Author Topic: M42 O2 Sensor in 2 pipe exhaust (Read 3994 times)

Asterian · « **on:** August 03, 2012, 05:20:23 AM »

Hi all,
for some reasons I have 2 pipe exhaust system fitted to my M42 engine.

Oxygen sensor is installed like on following sketch, i.e. in part where both pipes inner area are connected, but for sure there is no present good mixture of exhaust gases.

To make decision for making x-pipe connection or leaving everything like it is
- would like to ask - is there real difference for M42 O2 Sensor to "read" exhaust from just 2 cylinders or from all 4 cyl, mix?

bmwconnect · « **Reply #1 on:** August 03, 2012, 11:56:05 AM »

4cylinders. If a injector begins to fail ( Dirt, slow open, or stuck open) on a cylinder that you are not monitoring the DME will won't be able to compensate and you will ping under part load and blow up. Also you won't get a CEL and most likely will never be prompted to investigate.

Asterian · « **Reply #2 on:** August 12, 2012, 01:38:05 PM »

If injectors of something else begins to fail - its abnormal working conditions..
But if we will take like default that everything is working well - will it be any difference in my installation and standart?

Asterian · « **Reply #3 on:** August 19, 2012, 02:05:29 PM »

Lets rephrase question. Does somebody here has 2-pipe exhaust like me and how o2-sensor was installed?

MLM · « **Reply #4 on:** August 19, 2012, 08:01:03 PM »

I dont have a twin pipe (yet) but thought i would post up some ideas on the subject.

Your setup as drawn looks fine from a gas sampling point of view (though maybe not best for flow) as i imagine the box would introduce a decent ammount of turbulance mixing the two gas paths. I wouldnt change it for the sake of it unless doing somthing more drastic like a full new system.

If i were to change it i would use a x pipe with a nice taper to smooth flow and place the sensor in the intersection. This would be essentially the same as all the pipes joining into 1 pipe.

Sampleling off just two cylinders only may be less ideal. I say this as I have a RHD E36 (different headers to you USA lot). On the factory headers 1 & 4 (joined) primaries are relativly long at 350mm ish. The other pair (2&3) are very short at 120mm. Therefore it would be reasonable to assume if chasing all out performance that different things may be happening in these cylinders compared to the other pair. (scavanging reversion etc) What may work for one pair of cylinders may not for the next and it may change through the rpm band. You would be effectivy be tuning a 2 cylinder engine and hoping the other 2 cylinders matched.

bmwman91 · « **Reply #5 on:** August 19, 2012, 09:28:23 PM »

Did the car some like that? That has to kill your low end torque! Was a custom chip burned for it? I would look for a stock M42 exhaust ASAP.

Anyway, the O2 sensor as it is installed in your diagram should work fine.

Asterian · « **Reply #6 on:** August 21, 2012, 02:15:27 PM »

In fact my setup: M42 engine from 89' E30 with stock front exhaust part:

Asterian · « **Reply #7 on:** September 09, 2012, 03:25:47 PM »

Finally I got x-pipe installed with lambda in the center. For a moment I feel no difference with previous setup. Just a good feeling that now exhaust looks almost like M3 one.