Car Lambda fail

[KemppiFrog]

OK, our shopping trolley, a little old Twingo, failed it's CT (MOT) on the lambda emissions (plus a few other fixable things)
This is the old pushrod engine one from '95. But the donk has only 125K km on it, not a lot for them. The exhaust system is a bit rough, but I pugged it up with Holts for the test and it doesn't leak.
So, what are the most likely probs with it? I will change the down pipeback to the rear end with a fresh can. But what else will effect the reading? Likely it needs a new air filter?
Any advice appreciated. Mrs KF loves the little thing. I got her a a Scenic, which languishes unused because it is too electronic. (Not fond of it myself..)
KF

 

[Wallace]

When was the oil last changed?

 

[m_c]

If you're confident there are no obvious faults, and the lambda reading isn't too far out, I'd start with a good old italian tune up before spending much time diagnosing.

 

[Pigeon_Droppings2]

Check the lambda sensor?...I would check the air filter and associated piping for air leaks.

 

[jsf55]

Air filter and plugs and good run out

 

[mr haynes]

When you say lambda emissions do you mean it passed the co and hc parts?

 

[chris y]

Any leaks in any part of the exhaust system could be the cause. It sounds like you have done a bit of bodging, I know you think its airtight, but are you sure?

As Mr Haynes said, tell us all of the emissions results.

 

[KemppiFrog]

Thanks for the input.
The car has not been used since the plague arrived, but I did give it a buzz to clear things. Oil, prob not for year, but well in milage.
CO was O.OO (range 0.5%) at idle, same at speed. Lambda was 1.048 (range 0.97 to 1.03) Due to it's age, that is all they test.
So, going to change the exhaust from the manifold back. Air filter, plugs and oil (& cross my fingers)
The tests last for two years here and you get two months to fix a fail, unless it is unroadworthy.

Pideon. How do you test the lambda sensor?

 

[Melvyn Best]

The Lambda reading is high but the CO is very low which would indicate a very weak mixture. Air leak either inlet or exhaust , CTS , air intake temperature sensor, MAP or MAFF sensor, faulty Lambda sensor can all cause the problem . It might be worth putting a bottle ,or even two, of injector cleaner in the tank and giving it the Italian tune up? A digital multimeter can be used to test a Lambda sensor , connect the positive lead to the Lambda signal wire using a back probe, neg to earth and scale to lowest DC voltage check with the engine running , from memory your looking for a reading of between 0.5 and 1.0 volt which should fluctuate

 

[KemppiFrog]

Thanks Melvyn, I have a decent Fluke meter so will give that a go, along with checking the rest for leaks. I did change the injection body after probs starting last year(single point) Since then it has run very well and starts on the button. Car has done 300K km or so, but this engine only 125k.