Retrofit Catalytic Converter

[Alpinweiss]

Hello All,

New to the forum, apologies if this topic has been recently discussed - unfortunately the search found nothing with my subject keywords...

I am looking good tips and tricks to retrofit a catalytic converter to factory non-cat 318is (E30). The original part from BMW is NLA, no help from there. I have understood the E36 could be used by modifying it? From exhaust manifold to catalytic converter pipes need to be adjusted to get the correct angle for E30? Another option is to build one using universal cat. Any recommendations?

Second related question is the Oxygen Sensor. To my understanding, the E30 wiring harness has the plug for the sensor in the engine compartment, more specifically underneath the battery holder? Should this be just a plug and play - I was told E34 518i part would work just fine (only the wire would be bit too long).

Any comments and/or proposals are welcomed.

Best regards,
-Sam

[DesktopDave]

I haven't done this myself, but I'd assume an aftermarket high-flow unit would be your cheapest bet. Likely it'd work better too, given that you can specify the entire system. I'm pretty sure that Walker and other exhaust manufacturers produce these parts, at least in the U.S. OEM style is expensive, about $350 or so for the front half (downpipe, cat, resonator) last time I checked.

I can tell you that the oxy sensor four-pin does mount on the bottom of the battery tray. It is a universal Bosch part produced in many different lengths. I'm pretty sure I'm using an E34 pre-cat sensor myself. Be sure to disconnect the CO pot adjuster at the firewall before enabling the O2 sensor. It's a single-wire connection near the relay block IIRC. You may also need the sensor heater circuit relay, perhaps an NA market DME, & etc.

You could probably get away without an O2 sensor if you're running a cat; alternatively you could also install a wide-band sensor with an emulated narrow-band signal if your DME supports it.

[bmwman91]

I have been using Magnaflow weld-in cat's for years now, and it allows me to pass emissions testing in one of the strictest places in the USA. They are ~$150US, and shop labor is usually around $80US.

As Dave mentioned, you will need to disconnect the CO adjustment wire up on the wire loom on the fire wall, and you will probably need to install an O2 sensor heater relay (goes on the firewall next to the main relay and fuel pump relay). I do not know if you need a new DME unit, but I am pretty sure that you will at least need the EPROM chip from a car that used a cat. It would probably be about the same cost to pick up a used DME from someone versus just the chip, and you could be sure that it would work.

As far as which sensor to use, I have only ever used the OEM one. They are expensive though, and I am pretty sure that any Bosch 4-wire sensor would be OK. You might want to buy the OEM one the first time around to get the connector though.

[keflaman]

As Dave mentioned, you will need to disconnect the CO adjustment wire up on the wire loom on the fire wall, and you will probably need to install an O2 sensor heater relay (goes on the firewall next to the main relay and fuel pump relay). I do not know if you need a new DME unit, but I am pretty sure that you will at least need the EPROM chip from a car that used a cat. It would probably be about the same cost to pick up a used DME from someone versus just the chip, and you could be sure that it would work.

I'm fairly certain that all he'll have to do is install the 02 sensor, catalytic convertor, and disconnect the plug at the firewall. Per the E-30 Series Repair Manual, "...when the plug is disconnected, CO is regulated via the oxygen sensor."

Alpinweiss: can you verify for us what market your car was built for? By the way, why do you want to install a catalytic convertor?

[bmwman91]

Interesting. Maybe the ECU will detect the O2 input and switch to the right set of maps and control algorithms?

[keflaman]

Interesting. Maybe the ECU will detect the O2 input and switch to the right set of maps and control algorithms?

I think so. I had an '89 318is w/o cat and O2 sensor when I lived in Italy and I connected my Snap-On analyzer to read the DME with the plug connected and disconnected. That was five years ago, so the memory is a little foggy, but here's a few things I found searching -

See my last three posts on page 1: http://www.m42club.com/forum/index.php?topic=8572.0

Here's a snippet from the "Did we ever figure out the "Hot Start Problem'" thread: http://www.m42club.com/forum/index.php?topic=7757.35;wap2