W124 Lamda Sensor

[hitt]

Hi,

I have a 1991 W124 Coupe 230CE. I have purchased and aftermarket exhaust (no CAT). Currently my downpipe has a lamda sensor attached. The new downpipe doesn't have a hole/thread where I can attach the sensor.

What would be the result of running the car without the sensor connected? I'm guessing the car would run a rich fuel mixture to be on the safeside?

I don't have the option of using the current downpipe as my exhaust is currently a straight thru system, completely welded together throughout.

My other option is to drill a hole in the new downpipe and have a bolt of the correct size welded onto it, so that I can screw on the lamda sensor.

Any help you can provide would be greatly appreciated.

 

[ms500]

I would say drill a hole myself; I think the Lambda is pretty important to the correct operation of the engine.

 

[Number_Cruncher]

>>What would be the result of running the car without the sensor connected?

If you mean without the sensor electrically connected, then, the system will revert to open loop operation, and probably would set a fault code.

As your car is a 1991, (i.e., pre 1993) it never needed a cat to meet MOT & emmision requirements, and I would imagine that here is a way of coding the ECU to tell it whether there is a cat & lambda sensor or not. This may be either via a multi-position electrical coding plug, or via an earthed coding wire from the ECU. If this is the case, you could re-code for open loop operation, and then run legitimately without the lambda sensor.

The remaining system sensors will be enough to allow your car to run like most other 1991 fuel injected cars - always in open loop mode. Until the ECU of post 1993 cars switched to closed loop mode, the lambda sensor does absolutely nothing - I suspect most don't even feel the switch over from open loop cold running to closed loop when the sensor heats up enough to begin working.

Someone who knows the system in more detail re coding plugs, etc, will be along shortly.

 

[hitt]

I like the idea of recoding the ECU by hardwiring it.
If anybody is able to give any info on how to do this it would be greatly appreciated.

Otherwise I'll go down the route of drilling the hole and finding someone that is able to weld the bolt on for me to enable me to attach the sensor.

Thanks again for the comments so far!

 

[grober]

Why do away with the Lambda sensor if the car injection system was set up to use one. You might well "get away" with not using one and using the car in open loop mode but you won't get the fine mixture control a feedback loop will provide. This will almost certainly give the car a poorer MPG and at the price of petrol nowadays----------??

 

[Number_Cruncher]

>>This will almost certainly give the car a poorer MPG

I'm not so sure Graeme - prior to the emissions laws which took effect in 1993, fuel management systems could allow weak part load running, and richer full power fuelling.

After the dead hand of political meddling made itself felt, to allow 3 way catalyst function, engines have been constrained to run at stoichometric, which under part load conditions is actually richer than a pre-lambda sensor engine would run, and hence wasteful of fuel. If anything, IMO, closed loop running actually reduces mpg.

If the car were mine, I would be looking at wiring diagrams for pre lambda sensor cars, and post lambda sensor cars to see if there's an obvious coding.

 

[Dieselman]

After the dead hand of political meddling made itself felt, to allow 3 way catalyst function, engines have been constrained to run at stoichometric, which under part load conditions is actually richer than a pre-lambda sensor engine would run, and hence wasteful of fuel. If anything, IMO, closed loop running actually reduces mpg.

Good point. The fuelling is set to deliberately waste some fuel down the exhaust to fuel the cat. Without excess fuel it can't fire.

 

[hitt]

Part of the reason I want to change the exhaust is that some years ago the original CAT on the car failed. This was my first car . . and I decided I was going to fit a custom made exhaust to the car. Nice straight through free flowing system. Wow the car sounded great, real grunt and seemed to run very well on the motorways, with the power seeming to peak between 3500 - 4000 RPM. Great when you need to overtake.
But now the great sound of the exhaust (constant droning) gets on my nerves and the overfueling (which you can smell at times) is too wasteful for my taste these days, with fuel costs rising.

So I've decided to fit the original (3rd party) design exhaust and find a way to reduce the overfueling.

This hardwiring of the system has certainly got my attention! I'll see if I can find some wiring diagrams of the pre-cat system. I do have the technical manual on CD, however being American, it doesn't cover the 230 (102) engine. So if there is anyone out there with a diagram for the 102 engine, pre/post CAT I would really appreciate a copy!

 

[grober]

It would appear that there was a reference resistor for the CIS system. I thought there was only one for the ignition system but you live and learn. The bad news is that on early cars ( both KAT and non KAT cars) it was external but on later ones it was hard wired into the ECU circuit board. Might be able to tell you more but would need the detailed engine number first since there are a huge number of permutations it would make your eyes water.

 

[hitt]

Hi Grober,

I've just sent you a PM with my engine number.

Keeping my fingers crossed now!

 

[hitt]

Thanks for the PM Graeme.

Unfortunately Graeme has PM'ed me to let me know that he hasn't been able to dig up anything concrete based on my engine number.

Does anyone else have a solution to avoid using the lambda sensor and potentially getting a better fuel economy out of the car?
Any way to revert back to the older system of cars without CATs?

Otherwise I guess I'll be getting a hole drilled and the sensor attached.

Many Thanks!

 

[kth286]

I would return the exhaust you have just purchased and ask for the version with Lambda hole in it - they must offer several designs for different generation cars, surely.

 

[hitt]

kth286. Thanks I considered doing just that. However, the pipe that does contain the hole also has the CAT on it. The cost of that pipe alone is more than I paid for the entire exhaust system and fittings.

So by the looks of it, I'll drill the hole and get a bolt welded on. Or go get myself a welder and learn how to do it myself I'm always up for the chance of learning something new!