o2 sensor always reads 0

[auto alchemist]

this is on my 93 5.0 HO

ok, i had an o2 sensor that was reading 0 all the time so i figured the o2 sensors needed replaced, so i replaced them and ive still been getting horrible mpg, so i started replacing a bunch of stuff, long story short, i put it on the scan tool today and the #1 o2 sensor is reading 0 and its the new one, but it was the same side as last time, what could be wrong?

im thinking maybe a bad ground?

[Rick93coupe]

You probably have a bad harness. I'd pull the harness and check for continuity on each of the wires.

[auto alchemist]

You probably have a bad harness. I'd pull the harness and check for continuity on each of the wires.

would a mustang harness with MAF be the same as a tbird 5.0 harness?

and coul i just use the engine bay harness the plugs in near the firewall or would i need the harness that goes under the dash also?

[Rick93coupe]

would a mustang harness with MAF be the same as a tbird 5.0 harness?

and coul i just use the engine bay harness the plugs in near the firewall or would i need the harness that goes under the dash also?

That I'm not sure of. Do you have a mustang or a T-bird? Either way, I would unplug the harness from the O2 sensor and where it meets under the hood and check there first.

[quik lx]

Check the wire between the #1 (I assume Right?) O2 sensor. It's a green wire with a pink tracer at the EEC computer (pin 29). on the O2 harness connector one wire will read to ground and one will be 12VDC. You want the other one, you should have continuity between the connectors. There is also a connection at left side of the engine bay (looking at the engine) for the O2 harness to connect to the EEC harness. It gets burnt on headers alot. If your O2 harness is bad, The Detail Zone sells a whole new harness for around 60 bux.

Once you figure out your O2 problem, change the EEC's coolant temp sensor (not the one for the temp gauge) and the EEC's Air temp sensor (both in lower intake). These sensors are 15 plus years old usually and get overlooked all the time.They provide information for fuel ratio/scheduling to the EEC.

The Engine coolant temp sensor leans out the mixture at certain times to shorten the time it takes to warm up the engine helping you get good gas mileage, while the Air charge temp sensor monitors incoming air temp to set fuel ration for good performance.

I picked up a few more MPG doing this. Our hatch gets around 22MPG on the highway with mods.

Also check the vacuum line to your MAP sensor, if the line is kinked the computer cant calibrate for engine load. Its signal affects air/fuel ratio, ignition timing and altitude compensation.

Hope this helps. Good luck

[auto alchemist]

i already replaced all of those sensors, here is my other thread http://www.stangbangerz.com/forums/showthread.php?t=40113

yes i have a thunderbird, and about the wires, my o2 sensors are 4 wire heated o2 sensors, and im not sure but i was thinking number one was the driver side, my tbirds a 93 so it has a MAF, and it has been replaced already, but i actually know it was bad when i bought the car

but see the weirdest part about it is in the summer time i was getting 22mpg, and thats in a big heavy automatic tbird, but then my mpg seemed to drop consistantly with the temperature change.

does anyone know of the tbird harness and the mustang harness are the same? this is my dd right now and untill i get my other car finished i cant have this car down for more than a few hours.

[auto alchemist]

ok i found my manual, there 4 wire o2 sensors, and bye looking at my wiring diagram, 2 of the wires are shared with the other sensor among other sensors, so im thinking i should check the wires that are only used on that sensor which are

tan/orange= which only goes to the ecu

black and green= ground wire