1990 C4, manual ( in Spain), suddenly registers Lambda emmissions too High
 

This car has 68000 true miles on the clock, and has never failed Lambda emission tests, last year it passed with a 1.004 reading, this year it has failed with a 1.241reading.
It does not register any error codes on any module, and has a brand new 02 sensor.
The car runs just fine and does not sound any different to last year, and cant find anything obviously wrong.
I am totally bemused. has anyone had a similar experience.
Many thanks

MT

You results don't translate to U.S. emission terms. Hydrocarbon ( HC) Carbon Monoxide (CO) and Oxides of Nitrogen (NOx). Do results show which was out?
Small vacuum leak could cause MAP sensor to add fuel causing rich condition. AIR system can cause O2 sensor to read wrong. EGR high NOx. Degradation of cat converter after all 29 year old car.

I assume you failed with too high unburned HC reading, the Lambda of 1.24 means lean to me but I assume you actually mean the car is rich. Make sure there are no fuel leaks at the back, I am assuming it failed a tailpipe test and any fuel vapors from the fuel tank will cuase a failure of a test for high HC (unburned fuel)

Thanks for your reply, the lambda data is the coefficient measurement of all the components in the air at the tip of the exhaust, and logically would imply a rich mixture, although I am out of my depth on this. The problem is that there is no precedent and no error codes the car has never failed anything so I am out on a limb, and there in no manual adjustment as far as I know and replacing sensors without checking the gas in the exhaust seems and you would have to go to the test station each time, I already done it 3 times, all failures.
most service stations here do not have Lambda measuring equipment as they are deemed too expensive. I am now trying to use an old Acer laptop running windows 2000 with a ODB Diagnostics GM ALDL ODB1 USB cableI have, I downloaded the programs, EFI Live, Moats ECM852, TTS Datamaster, TunerCat, Tuner Pro &RT and as I have never used any I cant tell which is the best to use in this case

You really need to just be able to monitor data. Do you have factory mauals? Section 6E is for emissions. There is a table with what normal data readings are.

INTegrator or short term fuel trim 128 range 120-140
Block LearN or long term fuel trim 128
O2 .450v should cycle from 0.001 - 1.000v rapidly crossing the .450v
Cross Counts count of O2 voltage crossing above and below .450v
MAP Manifold Absolute Pressure (vacuum) sensor low vacuum adds fuel high vacuum subtracts fuel. 30kpa would be normal
CTS Coolant Temperature Sensor should match outside temp at first start of day and read over 180 *F. for operating temperature. Below 168* ecm will add fuel.
TPS Throttle Position Sensor should read less than .75v at idle. Voltage should rise smoothly to 5.0v at Wide Open Throttle.
Basics to look at. You might also look for U.S. car clubs for help.

Thank you, yes I do have the full Service manual ad have already looked at Section 6E, that is why I am gona try with the laptop to read data from the ECM, I will then try if I can identify any data that sticks out, I am only used to dealing with error codes such as Fx3, and airbag sensor. I greatly appreciate info from any other users that may have expertise on these issues. Incidentally I did have a new 'California' cat converter when it first failed, and thinking this may have been the problem I changed it back to the original one but it failed again pretty much with the same reading.

Thank you Kesova. I have taken a readind on TTS Datamaster at idle and full temperature and got: Integrator STF trim=.131, LTF trim=130, MAP Vacuum=35.1kpa, O2 volts=.115, fairly constant.
My money is in the O reading and don't think it is the sensor, as it is the second one and brand new, so combustion is running too lean which leaves 2% oxygen in the exhaust gases, and that is what failed the gas tests. The question is why the ECM is not correcting the mixture when it detects such low voltage from the O2 sensor.

I would follow dtc 13 and 44 charts. It's why is O2 not changing. Possibly local tech may have tip concerning O2 failures. INT/BLN is correct coolant temp. Is ECM actually going into closed loop?

Thank you, I have done a 10 minute continuous monitoring on Datamaster and at first sight cant find anything wrong, and the O2 data fluctuates very rapidly from .45 to .800 all the time, it seems the .115 I had quoted was just a one second snapshot. The car does go into Close Loop, and no DTC 's are generated, unfortunately there is no one that I can find in this region that knows anything about these cars, they are very uncommon. I am beginning to wonder it may have something to do with the 'Air Injection Reaction', System, it seems quite complex and does not seem to generate DTC' s and it sends air to both the exhaust ports and Cat convrter, so I am going thru a stratospheric learning curve, and if I cant fix the problem the car will have to be mothballed, a pity because it is otherwise in excellent condition. what complicates things is that I have no access to an exhaust Oxygen detector to be sure the problem is fixed, and the test station is quite far away.

IDK there is a American car enthusiast in Europe themed pages on Facebook.