(Re)Fitting a lambda sensor to an M42

Sun Apr 07, 2013 7:57 am

I went for the MOT yesterday, and while it passed on emissions (1990 car so less stringent) the lambda reading was around 1.2 at idle!

I think my car was fitted with cats and a lambda from the factory, but the previous bodger / owner removed them to fit a SS exhaust, removing the lambda boss at the same time. The airbox has been modified to take a different AFM (Well I assume it has, unless BMW used a 2" philips head screw from B&Q to attach it to the airbox!)

So my question is this: what do I need (parts wise) to refit the lambda and go back to closed loop control? I assume all the wiring loom is still present, but do I need a different ECU? I'm breaking an M42 E36 Compact at the moment, can that donate it's AFM or any other parts?

Sun Apr 07, 2013 8:47 am

to refit the lambda/oxygen sensor will require a new sensor with correct plug to connect to the connector clipped under the battery tray.
worth getting the clips to route the cable correctly away from the exhaust down pipes.

also need to remove the shroud that runs across the back of the engine bay and find the loom connector with grey/black wires.
if the lambda is present, the grey/black connector will need to be disconnected to allow the ECU to work in closed loop mode.
The ECU will need about 30 minutes of working to learn the new signals generated by the lambda sensor.

Sun Apr 07, 2013 8:18 pm

Cheers Mark, so the AFM and ECU shouldn't need changing? Sounds a fair bit easier than expected!

Mon Apr 08, 2013 4:44 pm

mark_i wrote:
also need to remove the shroud that runs across the back of the engine bay and find the loom connector with grey/black wires.
if the lambda is present, the grey/black connector will need to be disconnected to allow the ECU to work in closed loop mode.
The ECU will need about 30 minutes of working to learn the new signals generated by the lambda sensor.

Is this currently connected or disconnected, bet the bodger didn't change this connection when they removed the lambda. May cure your ills without refitting.

Mon Apr 08, 2013 7:51 pm

Jos wrote:Is this currently connected or disconnected, bet the bodger didn't change this connection when they removed the lambda. May cure your ills without refitting.

If I read that correctly my car with no lambda needs the connector connected? If so then the bodger isn't as bad as he first seemed.... except for the attempt to fit an alarm / immobiliser under there too....

To be honest the engine runs fine as it is, I just A) think 1.2 is too high at idle, B) want a lambda for when I build a megasquirt into the stock ECU box and C) like meddling

Mon Apr 08, 2013 10:18 pm

AFMs can differ. The afm on cat car does not usually have the CO adjustment pot- there is red bung where it should be.

Where a lambda sensor is fitted, the wire across the bulkhead is left disconnected. If the lambda is removed and an afm with the CO adjustment pot is used, the wire is connected.

Are you sure your iS had the lambda and cat fitted when new?