All:

Hello. I need your help with replacing my O2 sensor in my 1986 Ford F-150 (302 EFI).
I think that the truck is running rich - bad gas mileage, slight odor from the tail pipes, soot on the tail gate and the mechanic who worked on it last (replacing the catalytic converter) said that inside the exhaust pipes look like a dirty chimney. (I did have codes on the OBD1 about the O2 sensor). The engine has 151K on the odometer and I do think that the O2 is original from 1986. The O2 is probably the last thing that would need to be changed. Since April there has been a new MAP, new TFI, distributer (cracked), spark plug and wires put into her.

Anyway....

I have a pit in my garage so I can look up under the truck. I have found the O2 sensor and I have found the clip on the other end of the single wire. My problem is that I do not have 9-foot arms to reach the clip as it is located at the back of the engine by the firewall.
How the heck do you get to this to unclip/clip it? I have no clue. Does anyone have any tips/recommendations - anything - that can help me accomplish this task? Any tips about getting the sensor out off the manifold? Any special tools needed, or "do this" or "definitely don't do this"?

Here are some photos.


I had a hard time getting my phone to take this picture. It's tight up in there. How do I unclip/clip a new sensor way back here?



I think that this is the original O2 from 1986. Any tips on getting this out?

 

If i remember correctly i was able to reach mine from the engine bay. Also, they make o2 sensor sockets, they have a cut out in the side so the socket can drop over the wire. I thought mine went and when i tried to swap it out, i couldnt get the thing out, even after soaking many times in pb blast and hitting with a torch. Hopefully doing the same will work for you. Thankfully my problem was not the o2 sensor so i let mine be.

 

You can cut the wire on the old sensor, and then pull the harness up to where you can unclip the old wire. And that also lets you use a regular socket or wrench on it. Of course you will need the special socket to install the new one unless you can get a wrench on it to tighten it up. The sensors use sparkplug threads if you need to buy a thread chaser to clean the threads in the manifold.

 

All I can say is good luck! I've got an 85, same setup as you, and the only way I can see to get it done is pull the damn header off. I was able to use a long grabber to snag the harness from above and get the connector pulled which at least allowed me to test it. But even with an O2 sensor socket there was no way possible that I could find to get enough leverage on it to get it out. The issue I'm having is liveable for now so when I upgrade the headers and exhaust I'm going to relocate the sensor down to an H- pipe. If you figure it out please share!

 

Here you go, Laser Tools #6098:






I’ve got one and it is slicker than Bill Clinton under oath. Never had it let me down yet.

 

The one I bought is a very similar design. In fact I don't think the one you have would even get into the space due to the hook behind the 3/8" drive. The tool isn't the issue, it's the location of the sensor.

 

I just did an O2 sensor swap on my '86 5.0. I used this setup. The socket is a loaner from Auto Zone. That is a long handled 1/2" drive, extension and u-joint with a 1/2"x3/8" adapter to the 3/8" drive socket.

Be aware of where you are cutting the wire. Many replacements only come with about 5" of wire and require you to reuse the old wire connector.

Where the blue heat shrink tubing is is all the wire Bosch gives. And the original connector tends to be corroded so plan on cleaning it up.

On reaching the connector, I am six feet, three. I climbed up and knelt on the radiator support. Get the air box out of your way too. As for releasing the two tabs on the connector, I stuck the ice pick tool under one side and flicked the opposite side free with a medium flat blade screwdriver. It may be more difficult for you to separate if it is corroded. If so, I wouldn't hesitate to snip it off and hard wire it. I used dielectric grease under the heat shrink tubing.

The sensor has straight threads and a metal sealing washer just like a spark plugs. I second the idea of chasing the threads with a spark plugs thread chaser. You can then easily screw in the new sensor all the way by hand and needing only a eighth to a quarter turn to tighten.

 

I like that socket, that might get it done on mine.

Is the 86 that much different from the 85? Are we all talking EFI 302's? My air box is on the driver's side, O2 sensor is on the back of the passenger side header. For me the biggest obstacles were the heater core housing and the firewall trying to do it from above.

 

Is there a way to test an installed O2 sensor with reasonable accuracy? Maybe resistance or something like that? My experience with stuff like that, I'd spend 4 hours skinning knuckles getting the &@$ thing replaced, only to find out the old one worked perfectly. I'm a huge fan of periodic or preventive maintenance but I'd want to know that thing is defective first, because it's such a beeyotch.

 

Do a quick Google search but essentially you test the voltage to verify that it's in range. I suspect mine is a little slow to come up to the right voltage which is causing a small dip in my idle right after starting it warm. A small amount of throttle gets me passed the issue so I decided to just put the O2 sensor off for now.

 

In theory, yes, an O2 sensor can be tested. On a practical level? Not so much, especially for the home mechanic.

Early oxygen sensors are a simple rich/lean indicator. The output is a certain voltage (0.7?) above the ideal point, and less voltage below that point. These sensors have no way of indicating how far above or below, only that’s it’s high or low.

in a perfect world, the exhaust mix is hovering close to the ideal point. If the O2 sensor says it’s slightly rich, the computer trims back the fuel until the sensor says it’s lean. Fuel is then added until the exhaust is rich again, and the cycle repeats. Ideally, the mix is rapidly cycling slightly above and below the desired point, to average out as ideal.

As a sensor ages, the switching point usually stays fairly accurate. This part isn’t easy to verify anyway, as you’d need a professional level tailpipe sniffer to check the calibration. Plus, you’d need to get a sample before the cat, not after, where the exhaust has been cleaned up.

The aspect that usually goes bad is the switching rate. An old sensor can’t react as quickly as a new one. The rich/lean swings become more pronounced, as the sensor can’t react quickly enough to tell the computer what to do. The switching rate can be monitored with an oscilloscope (or a good multimeter with a hz setting), but what is considered good? How often should the sensor be switching high and low? Unless you’ve got a known good sensor for comparison, it’s all guesswork to interpret the data from the oscilloscope.

Most computer systems will eventually flag a problem if a sensor appears out of limits. However, it won’t always directly fault a bad sensor. You might get a code for rich or lean, but there are many other components that can cause the same symptoms (air leaks, wrong fuel pressure, etc.) If an O2 sensor is totally dead, that will trip a specific code, but that is pretty rare. The typical failure is a slow decline in the switching rate.

Later model vehicles are much better as detecting faults like that. 1986? Not so much...

So what’s a guy to do, short of acquiring $10,000 worth of laboratory equipment to test a $30 part? Treat the O2 sensor as an expendable part like spark plugs, distributor cap/rotor, fuel filter, etc. Spring for the $30 on a schedule instead of imagining an important part with a finite life will somehow magically last forever.

So on a practical level, Install the new one and confirm it’s hopefully good by seeing how well the engine runs and if any fault codes are generated. And it’s definitely worth buying a quality brand, not some cut rate no-name.

 

Another problem with testing the O2; Is the O2 sensor lying or really telling the truth? If it's not switching back and forth, it may be because there is something wrong with the engine. Or it could be a faulty O2 sensor. That can be a problem with feedback loop systems like this. One thing affects the whole system and the whole system reacts to it.

 

Hot dog! This setup here got it done for me today so thanks for posting up this picture. I had the sensor socket with the offset 3/8" attachment but just couldn't get a bite on the sensor. This style socket, which I didn't know existed, got the job done. Got the new sensor in and although it didn't fix the problem I'm chasing the truck does run noticeably better.