Lambda sensor conundrum!!! E36 BMW

[vaughant]

After some ideas from the educated in this field, or really anyone with half a clue!!
Have an e36 cab which originally had a 2.8 m52 fitted. Lots of cooling issues, a bodged ripped off head repair later and I give up and shove a known good 325i m50 motor in it.
Starts runs and drives fine, but have emissions issues.
This is due to a number of factors namely different lambada on 328's (Titania instead of zirconia or vice versa) and the fact there's two of them and the fact I thought it was good to solder in the loom which apparently doesn't work due to the lambda using the air gap in the cable to get the O2 reference.
No idea if that's really true.
Anyway.
I need to fit in the 325 lambda (single, much more basic affair) into the downpipe. Problem is in the now binned 325 downpipes I'm certain there was a 2 into 1 pipe and the lambda sat in there, the 328 has two separate pipes the length of the system and no obvious join point as the cats even look separate.
Option 1:I can mount the new lambda on either one of the old 328 pre threaded holes but will this then cause it to mess up the ecu as the readings are only from one bank of cylinders as the manifold is 2 piece?
Or
Option 2: Could I fit two lambdas into the two pipes and crimp the appropriate wires together to split the signal as such and get a balanced reading across both manifolds hence the ecu should then read the average of the two??
Or am I worrying about nothing and the one sensor fitted to one downpipes will do a perfectly adequate job?
The car is not going to be used in anger or do huge mileages but of course it needs to pass an mot etc and not do 12mpg!!!
Thanks in advance.

[ejenner]

It is tempting when you've done so much work to assume the worst.

One major difficulty I can see you're going to have is with finding out if you've actually resolved the issue as there are very few of us with an emissions testing kit available to hand. So what will you do, go to the MOT testing station and ask them to test it each time?

It is possible from the emissions print-out you got from the MOT station to see how the car has failed the emissions test. If it fails in one way then it's CAT related, if it fails the other way then it's a fuel-injection problem. CATs do fail so that's not impossible either.

A common fault with the E36 is the air mass meter failing. Actually many BMWs of that era have that issue. It makes the engine run rich.

If you are going to start fiddling with the lambda probe then out of the two options you've proposed I'd definitely go with option 1. Option 2 will dramatically change the reading. Option 1 will give an accurate reading but only for the cylinders it reads for. If you have an engine problem on any of the other 3 cylinders it wouldn't change the reading.

The other thing which can cause emissions issues are the oil breathers and cam cover gasket. If these are in poor state of repair engine oil can enter the intake and run through the engine. It's unlikely to be that problem though as it would take a lot of oil going through the engine to knock the emissions out of spec. Can also check for a blocked air intake.

[vaughant]

Thanks ejenner, that makes sense.
Probably didn't clarify previously but both cars were running spot on before the swap emissions wise, both had newish mot's and I never had any issues with the cab before hand.
I can see what you mean with regards to the lambda sensor only really showing an issue with one side of the engine, makes total sense and actually makes my life a lot easier as there are already welded in bosses from the factory to put the lambda in.
The mot tester said he was confident that there was no lambda reading hence emissions all over the place.
I can but try it, worst case scenario is to get a 325 downpipe and fit it in the original location but apparently the 328 manifolds and system were a good upgrade for the 325 hence why I used them.
In fact looking at images and jogging my old memory the only difference is that the 325 system had a welded interconnect pipe between the two downpipes under the car where the lambda sat inbetween which frankly is not much of an improvement over putting it in one pipe only.