catalytic convertor - no sensor?

[johnsredarrow]

Hi guys, I come in search of knowledge again...........

My neighbour has a 240 Torslanda (H reg 1989) with a B220F engine.

Having heard the exhaust blowing yesterday, we had a look and the catalytic convertor has rotted and has a hole in the back.

The feeling of initial panic (due to the prospect of replacement cost!!) was quelled after reading the forum and finding out that it is OK to permanently remove the cat with no detremental effect. Fantastic!!!!

But as I understand it from the Haynes manual, there should be a sensor on the exhaust pipe after the exhaust changes from two pipes into one and before the cat........ except all there is is a very-none-standard looking hexagonal bolt (probably M8) screwed into the exhaust pipe approx 6 inches infront of the cat and I'm guessing that this is where the sensor should be ..... but isn't.......
And there are now wires anywhere nearby which look like they should be fitted to a sensor........

The car runs absolutely fine so do we just chop the cat off and remake the pipe or is this sensor something to be concerned about??
There are no warning lights showing on the dash........ and it flew through the emissions test at the last MOT........

Any ideas guys?

Many thanks for any advice

John

[classicswede]

The lambda sensor wires connect to a two pin plug on the front bulkhead with a seperate single spade connector for the lambda signal wire.

To remove the cat set bet is to buy a front down pipe for a non cat car.

[johnsredarrow]

OK, thanks for that!!!

And can I just correct me original post. Its a B200F engine not a B220F..........

I still confused though. How does the engine still run without this sensor when it seems to be an original part of the setup?

I mean if the crank position sensor wasn't fitted then the engine probably wouldn't run so how does the engine run without the lambda sensor?

Or am I barking up the wrong proverbial tree!!??

Is this 'hole' with the bolt in the place where the sensor should be???

If anyone can enlighten me further, I'd appreciate it!!!!!!

Thanks!!

John

[Clifford Pope]

I agree there surely has to be a sensor somewhere. The standard advice when about to eliminate a cat from a system that does not legally require one is that the sensor has to be left or put back into the exhaust pipe in order to provide the proper signal. I didn't think the engine would run properly if the sensor was just tucked up somewhere in the open air, or unplugged at the bulkhead.

Three different positions have been used for the sensors;
1) in the cat itself
2) in the pipe a few inches forward of the cat
3) in the exhaust manifold

Unused bosses, if present, obviously have to be plugged.

I would look for the terminal connectors on the bulkhead inside the engine compartment, just in front of the driver, and see a) if anything is plugged in and b) where it goes.

[dgbalfour]

My J reg B200F had the sensor mounted on the front of the cat housing, try looking more closely at the cat itself.

I removed the cat some years ago. I had a small boss made up for the sensor and had it welded onto the new pipe. It's been fine ever since.

The engine will run ok if you remove and disconnect the sensor. The ECU uses a default mapping if it can't get lambda information. It doesn't run badly actually, but it is better with the sensor installed.

David

[Clan]

Are you sure its not a B200GT ? they have everything but the cat and lambda probe as far as i remember...

[johnsredarrow]

Gentleman thank you for your replies!!!!

Errrrr...... and now its time for me to look a bit daft.........

The catalytic convertor does indeed have a flamin big sensor on the rear of it......

I looked under the car from the drivers side.......... and the sensor is only visible when viewed from the passenger side.....!! So when I saw the boss on the exhaust pipe with the bolt screwed in, I said 'Theres nothing in there' and my neighbour (who is really deaf) misunderstood what I meant and thought that I was saying that there should have been another 'something' in that hole. He didn't say that he'd already seen the sensor on the other side of the catalytic convertor!!!!
He cannnot understand electrics and sensors are just a complete foreign language (he is 79!). You want to see him with a wiring diagram..............
However this is the same man who made a new sill for a previous 240 with a piece of sheet metal, a hammer and a kerbstone (and nothing else) and when he had finished, it fitted perfectly. I'm not joking, it was fantastic to watch..........

But anyway he is going to buy a new non catalytic converter exhaust pipe and we'll weld a boss on and fit the sensor into that. And just for the purpose of proving a point, we disconnected the plugs to the sensor and the engine started and ran the same as normal. This was however just with the car standing still. Whether it would be any different going along on a run I don't know.

Just out of curiosity, if the sensor is just going to be 'reading' exhaust gas which hasn't been through a catalytic convertor instead of exhaust gas which has been through a cat, how will it affect the mapping of the ECU. Will it change any engine settings?

Thanks again for your help!!!!

John

[Clan]

The sensor should monitor the gas BEFORE the catalytic converter , so having a cat or not wont make any difference to the lambda operation .

[Suterman]

The system will run ok with the sensor unplugged but better with it plugged in.

It uses the sensor to read the amount of oxygen in the exhaust and determines the richness or leanness of the exhaust from that, in turn the system decides if the engine needs more or less fuel at the moment after the reading.

It already knows a ballpark figure for the given revs on how much fuel to inject, the sensor helps the system run more precisely and use less fuel than say a carb would.

[johnsredarrow]

The new exhaust pipe will be on order very soon.....

Thanks everyone for your help!!!!

John