My 86 XLT 302 EFI has been registered as "collector" here in Wisconsin and does not have to go through emission inspection as a result. I have decided to remove my failing catalytic converter with a Flowmaster resonator. The new resonator will force me to remove the existing emissions sensor that is just forward of the existing cat, and will make it a chore to put back in place. It can be done but it'll be pain, so prior to doing this I uncoupled the quick disconnect from the exhaust sensor to see if it would go into a fault condition on the dash, and it did not. Do I need it and if not what should I do with remaining lead?

After driving it for about 2 hours, it started to run extremely rough, and could barely idle, was this coincidental or did eliminating that sensor create this new problem?

Thanks for your input

 

It was not a coincidence. The ECU requires all of the sensors to be functional. And it doesn't always light a light, like more modern ones do, to tell you that it saw what you did. It just puts you in limp-home mode, which kills your power and economy.

You can check this out by pulling the codes, as described in the stickies.

 

The sensor you are removing is the O2 sensor (oxygen sensor) these old speed density systems need this sensor to operate properly to adjust the fuel air mix in the engine.
you NEED to keep in place this one is non optional. The truck will NEVER run right with out it.

 

Is there a way to bypass or trick the sensor?

 

Ok, got it. Now that it is in "limp home mode" how do I get it back?

 

Yes, and no. You could provide the right voltage to tell the ECU that the air/fuel ratio is perfect, and the system might not be smart enough to recognize that it never changes and throw a code. However, that won't give you the proper air/fuel ratio so the truck will still run poorly.

This one is non-negotiable. And it's placement is somewhat critical, meaning it has to be roughly where it was in the exhaust system originally.

 

Reconnect the sensor and drive it awhile.

 

Once again, thanks fellas

 

Isn't the O2 Sensor in the R-Exhaust manifold ?

 

Not in all applications and since the OP never bothered to post a pic and called it a sensor, the only sensor in the exhaust system is the O2 sensor.

 

Disconnect the battery then turn on the headlights then
turn off head lights reconnect battery, ECU is codes are cleared.

Turning the head lights on off with the battery disconnected with discharge any capacitors in the system that may be holding a charge preventing the ECU from clearing.

 

Also, you are going to have to take it for about a 10 mile ride before checking codes.

 

It won't throw a code the O2 sensor will be detected and present and responding to changes in fuel air mix and since it is not after the cat, the computer will have no idea the cat is missing..

He will see a reduction fuel mileage though as the removal of the cat will free up the exhaust and lean the engine out the ECU will respond by richening up the fuel air mix.

 

Well, that's what I was getting at, I believe the O2 is in the Exhaust Manifold, leave it connected, the ECA won't know the difference unless a Back-pressure change affects the exhaust gas composition, like you say....

 

I experimented with disconnecting the O2 sensor on my little ranger v6 (1986). On first start up it ran fine, and then about 5 minutes or so later it would always throw a fit and cough and stumble a little bit, and then take off and do fine after that. It did this each time I started it, sooner if it was warmed up already. I am assuming it was looking for the O2 sensor each time it threw a fit, and after about 5 seconds of looking for it, it would give up and just run on the computer memory. I ran it this way for awhile, the fuel mileage was way down running it like this. No use having fuel injection if it's going to be like this. I bought a new one.