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DLK DLK is offline
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Join Date: Sep 2016
Location: Scheveningen (Holland)
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What to do with the O2 sensor, cat delete (3.2)

Hello all,

Recently I bought a 1987 3.2 Targa and had it shipped to Europe. First delivery of the car was in the US and it has the 930.25 engine (lower c/r than the euro engine) with a catalytic convertor and a Oxygen sensor before the catalytic convertor.

I want to delete the cat and fit the standard normal Euro muffler. I have bought an original Bischoff muffler to fit to the car. This muffler comes without a bung to fit the Oxygen sensor.

When fitting the muffler I will also add a Steve Wong chip.

Now, what would you recommend?

1) get a bung welded in the muffler and retain the O2 sensor
2) unplug and forget about the O2 sensor

I will ask Steve Wong if the can remove the O2 sensor from the ECU, not sure about that :-)
Old 07-19-2018, 01:10 PM
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The Mighty Pieholio
 
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Join Date: Nov 2007
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I see no downside to keeping the O2 sensor in the system.

It works at idle and when you are cruising. Wide open throttle it has no impact.

It will save money on petrol, also.
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1981 911SC Targa

Last edited by Bob Kontak; 07-19-2018 at 01:24 PM..
Old 07-19-2018, 01:22 PM
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Just do what I did, unplug it and forget about it. The car never changed characteristics at all. I have a wideband 02 with AFR logger installed and the car ran perfectly fine. And yes, Steve should be able to create a tune for your new exhaust setup without an 02 sensor.

Bob,
I ran mine with and without and the mileage was close enough that it could have been wind direction that changed it.
Old 07-19-2018, 03:13 PM
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Keep the 02. It will save you gas and provide a much smoother running engine at idle and part throttle. Once you break the 35 degree switch on the throttle body, it goes into open loop and has no effect on wot performance.
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fully disassembled, blasted, customized and restored 75 targa with factory hard top, 993 style turbo ft fenders, steel flares, C2 bumpers and rockers, 82 3.0 sc 9.5/1 engine with PMS flywheel, 964 cams, flowed heads, ssi's short geared 915 w/lsd, polybronze, bilstein,working lambda, modified and highly tuned cis, tensioners, pop valve, backdated exhaust and heater, 2300 lbs. no bolt left untouched. 1970 911E. Nice car but needs a re-do.
Old 07-19-2018, 05:42 PM
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Running too lean or rich can't be good in the long run.
I would keep it.
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Old 07-19-2018, 06:51 PM
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ASE Master Tech - 35 yrs
 
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i have 28-pin Wong chip in my '89 w/ headers, no CAT, sport muffler - Steve says "use the sensor" - said his chips do not "delete" the sensor circuit

in my case, i find the 91 octane wong chip for my setup to be on the ragged edge of wanting to "ping" under lower rpm load situations, esp on really hot SoCal days

- Steve suggested that i might have a "lean" condition - SO- i installed an AEM 02 meter w/ 2nd bung - it also has setting to allow use of the sensor with the gage, so you could get away with a single bung - I am not running lean!

thread on that http://forums.pelicanparts.com/porsche-911-technical-forum/895323-aem-wideband-o2-gauges.html

- local gas quality is a possible factor it seems - just keep the rpm a bit higher, eh?

(comparatively my 24-pin oem "-302 chip" will deliver 24 mpg with no sensor, & it pulls like a locomotove from low rpm with no pinging tendency) ( i have an extra DME)

i have not found that the sensor in-circuit has made any difference in the pinging tendency, but it seems it has maybe resulted in slightly better fuel economy (driving conditons vary - but 18 vs 24 mpg is the range i've experienced)

with sensor & wong chip i can see up to 24 mpg & get notably better midrange "ooomph"

see these
http://forums.pelicanparts.com/porsche-911-technical-forum/659959-steve-wong-chip-advice-10.html
http://forums.pelicanparts.com/porsche-911-technical-forum/581762-02-sensor-necessary.html
http://forums.pelicanparts.com/porsche-911-technical-forum/939680-gutted-catalytic-converter-my-3-2-still-need-o2-sensor.html
http://forums.pelicanparts.com/porsche-911-technical-forum/581762-02-sensor-necessary.html
http://forums.pelicanparts.com/porsche-911-technical-forum/924531-upgrade-dme-sw-chip-conundrum.html#post9231231

FR Wilke claims the 02 sensor is irrelevant - i have run his PowerProm chip, but it was 'way too aggressive on timing - terrible pinging even at light accel loads - likely was made for 93 octane vs the 91 i can get
https://www.google.com/search?q=PowerProm&ie=utf-8&oe=utf-8&client=firefox-b-1
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If it works, take it apart and find out Why.
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Old 07-19-2018, 08:44 PM
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DLK DLK is offline
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Just to follow up on this. I bought a used but very good condition Bischoff pre muffler and a friend of mine welded an O2 bung in one of the two pipes.

Yesterday I removed the old cat and found out that it was a universal cat that was welded to the existing front and rear section of the OEM cat. The diameter of the universal cat was a bit less than the original one and I think it was clogged up a bit.

The engine feels much smoother, a lot more torque when accelerating and it revs freely up to the red line. Also after a spirited drive the rear bumper isn't as hot as it was with the cat fitted.

Conclusion, my car really benefits from removal of the cat!

I have ordered the Steve Wong chip today and I am anxious to feel the difference that will make!
Old 08-15-2018, 02:32 PM
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