I'm replacing the O2 sensor, and it's the one on the passenger side, above the exhaust in a position that's hard to get a wrench on fully. The wrench I am using is 7/8 but it seems a little too big - but nothing else seems to fit.

I've sprayed PB blaster. I'd try heat, except that I can't really access the area well.

I'd also love to know how to unplug the plug. I tried lifing what I thought was a tab, and ended up breaking it. But the thing still won't come loose.

I'm sure this is quite easy once you know. I've replaced O2 sensors on other vehicles, but the access to this one is a real PITA.

Thanks!

 

Since you’re replacing it, easiest way is to smash the head off with a hammer and then put a socket on. If you’ve broken the locking tab, push the connectors in and out until it pulls apart. You can buy the O2 socket at any part store. Heat is very beneficial to get it loose.

 

Just removed the most stubborn O2 I have ever encountered. This one mounted down at the Y pipe.

Tried the O2 socket, the kind you borrow at the big box auto parts. No dice. I could see the socket was just splaying out and going to round off the sensor nut.
I put a hose clamp around the socket to reenforce it. nope.
Tried a boxed end combo. Nope. Not enough leverage and it had the round off feel to it. Pinched a nerve doing this and quit.
Two weeks later I cut the sensor off at the nut. Six point impact socket and 24" Snap on breaker bar. Nope.
Heated the bung with a propane torch. Nope.
Wheeled out the oxy acetylene torch and got the bung really hot. Felt movement, thought I had it. Nope.
She broke off flush with the bung.
In a brain fart moment, I thought I would just wash the remains out with the torch. Nope, it's stainless steel.
Got the remains hot and tried a couple easy outs. Nope.
Got out my die grinder with a 1/4" bit (like a Dremel) and ground one spot until I saw bung threads.
Got the remains hot and tried the easy outs again. Nope.
Picked at the red hot remains with a pointed punch and got it loose in the bung.
Couldn't get purchase to pull it out so I just punched it into the pipe.
Went to O'Reilly's and got a Lisle brand thread chaser for about $9. It cleaned the bung up plenty good to install a new sensor but the tool itself is beat to death. I'd recommend another brand.

Best part of saga is the new sensor fixed the truck!

 

I tried 4ft bar and it didn’t help, heated it with map gas for about a minute after breaking head off and M12 1/2” impact broke it loose on mine. I would have given up on yours and just made a new hole haha!

 

O2 sensors are 22mm. The only one I could not get off was on my Ford. I just welded in a new bung. Simple easy. Yes, I left the other one there.

If I get a stubborn one, I cut the cable off and use a wrench. Cheap O2 sensor tools will flex, they tend to look as good as one that is 4x the price, but it's just another way the Chinese has screwed us again. If you can't afford a good one, don't waste your money on a cheap one.

The O2 sensor has a seal so there is no amount of penetrating oil that will pass that seal. I think penetrating oil is a total waste of time unless there is already some movement. I am not convinced that the stuff can penetrate anything in the time I got to fix things. If the hardware does move, then the oil can work into the threads. If it is locked up tight, heat is your friend.

 

The best 5 tools I ever bought, for stuburn nuts/bolts.

 

Penetrating oil and exhaust heat was enough to get mine out. Maybe a couple gentle taps from an impact could help motivate yours to get moving.

Oxy-acetylene is essentially an eviction notice being placed by a bulldozer.

 

I took my exhaust off, had it in the back of a truck, and used a 5' bar with a torch while I stood on it. It worked.

 

Didn’t use this on O2 sensor, but I’ve used my floor jack to push the ratchet up when I wasn’t strong enough with suspension bolts. Something gives one way or another!

 

Congrats on fixing your truck! I actually got mine off, using a removal tool from NAPA and a breaker bar, and Kroil, and PB blaster. But your post raises as many questions as it answers. Here they are:

You seem to imply that there is another O2 sensor on your truck. I thought these (mine is a 96 5.8) had only one. Can you tell me where the other is located?

The next question is: did your new sensor come with a wire long enough to reach the old pigtail? Mine, it seems, does not. So I have to decide if I'm going to splice into the brand new sensor with the old pigtail.

 

My 1995 California 5.0 has only one O2 sensor. I only noted the location because my 1986 truck has the sensor on the passenger side exhaust manifold.
The Bosch brand O2 sensor had the same length pigtail as the original so it was perfect length.

 

My 95 F250 5.8 has two O2 sensors.

 

This implies that you have two, the other would be on the drivers side.
If you only have one, should be in the center of the Y-pipe.

 

missing (1) tool. My bfh.

 

Why didn't I think of that? That'll work great on a 30 year old o2 sensor and exhaust pipe.