1996 E36 post cat sensor / remove cats

[russellc2 9]

Hi all,

Wondering what others have done when removing cats (track car) with the post cat O2 sensors on an E36?

Can you run some kind of resistor to trick the DME to think they are still in place? My 328i has 2, but I'm about to install a new cat less exhaust. They are 2 wire sensors if that helps & I assume it's just a temp / cat efficiency sensor rather than full O2 sensor like the ones in exhaust manifolds.

Cheers,

Russell

[KwS 2425]

Depends on the car. My 95 M3 had the cats removed, and in doing that both O2 sensors were also removed (just unplugged and connectors tucked away). Yes, it threw a code, but it also didnt have a CEL so the only issue was when it was scanned. Didnt have any drivability issues, not sure if fuel economy suffered as it pre-dated my ownership and quite frankly i drove it like the car it was so consumption was pretty high anyway.

[russellc2 9]

Thanks Kelvin, that's what I've seen so far too. With them unplugged the cat / exhaust temp light comes on the dash but no CEL so far. I haven't driven yet but I'm not too worried about fuel consumption on hill climbs and track work too

Cheers,

Russell

[hybrid 1043]

Cats and pre cat O2 sensors are two different things as far as the DME is concerned.

Removing the O2 sensors will remove closed loop operation. It will cause the DME to default to a lookup table for fueling. No more power is gained by removing them. In some circumstances power will be lost as it will run more rich as a fail safe.

Removing cats are a different story. Removing cats will increase exhaust flow however it will remove back pressure. You will get a short term gain from cat removal in the top end however this can offset torque with the removal of back pressure.

The DME has cold start pre-cat warm up program and other emissions (SAP) and EGR programs which can be switched off by a competent tuner.

You can remove the DTC function from the DTC table. Again a proper tuner should be able to do this.

In my MSS50 I have removed pre-cat warm up, SAP program and EGR. I have also have also changed my flag to no catalytic converter and removed the related DTCs.

I do however have my o2 sensors installed so I can retain closed loop driving conditions. My cats have been removed as I run straight pipes to a back box I also removed and blanked off and removed my secondary air pump and connecting hoses. I have programmed my DME to handle it all and to remove cold start issues.

**Edited for correctness... few sleepless nights lately. Babys are fun.

[KwS 2425]

I should've also mentioned my cats were replaced with a pair of resonators in order to keep the back pressure up

[russellc2 9]

Thanks Josh, although I'm not touching the primary (or pre-cat) o2 sensors in the headers, which I understand are used in closed loop operation. That would be bad!

I'm replacing the cat's with resonators, so no-where to mount the post-cat sensors. Then I'm going with turbo style muffler at rear

Question Josh, do you still have the rear / post cat sensors on your system, or just primary sensors which I assume are also in the headers on your S50?

Cheers,

Russell

Edited February 3, 2016 by russellc2

[*Glenn* 854]

I think you'll find the after cat sensors are overheat sensors and not 02 after cat oxygen fuel trim sensors

Edited February 3, 2016 by *Glenn*

[hybrid 1043]

Yep your right, sorry I typed post not pre. I meant pre.

[russellc2 9]

Thanks Glenn / Josh, that's what I was thinking. So you guys have just unplugged and / or re-programed your DME to get rid of the cat overheat light?

I was thinking of just pulling the bulb if they never effect the tune....

[hybrid 1043]

I have edited my mss50 32kb binary and switched catalytic heating off in the calibration space.
Basically I have taken the good bits from the ZA calibration and kept the EU tune as for a road car you cant get much better than the EU map calibration. Race car you can get more power as the coolant conditions are a known entity. IE doesnt trigger knock.

Mine only has 2 pre cat o2 sensors. No post cat system for the mss50 3.18 software.

[*Glenn* 854]

Thanks Glenn / Josh, that's what I was thinking. So you guys have just unplugged and / or re-programed your DME to get rid of the cat overheat light?

I was thinking of just pulling the bulb if they never effect the tune....

I just cut mine, soldered them together, black heat shrink...job done.. no effects or codes