Emissions question

It would appear to be running over rich, over time that will ruin the cat. But if not too severe will seem to run quite well. My first thought would be check that the coolant is getting up to temperature (thermostat) and then coolant temp sensor which is incorrectly telling the ecu it is colder than it really is.

The problem isn't the cat, or at least not the basic problem. The basic problem is massive over fueling indicated by the high CO and low lambda values caused by either a failed lambda sensor or as Mr Cheerful suggests a failed temp sensor. This may well have then ruined the cat but equally that could still be fine and has been replaced needlessly.

A failed cat with everything else ok would at most just cause a very slightly elevated CO, say 0.5% but the MOT lambda value would be correct at close to 1.00. All the cat does is convert the very last dregs of CO and HC to CO2 and water. It can't remove any massive excess of pollutants which are always caused by a more basic fault.

The high HC readings also indicate that combustion isn't taking place fully either and lots of unburned fuel is getting through which could be bad plugs, worn valve seats or god knows what else. A compression test would help diagnose internal engine problems.

I'm pretty sure it's warming up okay and the thermostat is working properly. Is there a way to test the coolant sensor?

Thanks.

Tim

Thanks to all. Quite a bit of food for thought here and I guess my daughter has to consider how much she wants to spend on this old car.

I rather suspect that the cat has been replaced too hastily but that's done now and not a lot I can do about it. For a 1.3 the consumption has been a bit on the high side which would fit with an over fuelling problem.

Given that my daughter's money is tight (and my DIY capabilities with cars isn't that great), what would be the most cost effective way of narrowing down the problem? I don't have a compression tester and being realistic, hope never to have to use one but a change of plugs and maybe temperature sensor is probably within my scope.

I presume we would need to repeat the emissions tests to check if things were okay afterwards?

Thanks for all the suggestions so far.

Tim

Does the temperature gauge read correctly? A temp sender will be cheap. A generic lambda will be cheap. Neither will be particularly involved to fix.

Almost certainly, she'll recoup those savings on the next tank or two of fuel.

If you can find the resistance-temperature graph, then with a multimeter, check that it's giving the right readings when the engine's cold-warmish- hot.

But it's barely worth the effort. A new sender'll be cheap.

oddly enough just a week or two back a corsa came in with poor running and the MIL on, the code said CTS, so I removed it and checked its readings at various temperatures, all were spot on, so I checked the readings at the ECU, just the same, so it was a puzzler as to what was wrong, having now spent an hour or so testing I bought a new sender, instantly it ran fine and has not been any further trouble. Sometimes it is just better to whack a new bit on than mess about. Same thing happened with a MAF on a fiesta, but there was no code or MIL light, all readings were in the range they should be, but a replacement one from a scrappy made it run perfectly, out of interest I checked the replacement readings and they were very slightly different to the duff one, but still within standard tolerances.

Sorry to be a pain but a quick google suggests over a £100 for the Lambda sensor but that probably isn't a generic one. What's the best place to source things like that?

Tim

online searches, but toyota lambdas are unusually expensive 250 quid or more for some genuine ones, but most are available pattern, but unfortunately they still are a 100 quid or so. how they work/testing: