Cutting the O2 sensor wire...

[travis]

'84 Mercury Cougar with a CFI 302/AOD/2.73 gear combo, currently bone stock with 90k miles.

I've been back and forth on this project for quite some time, the car is so nice and stock and cush I almost hate to start modifying it. But it is also horribly gutless so I have to do something.

Ripped off the stock exhaust system tonight, and found 1 major cause of the lack of power. The exhaust consisted of 1 7/8" outlet manifolds, into dual cats, then y'd into a single 2.5" outlet. From there it stepped down to a 2" pipe, and then stepped down again into a single 1 1/2" in/out aftermarket turbo muffler, then stepped back up to a single 1 7/8" tailpipe. WTF lol

I've got a pair of shorty headers and a fox body 2 1/2" dual exhaust system with an H-pipe to install tomorrow. I was going to try to run this with the otherwise stock engine, but I had to cut the wire to the O2 sensor because I couldn't get the sensor out of the original manifold (nowhere near enough room to get any leverage on it, not enough room to get the connector apart either).

What is going to happen if I try to run it with no O2 sensor? I wanted to try it out with the CFI system to see how it would run with the mucho better breathing exhaust, but am now wondering if I kind of shot myself in the foot here.

Fwiw, I've got a 2bbl motorcraft carb and an aftermarket ignition system that I planned on adding in the future, just wasn't ready to install them yet because I will need to make some changes to the fuel system.

Comparison of the removed muffler to one of the new 2 1/2" turbo mufflers...

IMG_20221204_204023_775.jpg

[Alaskaracer]

Without the o2 sensor, the ecm can't "see" the a/f mixture, so it can't adjust.....it will run a default fuel map instead, and will turn on a check engine light. Might run ok, might run like crap.....Sensors in those are reasonably cheap...won't take much to replace it, I would....

[mt-engines]

Without the o2 sensor, the ecm can't "see" the a/f mixture, so it can't adjust.....it will run a default fuel map instead, and will turn on a check engine light. Might run ok, might run like crap.....Sensors in those are reasonably cheap...won't take much to replace it, I would....

Narrowband o2 sensors don't really tell you the AFR. Kinda lets the computer know if its close.

Cruise might suck, but wide open throttle and cold start shouldn't be affected.

[mt-engines]

Without the o2 sensor, the ecm can't "see" the a/f mixture, so it can't adjust.....it will run a default fuel map instead, and will turn on a check engine light. Might run ok, might run like crap.....Sensors in those are reasonably cheap...won't take much to replace it, I would....

Just make sure its high up in the collector since it isn't self heating.

[mag2555]

Gut less you say?
With 90K on the odometer Without fail the first thing I would have is replace the timing chain and gears!

Just to have a base line I would run a cylinder pressure test before and after replacing the chain.

[Rick!]

The ECU (EEC IV, or EEK!) will not see the O2 sensor switching at an expected frequency so it will stay in open loop and eat more fuel. It should also run at a higher spark advance which will give the impression of better performance at the risk of more pinging.
If you want to mess around more, find a resistor that mimics a cold CTS and then use a DPDT switch to go from operating temp to "cold".
After everything you are doing, it will still be a toilet bowl throttle body with little holes in it with a base engine of a whopping 130hp.
Since port fuel injection didn't really come into the fore until 1986 with SEFI in the mustangs and pickups, it would maybe be better to swap in that type of system, along with 351W heads, a good cam, etc.

[travis]

Is there a "extender" to move the O2 sensor 12-16" down stream? Shorty headers really don't have a collector so I'm going to have to add a bung in the pipe. I'd planned on doing this anyway for an a/f monitor later when more serious mods happen.

A timing set, along with a cam swap, is planned...i already have those too. I'm not sure if or when Ford quit using those nylon covered aluminum timing gears on the 302. But...with only a factory rated 8.3 compression (probably closer to 8.0), I'm going to add some ported and milled E7TE'S if my damn valves ever show up...I ordered them almost 6 months ago. Plus I need to get some gears in it too. And probably a convertor too. And probably subframe connectors too...this thing feels pretty flimsy.

[V12MECH]

The single wire O2 sensor produces a 0 to 1 volt signal back to ecm. Napa has a universal deal with a long lead, NGK or Bosch ,or they used to, just do a nice solder or crimp with shrink tubing. They probably have a bung also.

[BLSTIC]

Without the o2 sensor, the ecm can't "see" the a/f mixture, so it can't adjust.....it will run a default fuel map instead, and will turn on a check engine light. Might run ok, might run like crap.....Sensors in those are reasonably cheap...won't take much to replace it, I would....

Just make sure its high up in the collector since it isn't self heating.

Any number of heated sensors are also an option. I powered a narrow-band sensor monitor from the O2 heater circuit on an old subaru and it only switched off with the ignition so I imagine that kind of circuit is fine.

Just gotta be close enough that there's not a lot of upstream condensation to ruin the party by hosing a hot sensor. As a bonus it will probably hit closed loop much earlier than stock and save some tiny amount of fuel/planet/money

[Schurkey]

My '88 K1500 came with a one-wire O2 sensor.

Bought an adapter harness, and a heated O2 sensor. Doesn't fall out of closed-loop at idle any more. If I were doing this again, I'd get a 3-wire harness and sensor instead of a 4-wire harness (and sensor), from the same company that sold me the 4-wire harness. In the end, I tied the two ground wires together anyway. And of course, this harness is for use with GM sensors/connectors; but perhaps they have Fordly stuff, too.

https://www.amazon.com/gp/product/B074F ... UTF8&psc=1

[travis]

I like the idea of a heated sensor...that would allow me to mount it in a more easily accessible location a bit further downstream.

On the heated sensors, are they powered all the time that the key is on, or do they cycle to maintain a certain temp, or is it only when everything is cold? I've got a couple of good O2 sensors from my '99 suburban. I'll have to check but I think they are also 0-1v...it would be easy enough to add key on power.

[BLSTIC]

I like the idea of a heated sensor...that would allow me to mount it in a more easily accessible location a bit further downstream.

On the heated sensors, are they powered all the time that the key is on, or do they cycle to maintain a certain temp, or is it only when everything is cold? I've got a couple of good O2 sensors from my '99 suburban. I'll have to check but I think they are also 0-1v...it would be easy enough to add key on power.

My previously mentioned Subaru O2 sensor was constantly heated and only about 6" away from the head-manifold flange, underneath heat shielding. It was turbocharged, but the turbo was a couple of feet away (ever wondered why early WRX were lag city? That was the short side, add another 2 feet of tubing for the long side...).

I'd say you could power it from ignition switched signal safely. If you do find yourself burning sensors it would be easy enough to add a vacuum or speed switch so it disengaged heating under high load.