3.6 transplant -- how many O2 sensors?

[Deadeye]

Installing a 3.6 varioram into my 911. How many O2 sensors are needed if using the Motronic ECU? If any.

[CabMike]

I only have one on mine, but it is from a 964 not a varioram.

[Bill Verburg]

Originally Posted by Deadeye

Installing a 3.6 varioram into my 911. How many O2 sensors are needed if using the Motronic ECU? If any.

oe
all 964 and US '95 993 and all RoW n/a 993 use 1

US '96 -98 use 4

they will run w/ none, but not as well as with the correct one(s)

[mreid]

At least one, depending on your exhaust set up.

[Bill Verburg]

Originally Posted by mreid

At least one, depending on your exhaust set up.

using just 1 on a '96-97 is as bad as none. In a t/p you often don't care about dash warning lights so these will need at a minimum the 2 precat OBD sensors to prevent a limp home(default) situation. The 2 post cat sensors can be ignored except in places like Ca. were smog exams will mandate them

[Deadeye]

Exhaust will be 1-3/4" headers and MK muffler for quiet tracks and stinger exhaust for tracks without noise cops. So it seems if I use the Motronic ECU I should put one on each side? These two would be the pre- cat pair in the harness?

[Maltese Falcon]

Deadeye,
We put one o2 location on each collector, left and right .
The next pair of o2 sensors (light off cats) normally go after the precat....
absent with upgrade to headers.
If you plan to run two cats after the headers, have your muffler shop put two
O2 sensors after these cats.
This will eliminate check engine light/limp mode.
If not running cats anymore, have your ecu tech tune out the
C-E-L.
And for 1.75" headers, check out the U.S. Mfg. msdsinc.com part #
HO-911r , always available for Porsche enthusiast discount prices.

[Bill Verburg]

Originally Posted by Deadeye

Exhaust will be 1-3/4" headers and MK muffler for quiet tracks and stinger exhaust for tracks without noise cops. So it seems if I use the Motronic ECU I should put one on each side? These two would be the pre- cat pair in the harness?

It would depend on what ECU you are using

there are 2 very different and incompatible 993 Motronic setups

1) the 55pin OBD 1 Motronic 2.10.1 used on US MY'95 and also used on all RoW n/a 993s from MY'94 thru MY'98. These ECUs expect 1 oxygen sensor signal, in stock form the sensor is located in a mixing chamber where both sides dump exhaust. In modified systems the O sensor is usually located in one side or the other and that will provide sufficient control feedback for both sides.

2) the 88pin OBD 2 Motronic 5.2 used an all 993tt and all US MY '96 thru MY '98 993. These ECUs expect a minimum of 2 precat O sensors one on each side, the exhaust on these is different from the MY'95 exhaust in that there is no mixing chamber, the 2 sides are always kept separate and there is 1 precat O sensor per side. The car will run fine w/ just those 2 sensors but will throw codes and will fail any inspection where the codes are read as part of the inspection process. If you are using these in a t/p situation where you do not care about codes you can leave them off, in an oe situation you will need the 2 post cat O sensors as well as the 2 precat O sensors

[Deadeye]

Thanks Bill, this will be track only so no need for the second pair on sensors. I have the 88 pin '96 stock ECU, but searching for a '97/'98 unit. This ECU seems to be the red headed stepchild of ECU's.

[Bill Verburg]

Originally Posted by Deadeye

Thanks Bill, this will be track only so no need for the second pair on sensors. I have the 88 pin '96 stock ECU, but searching for a '97/'98 unit. This ECU seems to be the red headed stepchild of ECU's.

Yes, the '96 is by far the hardest to deal w/ the RoW and US '95 the easiest

The '97/98 in the middle

the ECU is expecting 2x pre cat O sensor readings

on the right are the pin assignments for the 88 pin Motronic ECU, pin 18 and 19 are the ones that are wanted, pin 76 and 77 can be left unused as long as you don't car about throwing codes

[Deadeye]

Awesome chart Bill, much easier to read than the wiring diagram in the service manual. Going to my favorites.