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tail pipe with oxygen sonde for FI bus will it work?
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05gh
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PostPosted: Fri Jun 15, 2018 2:54 pm    Post subject: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

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The california heaterbox and catalist has been replaced by standard heaterbox and mufler. And now I want to relocate the oxygen sensor as show on foto.
I will use a 4 wire oxygen sensor with heat element to be sure that the operating temperature will be 600 F. Has anywhone done this before and will it work?
The reason why I'm doing this is tot get a beter fuel/miles. When you let out the oxygen sonde, the ECU will use a default rich mixture.
The motor has code GE, and it is a 2liter injection with oxygen sonde. This is a one year only CA bus (1979).
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raygreenwood
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PostPosted: Fri Jun 15, 2018 3:06 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

That is q very poor place for an 02 sensor. The tail pipe...and for soke diatance back into tue muffler....has TONS of oxygen contamination from turbulence and sucj back into tue pipe. Ray
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busdaddy
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PostPosted: Fri Jun 15, 2018 3:25 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

Fat thumbs Ray?, you shouldn't text while driving Razz

What Ray was trying to say before autocorrect jumbled it is that location is a bad idea, too much outside air mixing in will skew the readings. The other end of the muffler is a better choice.
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05gh
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PostPosted: Fri Jun 15, 2018 3:59 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

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Yes it makes more sense the pleace the oxygen sensor in front but the mufler is bolted directly on the heaterboxes
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Tcash
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PostPosted: Fri Jun 15, 2018 4:44 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

On the tail pipe you will get false air, which will drive your mixture rich.

If you could do something like this, it would be better. Or tap into the heat exchanger.
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PostPosted: Fri Jun 15, 2018 5:27 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

Tcash wrote:
On the tail pipe you will get false air, which will drive your mixture rich.

If you could do something like this, it would be better. Or tap into the heat exchanger.
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Or also on my bus is a bung further upstream... it only gets one bank of cylinders but even less chance of contaminated air....

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Tcash
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PostPosted: Fri Jun 15, 2018 6:35 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

aerosurfer wrote:

.Or also on my bus is a bung further upstream... it only gets one bank of cylinders but even less chance of contaminated air....


I wasn't going to throw you under the bus, but you outed yourself. The pick is of your bus.
So you moved the o2 upstream, did that drive your readings richer?

Get ready for the onslaught, of your missing an exh hanger bolt.

Thank you
Tcash
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raygreenwood
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PostPosted: Fri Jun 15, 2018 6:46 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

busdaddy wrote:
Fat thumbs Ray?, you shouldn't text while driving Razz

What Ray was trying to say before autocorrect jumbled it is that location is a bad idea, too much outside air mixing in will skew the readings. The other end of the muffler is a better choice.


Yeth....thas whuth wuz I wut crying to thay.......be vewy qwiet.....its texting season!

Way
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raygreenwood
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PostPosted: Sat Jun 16, 2018 7:32 am    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

Ok....now that I am in less of a hurry......a couple of items. If you want the readings of your wide band 02 sensor to actually be reasonably close to accurate.....and not have off again/ on again mysterious readings that cause you first to have to interpret or interpolate based on how you are driving at the time.......there are several places you do NOT want to place the sensor. The first....we have already mentioned and will just gloss over it again.

1. As mentioned.....do not put it close to the tail pipe. It will have wildly varying readings at most rpm ranges except steady throttle at high rpm like highway speeds where there will be enough exhaust force to prevent back flow. This is why for years before OBD-2 the sond that was used by emissions testing shops....were an average of 36" long flexible stainless that could get as far as possible from the tail pipe. These still caused problems in strange mufflers like ours......because a shop could never tell exactly where the probe really was unless they were experienced with VW and knew what was going on inside of the standard muffler.

2. Do not put it in one manifold side. There is too much odd variation in batch fired injection systems at low rpms....unless you pick the perfect cylinder that has the best overlap of iniection to open valve port. Also its quite common in old systems like ours....which are far less efficient than modern injection systems....that there is a LOT of unburned fuel in the exhaust just downstream of the valve. It can cause you to see richness that is not really there....combustion wise...and assume the system is running richer than it actually is.
You can get alternate rich/lean variation below about 2000 rpm.

You want to find a location to sample the confluence of all four cylinders as much as possible.

3. While putting the sensor in the end opposite of the tailpipe on the standard muffler is MUCH better than in the tail pipe as Busdaddy noted......it also has its own issues.

The way the standard muffler is laid out you can still tend to get mostly gases from one cylinder pair. Also....in the end opposite the tail pipe is "usually" a resonator chamber that while it does get a good amount of gas change over.....because it finally dumps into the final tail pipe here..... It also acts as a pressure/compression chamber......and putting the probe right in the end may put it in kind of a dead area. If putting the probe in this end works best for wiring etc......I would put it in the rearsard side of the muffler as close as possible to the entrance to the final tail pipe.

Take a look at the section of an Ernst muffler. I have a brand new Dansk I have been thinking anout sectioning to see if there are any REAL differences in layout.

https://www.thesamba.com/vw/forum/viewtopic.php?t=653839&highlight=ernst

There is also a place....dead center in the muffler where both cylinder banks dump into the muffler body and mix....before they move toward the left end exit chamber. I would say this is the most balanced location to put the probe.

That would be just aft of the oil pump and toward the bottom of the muffler. Ray
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05gh
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PostPosted: Sat Jun 16, 2018 3:00 pm    Post subject: Re: tail pipe with oxygen sonde for FI bus will it work? Reply with quote

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Thanks @Ray, great artical I'm beginning to understand that placing the oxygen sonde in the tail pipe is not a good idea.
Thats massive CA 1979 exhaust thing (see foto) on the left side of the car is replaced by a heaterbox and the ERNST mufler.
The PO has tweakt the AFM for a certain (I gues rich) level oxygen/feul mixture.
The car speeds up easily and has a good torque .
The down side is low gas miles and in case off rich mixture the oil get contaminaded. And as result of that the rubber seals will dry out and starting to leak.
So I have 2 options leave as is or weld the oxygen bung in the middle of the mufler.
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