exhaust & O2 sensor question
 

Hi all, i've been a long time lurker and finally decided to sign up. I purchased a 96 ti locally with the intent of doing an S52 swap. After evaluating everything that needed to be done, I decided to purchase an already completed swap from a gentleman in FL.

The issue that I have is that FL. doesn't require emissions, but where I live in NM does. Right now, the car is setup header --> resonator --> muffler. I must have a cat and no check engine lights to pass here in NM. My plan was to have a local shop install a generic cat and a bung for an O2 sensor. However, I've noticed that the M3 exhaust has 2 O2 sensors.

I'm assuming that the 98 ti wiring was used and that there will only be a single connection for an O2 sensor. I'm curious to know how this problem was solved by others needing emissions. I'm also hoping that my milage will go up a bit once this is corrected.

Any thoughts or experience are appreciated. Thanks,
Jeff H.

Check carefully there may be a 02 sensor eliminator on the post cat sensor wire. (Very common when someone does a cat delete to keep the ECU happy.

Good point PDX. I need to trace out the wiring carefully and understand what is there and what is not. I understand very little about the swap. I understand that some portion of the M3 harness has to be in there. I'm hopeful that all the wiring for all 4 sensors is there. The check engine light is on after the previous mechanic cleared it. I have yet to read the codes.

So, if there is no eliminator in the circuit, is there a way to just go with one sensor instead of two? Maybe I need to look into an eliminator as an option.

Its very very common to do a OBD1 conversion on S52's because of tuning. Especially where emission testng is lax or non existent. In my state you'd have to have the cat and pre/post sensors in place or its a full stop you don't pass,,, If 98 had pre and post cat sensors, You probably need a OBDII wiring harness and put the sensors back.. If your testers look for them..

I'll need to dig in this weekend. Any easy indicators that i've got an OBDI vs OBDII harness?

So i did some digging today without actually getting under the car. I'm not sure what to look for to determine OBDII vs OBDI harness, but I did pull codes for the car. The OBD plug was under the dash, next to the hood latch lever. I've done a bit of searching and I think that if my car was setup as OBDI, I wouldn't have that port.

Here are the codes that I pulled:
P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control
P0173 Fuel Trim (think this is bank 2)
P1186 O2 Sensor Heater Control Circuit (Bank 1 Sensor 2)
P1188 Fuel Control (Bank 1 Sensor 1)
P1189 Fuel Control (Bank 2 Sensor 1)

This is definitely pointing to faulty or missing O2 sensors. I'm guessing that I'm in for 4 new sensors.

I'm still curious to know if I need to run 2, or if I can get away with running a single after-cat O2 sensor

I also have concerns over the I/M readings from the tools. The following were in a Not Ready status:

Cat - expected since it's nonexistent Evap - not sure what this is about
2Air - i think this may have been removed from the car
O2S - somewhat expected
HO2S - somewhat expected

Looks like I have quite a bit of investment and work ahead to get this car to pass emissions. Any experience in this area is appreciated.

I'd watch here and Craigs list for a part-out of a S52 car, the cats are integrated with the headers (At least they are on my M54) , you might be able to pick up a full kit off someone fairly cheap. Check BMW race shops they may have a takeoff header.

Engine swaps are almost never just a plug and play even if youve done several they always find new stuff to dazzzle you with.. :)

Not too many of those where i live :). I found an excellent custom muffler shop near me. The plan is to install a high-flow basic cat and put the headers 2 into 1 before the cat. I guess I'll have him install 2 ports for O2 sensors. My only challenge will be to find the wiring for the post-cat sensors (and coming up with the cash for 4 new sensors).

I'm not an expert. 96 and later cars require 2 sensors. 1 before the cat, 1 after. The 1st sends a signal to the ECU to make adjustments in the mixture. The 2nd looks at the exhaust after the cat and decides if the Cat is doing its job. If not it turns the light on. I think it is possible for the 1st to turn the light on also. I have seen folks run post cat simulators, I don't know how well they work out. Generally speaking BMWs and a few other cars don't like generic cats, many that work on these cars will not install non-OEM converters. I've simplified something the people send their life trying to understand.

Warren

Thanks Warren. The S52B32US motor requires 4 sensors: 2 precat and 2 postcat. This is due to the truly independent dual exhaust on the M3. I'm going 2 into 1 before the cat, hence my question on being able to get away with a single sensor after the cat. BMWs may not like generic cats, but i feel confident that a generic cat is going to be miles ahead of running no cat at all which is how the car is currently setup. If the generic can't get the job done, I'll consider getting an OEM M3 setup and cutting the cats out to fit my car.

Got the exhaust work done today and the car sounds great! I went ahead an had 2 O2 sensor ports installed post cat - I can always leave one capped if I don't need it. Now on to replacing O2 sensors. It seems like there's lots of discussion on NGK branded vs. Siemens branded vs. Bosch vs. BMW. Lots of price difference too - NGK is $75 vs. BMW which is ~ $250.

I'm sorry I forgot that they use dual cats and 2 pre and post cat sensors. I have way too many M42 and M44 cars. I wasn't focused on that detail.
I think you now have 1 pre cat port and 2 post. The ECU is looking for 2 signals pre cat so it can make adjustments to bank 1 and bank 2. I think you will need both post cat ports because the ECU needs to verify the the cat is doing its job for bank 1 and 2.
By now you can try it out and see what works or doesn't. It is unclear to me how it will react to a single cat with the sensors in the same exhaust stream.
Good Luck
Warren

I have two pre-cat sensor ports and two post-cat sensor ports; just as the stock configuration. The difference is that the two post-cat sensors are on a single pipe now. If there are issues with one of the banks, I can see some confusion by the overall system since the post-cat exhaust will be a mix of good and bad pre-cat exhaust. However, if the car is running well, I suspect that there will be no issues.

Now, I just need to find the connectors for the post-cat sensors. I'm hopeful that this is part of the M3 wiring harness that is required for the motor. Otherwise, it's going to be quite a fun job to determine where those wires need to connect to in the harness.