240 General: Running with Lambda light on.

[146ken]

I am looking at rescuing the 240gl estate that is up for £200 on the sales forum. I do have a worry though that the owner says it has been running for many years with the Lambda light on. I am no mechanic and don't want to be faced with major engine issues.
What possible problems can be caused by running without addressing this issue?

[Glen Morangie]

I hope you do get it - I looked at it myself, but I just haven't got room.

I think (but may be wrong, as the lambda business is relatively new to me) it sounds as if the engine is running rich, which will take out the AMM and the cat.

So you will probably need an AMM and a lambda sensor, but otherwise there shouldn't be too much to worry about. You don't have to have a catalyser for the MOT necessarily, as it's a 1991 car. If you dispense with the cat you will have to either substitute a section of exhaust (these are available) or clear it out. It may be the cat has nothing in it, as otherwise it might have become blocked by now.

As soon as it's running properly any carbon build up will clear on your first motorway trip, overfuelling is less likely to be damaging to the engine than lean running in the long term, other than the items mentioned.

You'll probably have to do all the normal things, like cambelt, plugs, hoses, filters etc, as it sounds like it's had a 'zero maintenance' regime - just shows how much neglect a 240 will stand.

Strangely there is another just like it on ebay at the moment, also missing a door trim and with a broken bonnet hinge.

[Velorum]

Sometimes even when the running problem that caused the light to come on is rectified the light remains on and needs to be reset. When Ive done this is in the past I check that Ive got the radio code and then disconnect the battery for a few minutes. Worth a go.....................

[Glen Morangie]

Originally Posted by Ian Hutchinson

Sometimes even when the running problem that caused the light to come on is rectified the light remains on and needs to be reset. When Ive done this is in the past I check that Ive got the radio code and then disconnect the battery for a few minutes. Worth a go.....................

If the car's running I wouldn't recommend trying a reset until you get home. The ECU stores faults and makes adjustments, it's possible other adjustments have been made to counteract this (the idle is 1500 RPM) - it might work, but if it doesn't you're stuck until the ECU re-learns the faults.

Just my opinion of course, not everyone will agree.

[Suterman]

The lambda light comes on to notify you as a buyer that you are getting a bargain.


Its a good point about the cat, if the engine has been running rich for a long time it may have damaged the cat. It would be pointless trying to diagnose the problem until you are sure the cat is ok as a blocked cat damages the o2 sensor or at least causes it to give a dodgy reading leading to a bad air fuel mixture.

I would say the AMM will be ok as the car will barely run if it's faulty.


Once you have established the cat is OK, clean up (replace would be best, to be certain) the 02 sensor reset the ecus and try it again/read the codes with the OBD and see what it says, it might come up with a few things. If there is still a problem with the mixture (EFI) then the lambda light will come back on.


Raid the scrapyard for the parts needed.

[Glen Morangie]

If you do want it you may need to be quick now - as anyone reading this thread who might have been put off will be thinking - hmmm, a hundred quid's worth of parts and it could be back on the road!

[Suterman]

It's worth bearing in mind that prolonged running rich may cause premature wear on the engine as the excess fuel can wash the oil off the cylinder wall (bore wash) but only in very rich conditions (I Think)

Glen, if you are interested I will tell you what I know about lh2.4

All this is from memory so read up to be certain!

The computers in the car control the amount of fuel injected and at what time and when the sparks fire.

They rely on different sensors to tell them whats going on, like the Air mass meter, the crank position sensor and oxygen meter.

The computers are programmed with a chart or "base map" to tell the ballpark figures for how much fuel (F) they need to inject relative to the amount of air going into the engine (A), revs and throttle position to achieve the best air/fuel ratio (AFR) the ideal AFR for a petrol engine is 14.7(A) to 1(F) or 14.7:1 Don't forget that these cars have to work all over the worlds at extremes of altitude and temperature (air density) and the maps have to accommodate this, the boffins at Volvo don't want the car to break down at all if possible so they make the "base maps" run a richer rather than a leaner mixture (because it's safer) just to be on the safe side.

The o2 sensor tells the ECU how much o2 is in the exhaust mixture, this information expressed as a voltage to the ECU, more oxygen means the mixture is lean so the ECU will add more fuel and less oxygen means the mixture is too rich and so the ECU will lean out the mixture and fine tuning the "base map" to suit exactly the requirements of the engine at any time.

When everything is working fine the system is is closed loop mode (normal), meaning that it's reading the maps and adjusting the mixture according to the reading from the o2 sensor and other sensors hundreds of times a second.

When the Lambda light is on it means the car is using open loop or "base map" fueling settings, so in other words there is a fault that has caused the ECU to switch to open loop mode (mostly known as limp home mode)

So lambda light faults are fueling related.

Hope this helps, its only the basics, sorry if I'm rambling.

This is why I suggest that the cat may be bad,

[Suterman]

It is also worth noting that Lh2.4 is able to accommodate many more conditions in terms of air density (altitude and temperature) that it is ever likely to see in the UK and so is able to cope with much more fueling than it is set to at the factory, this means that it is possible to stuff more air into it (boost pressure) than the factory settings, the ECU simply reads that there is more air coming in (read from the o2 sensor) than the map says there should be and injects more fuel to compensate. That is what makes the Lh2.4 cars so tunable. NB. you do get to a point where the fuel injectors cant flow any more fuel and then the mixture will go lean. (pinging, detonation, boom, oil spill)

[Glen Morangie]

Thanks - a good consise summary of what's going on. Although I said "the lambda business is new to me" - it's really that I've only recently got a car that has the LH2.4 - in fact until a coulpe of years ago I'd more or less avoided fuel injection altogether.

I'm Ok with the fundamentals (as it's like a computer adjusting settings which would otherwise have to be 'median') - it's the 'when this fails it causes .....' I'm not so familiar with - but I do have the greenbook with the fault charts, and I'll need to remember it now.

[146ken]

Thanks for advice.
If my understanding is correct the best case scenario is a new O2 sensor would cure the problems and the ECU would reset itself.
Worst case would require new CAT, AMM etc,etc.

I have seen some photos of the interior and its well worn and grubby. Rear compartment has carpet worn right through. This car is never going to be beautiful again but it could serve as the dog carrier and take some of the wear and tear presently being visited on my GLT.