940 lambda and catalyst replacement

[Dirty Rooster]

Originally Posted by Ian Fozzard

The emission warning light came on on my 1991 945 with the 2 litre non-turbo engine. I was a couple of hundred miles from home so I drove back with a slightly lumpy running engine.
The exhaust and plugs are very sooty black so I am certain the engine was running very rich after the warning light came on (running perfectly beforehand).

So my question is: Will all of that carbon in the combustion space and exhaust give me any problems if I just replace the lambda sonde and the catalyst? (I am assuming that the cat will be damaged by all that sooty carbon so intend to replace it).

My concern is that the sooty carbon in the combustion space and the exhaust upstream of the cat will simply ruin any new lambda sonde and cat that I fit. Do I need to do any cleaning up (if that's possible?) to remove the carbon?

In my opinion the CAT would be damaged by unburned fuel mix or oil rather than soot, but the soot could've come from those nasties when they hit the CAT

You've got to find out what's wrecked your mixture,
cheapest check is to remove your airbox filter (temporarily. for testing) to see if air restriction was enriching your mix, which happened to me one time.

Another time my O2 sensor stopped working, lumpy drive, down on power in a rainstorm on the way to a day's work, which wasn't nice.
After unplugging and re-routing the O2's wire it started working fine again and everything went back to normal. Wierd stuff.

Edit: oh when your engine's cooled down reach under the downpipe and just wiggle your O2 to see if the hex nut has come a bit loose ...

Mine's the 1991 2.0 but with a turbo. So very similar.

[Ian Fife]

Thanks for this DR. After running a number of tests today and doing some checking of various bits obn the car, I've decided that the quickest test next is to just replace the lambda sonde and see how that goes. It is the original (27 years old!) so doesn't exactly owe me anything......

My 940 has the OBD1 box under the bonnet, and all the readouts so far keep indicating a lack of control over mixture - so the lambda sonde is the obvious place to start I think.

Disconnecting the lambda sonde made no difference to the running, so this is a bit more evidence that it's not doing it's job!

Ian F.

[bob12]

Just a comment from my personal experience over 29 years with same 745 with LH 2.4, and still the original cat (they don't build them like that these days!) it needs a hell of a lot of contaminant to 'kill' an old Volvo cat.

My cat has had it fill of bad mixture flowing over the plates on many an occasion when I have had engine management problems and had not learnt how to control it! It is still producing CO and HC levels within the later MOT requirements which are not applicable to the car.

[bob12]

Originally Posted by Ian Fozzard

Thanks for this DR. After running a number of tests today and doing some checking of various bits obn the car, I've decided that the quickest test next is to just replace the lambda sonde and see how that goes. It is the original (27 years old!) so doesn't exactly owe me anything......

My 940 has the OBD1 box under the bonnet, and all the readouts so far keep indicating a lack of control over mixture - so the lambda sonde is the obvious place to start I think.

Disconnecting the lambda sonde made no difference to the running, so this is a bit more evidence that it's not doing it's job!

Ian F.

Basically an 'on' lambda light just tells you that there is an engine management problem not usually a faulty lambda sensor. In the past I have changed the sensor for another OEM Bosch (not cheap!!) one, and it made absolutely bugger all difference.

Rather than change the sensor (maybe not easy) I would explore the alternatives first. Also disconnect the battery neg terminal to reset the ecu and clear the codes first to see if they come back. I believe that withdrawing fuse 1 (?) also does that.

[Dirty Rooster]

Originally Posted by Ian Fozzard

... replace the lambda sonde and see how that goes. It is the original (27 years old!) so doesn't exactly owe me anything....

That beats mine : seemed to be about 22 when it popped its clogs.

[aardvarkash10]

Originally Posted by bob12

Basically an 'on' lambda light just tells you that there is an engine management problem not usually a faulty lambda sensor. ...

Rather than change the sensor (maybe not easy) I would explore the alternatives first.

^This.

Honestly, if you do not understand how the system works AND you lack the desire ot learn, find a workshop that does know and hand it over to them.

The "lambda" light is to all extents and purposes a "Check engine" light. It does not necessarily mean the O2 sensor is faulty.

If you want to give it a crack, reset the ecu as Bob suggests, and run the vehicle until the warning light comes up again, then read the diagnostic codes. These will give you a steer in the right direction, but still need interpretation alongside any other signs and symptoms.

The lambda sensor is a bitch of a thing to extract - you will need a special tool (a claw foot deep socket ideally) and it may need a LOT of force to shift it. There is not a lot of space to swing a tool in so you end up with about 30cm of extensions and a good new vocabulary.

[Ian Fife]

All readouts from the OBD1 unit point to the lambda sonde failing, as do all the symptoms experienced.
Sonde came out easily with a 22mm ring spanner (it has been out previously when I changed the catalyst many years ago).
Awaiting new sonde(£50) from Germany.

What makes you think I don't understand the system??

IanF

[aardvarkash10]

the fact that you immediately want to replace two components that may yet prove not to be the problem without carrying out any other real diagnosis.

Nice that it came out easily - I hope the new one does the trick.

[Ian Fife]

Well this is the usual problem with many forums. You ask a question and no-one answers it, but respondents go off at a tangent and make many assumptions.
Please read my original request.
I was asking about carbon in the engine and the exhaust - nothing else!

Ian F

[ovlov236]

Hello Ian Just A Few Words On Your Volvo The B200f Is Prone To Overfueling This May Be Problematic At Mot Time With High Emissions Etc Etc high fuel consumption is Typical
However Please Check The Following The Coolant Temp Sensor not been fiddled with its A dual purpose sensor earths through the body remove the sensor the resistance should be 3.500 ohms cold measure between block and each of the pins and should be 300ohms hot if not replace sensor
Another Problem Is The AMM A Divation of as little as 0,25v can cause a upset in fueling also the signaling value is critical as well it must be clean you can check it with a oscilloscope if you find its not right and checked the earths replace the fine wire on the amm has a voltage of 5v to clean any dirt off failure of this can lead to your problems
Check Also Your ignition components exhaust for leaks AS others Have Mentioned sorry guys and girls if ive repeated things just my opinion on this engine Thanks Lou