsher]

Black wire is signal
2 white wires are for the heater (no polarity for the heater)
Gray is signal ground (if a 4 wire sensor), 3 wire sensor uses the exhaust sytem for signal ground.

 

[tj]

Black wire is signal
2 white wires are for the heater (no polarity for the heater)
Gray is signal ground (if a 4 wire sensor), 3 wire sensor uses the exhaust sytem for signal ground.

:-X Duh!!!

Black = ground is so ingrained into me that it didn't occur to me that it would be anything but ground unless I was working on a German car and I would check to see if brown were ground.

Anyway I just ASSumed that the black wire was heater ground THEN puzzled over the two white wires from the O2 sensor. Once I stop assuming black ALWAYS = gnd. and think of the heater as a resistive load that is not polarity sensitive then everything falls into place. %)

Thanks for helping out the slow student.

TJ

 

[Lttrbox]

Just have to throw in another comment about the VSS. I have been fighting a idle/stall problem for nearly a year. Finally gave up on the idle problem (oscillation between 1500 and say 200) and thought well at least I can cure the stalling problem when pulling up to a stop by putting in the VSS. That installation cured both problems! I changed absolutely nothing else. Been running that way for around 1200 miles in three states. This thing runs as good or better than my new truck. FYI just short of 15 mph pushing a brick through the air.

Keep that VSS in mind especially with the auto computers. BTW mine is a C3W, I believe.