So the hundreds of part numbers for the 3-wire sensors is just a scam? Man, that's irritating!!! I just bought a universal one for the Box at $90 because the one with the plug is $170, but not opened yet so it's going back tomorrow.

So they all put out the same mV range too or does it matter?

Thanks!

 

I never mentioned anything about the 2 wire O2s. Yes, the 2 wired ones are different than the 1 and 3 because it is gronded by the second wire and not the body of the sensor. However this can also be retro fited just like a 1 wire to a 3 wire system. As long an O2 sensor only has one SIGNAL wire it can be retro fited into any 1, 2 and 3 wire system and it will work flawlessly.

1 and 3 wire O2 are easily interchangable. The heater element is not necesary to get a good reading. It's only there to heat up the O2 before the exhaust can. Creating lower emmisions while the engine is cold. Once the engine is warm the heater is turned off. The 3 wires O2 was created to meet stricter new vehicle emissions laws. New wehicles get rated at cold start up emmissions and warm start emissions. The Heater was implemented to get the O2 up to operating speed as soon as possible to meet the cold emission limits. In a way, it's like a block heater.

Do a little more search on other forums (Honda, VW, etc) and you will find the same info that I stated above. Of course Bosch will not tell you that the 1 wire is esentially the same as the 3, and they can be retro fited. The one wire O2 are usually between $10-$30, while the 3 wire start at $40 and go up.

 

It's not really a scam, but rather the cost of making all the different conectors and lenght of wires including the necesarry clips and wire mounting tabs for each individual model of vehicle. The higher the production the cheaper the part. For example the 3 wire for a Honda Civic is under $100usd, while the Boxter is, as you stated, $170. The lowest cost for Bosch to make O2s is to make them in large numbers and the universal kits are a prime example.

 

If you read Bosch's site that Garth linked, Bosch does say that. They're all really interchangable 1, 2, 3, and 4 wires. For a heated o2, the 4th wire is listed as 'optional' in their heated O2 sensor installation instructions. You just ground it somewhere like the 2nd wire on a 2 wire.

I have a 928 specific question. Euros do not come with O2 sensors since they are permanently open loop. 84 US cars have O2 heater powered from the L-jet relay. 85 US has the O2 heater powered from the fuel pump relay. The fuel pump seems like the better idea. Is there a reason (fuse or relay) to power it from one over the other? I'm going to be using the 4-wire for a 2000 2.0 Jetta OEM ($22.99 from NAPA).

 

The easiest setup for you would be to use a single wire O2. They are around $10 and there is no need to ground anything at all. If you gound a 4 wire it will act like a 3 wire o2, right? Since the heater wires in a 3 wire O2 are pretty much useless, why not just go with a single wire O2. This way you don't have to run a relay or extra wires for the O2. It will be a simple, effective way to set this up.

 

Sorry, I was unclear in what I think is the "scam". I know it's not a scam, just taking advantage of the average knowledge of people. I get the additional cost of different connectors and mass production, but if there are no connectors on the universal they should cost the same to produce.

Thanks for the info Imo! I'm off to eBay for Boxster sensors. This is awesome!!

 

My O2 sensor bung is halfway out the Y-pipe after the headers. I'll be using this for an air/fuel meter, so I'd like it to be accurate. With it that far back, it may not get hot enough without the heater. At $22.99 vs $10-ish (I haven't found them for much under $20), that's not much of a price increase for improved performance.

 

The stock O2 locations for the 928 is also pretty far from the exhaust manifold. They are righ between the two catalytic converters past the shifter handle. If your Y pipe is a replacement from the big 3, the O2 sensor location would be same as on the stock Y-pipe. I know this cause we replaced the stock Y-pipe on my brother's '83 928 a few years ago and the O2 sensor location was identical.

The heater is only designed to work for a pre set time period, it's not supposed to be on all the time. If you keep it on all the time, the heater will burn out really fast. I have an A/F gague spliced into the stock O2 in my '85 928 and the signal is still pretty weak until the exhaust warms up the sensor.

My suggestion to use a single wire o2 was not price dirven. Keeping things simple is always better than over engineering. After all, for no apperant reason, Porsche did alot of over engineering on the 928.

 

I thought the heater only ran at startup. Looking at the wiring diagrams, the stock 3 wire sensor on 928s is always on when either the injection computer or fuel pump is on (depending on year). I also found references on the internet to wiring them into headlight or fan circuits that always have power.

 

Hmm, interesting. It's possible that you are right, it's just doesn't make sence to have the heater on all the time. The heater was supposed to heat the O2 until the exhaust gases reach operating temperature. It's possible I'm mistakem when it comes to O2 heaters, not like hasen't happened before.

If your Y-pipe different than the "off-raod" ones available from the big 3?

 

It's a custom 3.5" Y coming off MSDS headers.

Maybe the O2 sensor self regualtes the heater somehow. As it heats up resistance goes up so less current flows so it heats less... or something like that.