Rob Edwards

So despite all the records on this car going back 17 years, there's no evidence the O2 sensor has ever been replaced. So it's time.

I'm sure there's a magic combination of keywords that would lead me to a R&R protocol for dummies, but I can't find it, and it's probably so obvious that it's not even in the WSM. I've also been under the car for many hours but never looked at the exhuast critically before, so here goes with the idiot questions:

Do I have to drop the exhaust from the back of the headers to get at the 02 sensor? (I assume so, but have not seen this described for 87+ cars)

I assume you only need to undo the front, and the cats and the resonators sort of bend down enough to get at the sensor?

If so, do I need new exhaust flange gaskets and nuts? Are the bolts thru the flange integral or are the old ones ok if not too rusty?


Will my universal 22mm O2 sensor socket work on the 928 sensor?


I know this schtuff should be obvious!

RyanPerrella

Yes you have to drop the exhaust

the front should be adequite, the rear will drop and flex where you can get it off. Although you may need to put so much torque on the sensor to break it loose, that a now dangling cat will be hard to hold tight to get torque into the sensor itself and not pushing the h-pipe/cap in the other direction. So worse case scenario you pull the entire cat and put it on the floor. Its easier to reinstall and properly torque the sensor with the cat on the floor anyway. Although its a pain to seperate the ends of the cats from the mid mufflers even when the band clamp is off. They tend to stay rusted together to a degree.

22mm or whatever size it is will work.

Gaskets should be replaced, nuts should also be replaced as well as bolts but you can get away without doing the nuts or bolts. I would replace the $16.00 gaskets though regardless.

The bolts are expensive i think to replace the bolts and nuts it came out to something like $30-$40. I wasnt interested in doing that for what it was. I put those off and was just going to get metric nuts and bolts at a fastener store but never got around to it. I cleaned up the bolts with a wire wheel and they work just fine.

RyanPerrella

did you buy the 928 specific O2 sensor or the "whatever was on sale" version?

Guess it dosent matter, but when i replaced my O2 and i spliced the wires i used butt connectors and did NOT solder them. Bosch dosent reccoment soildering them for some reason. I know nothing about electronics so i wont even guess as to why.

Rob Edwards

Ryan-

Groovy, thanks. I ordered the 928-specific sensor. My soldering skills are poor. Perfect excuse to buy some parts and listen to some music in the garage......

RyanPerrella

yeah i need to drop my cats to get the clutch lower cover off and track down an oil leak. Last time i drove the car i heard popping noise of oil landing on the hot cat and going snap crackle pop.

Mrmerlin

Hey Rob before you drop the exhaust open the CE panel and disconnect the O2 sensor wires they are fitted about 2 inches aft of the CE panel on the trans hump push the wires through the hole along with the rubber grommet so when you drop the front pipes you wont shear them off . After this remove the right front heat shield it is just above the right manifold to head pipe connection, Its also a good idea to replace the flange connector bolts as they are usually rusted and may have to be cut off to remove them, dont forget to lossen the 2, 19 mm bell housing bolts that hold the manifold mounts these will let the header pipes drop , The O2 sensor is located in the center top of the header/cat pipes so it may take a bit of manuvering to get to the O2 sensor, add some anti seize to the threads of the O2 sensor screw it back in and then feed the wires up through the hole in the body crossmember , then feed the wire through the side of the tunnel and fit the grommet , then reconnect the manifolds, then the wires in the CE panel then the heat shiled as you may have to fiddle with the wires a bit for fitment, usually the exhaust gaskets can be reused, but thats your call. Make sure to use anti seize on the manifold connector bolts so the next SOB, wont have to fight them to remove them. Good luck

dr bob

Rob-- Please save the old sensor for me. I'd like to salvage the connector from it and attach it to a generic Bosch item as a spare. It's a bit easier doing the splice on the bench.

The gaskets should be repolaced, but... You may want to go to your POLAPS and find them generic. I'm also very tempted to put stainless in the flange bolts and nuts. No matter what, you'll want a dab of anti-seize on the threads. There's a support tab on the flange that attaches to the bellhousing, another place to demo your artistic skills with the anti-seize brush.

The wire snakes through a grommet that high on the tunnel on the pass side. Carpet gets lifted after the carpeted side cover is off the center console, and you can see the wire and the grommet. I hope the new sensor has a new grommet already included on the wire.

In spite of the Bosch warning about soldering the wires, I did it and it works fine so far. The conductors are plated with something, and they may not be copper inside because of the heat and vibration they endure. Steel or maybe SS? Anyway, they soldered OK with a little prep. Butt connectors just don't give me that warm fuzzy this-is-going-to-last feeling.

Imo000

Since you are dropping the exhaust, do yourself a favour and remove the two rear lower bell housing bolts then replace them with a couple shorter one. Next time when you need to remove the lower bell hosing, it will come off without the need to remove the exhaust. The stock length rear bolts are too long to clear the exhaust. To check the crank end play and to loosen the torque tube coupler, the lower bell housing needs to come off. On auto trans 928s this is a routine maintenance item.

Garth S

One of the reasons why Bosch sell their generic sensors with crimp connections is that they claim the reference atmospheric oxygen concentration against which the exhaust stream is compared derives from a miniscule flow of air aspirated/drawn through the sensor output wire via the in car connector.

No, I did not make that up ... however, if true, then any break in the insulation jacket on the sensor side of the wire would do, regardless of how the ends are connected.

Giovanni

You do not have to drop the exhaust to remove the o2 sensor. You just have to get the perfect position to remove it and an open wrench. Did I say it was a bee-hay-tch to remove it with the exhaust in place?

Imo000

I’ve read the same thing on Bosch’s site but it makes absolutely no sense to me. Oxygen molecules traveling on the inside of an electrical wire?!?!?!?!

Z

Take a piece of the wire from an old sensor, put one end in a glass of water, and blow in the other end. You'll see bubbles. When the connection is soldered, molten solder will wick up into the wire underneather the insulation, and block that flow path.

dr bob

Probably explains why they didn't use copper-- drawing oxygen through that would cause the electrons to fall off the wire! With all due respect to the Bosch claim, why wouldn't they just use ambient air as the reference for the measurement? Looking at the sensor it might make more sense to scare amateur solderers away, and also to avoid a possible galvanic junction that would affect the output if the joint wasn't mechanically sound before solder was added.

Anybody remember Rudy Galvanni? Stacked a few coins together, ran them under water, made enough of a current to make a frog's leg twitch. Scared the hell out of the wife one night when her dinner jumped right off the plate as he poured her water glass.

Imo000

Can’t you do that with just about any multi strand wire? Wouldn’t it be easier for Bosch to just design the sensor that has a long air tube? Also once it reached the connector by the EC panel, what happens to these magical oxygen molecules? I don’t remember seeing any oxygen molecule sensing device by the CE panel.

I think Bob is onto something here. It’s more of a deterrent that anything else.

Z

They are using ambient air as the reference. They're getting it through the wire. Bosch says soldering the sensor wire is okay, as long as there's a crimped or mechanical connection in the sensor wire between the sensor and the soldered joint. If a galvanic junction or possible poor soldering technique were their concerns, they wouldn't say it's okay to solder further up past the crimped connection.

They did. It's commonly refered to as the wire.