Dear friends, I have a beautiful 1988 Corvette that runs flawlessly in all senses, BUT, since I purchased it years ago, it has ALWAYS had problems in the emission test.

Meanwhile the CO and CO2 values are OK, the called "lambda factor" is too high (1.2). Until I know, the lambda factor is the proportion of the fuel/air mixture. Values over 1 mean that the mixture is poor (too much air). So my Vette has too much air on the mixture, it seems.

Now, let me tell you that I have replaced the spark plugs and its cables, air and fuel filter, injectors, EGR valve, catalityc converter, mufflers, rear y-pipe (front seems ok)... Also, it is supposed that the O2 sensor was replaced also, but this is the only part that I never bought and was teorically replaced in the workshop, so I am not sure. These parts have been replaced during the last 5 years, but the car has had very little use, and I repeat that the high lambda factor returns every year, always with the same value of 1.2 since the first time...

Now I intend to order a new O2 sensor just in case, and also the EGR solenoid valve and tha cable that connects it. Will this change anything at last?????

Honestly, I do not know what more can I replace or do. Maybe the hoses, but they seem ok.

If you have any idea or know how can I reduce the lambda factor, any help will be very much appreciated. I am tired of always beg the inspector to let the car pass the test, year after year :-(

 

If you can scan or take a picture of your last smog test results paperwork as well as what state your in would greatly help us to help you determine what's possibly wrong with your car.

 

tps Voltage At Idle? What's Timing Set At? Does It Run Rough? CTS Value On Scan Tool When Hot? Fuel Pressure At Idle? Fuel Pressure At 2k RPMs? What Are Your BLMs On The Scan Tool?

 

Not likely as the ECM does not call for EGR till steady speed for a while and an EGR leak would be detected by the ECM at startup.

Indeed the above requested info would be very helpful in diagnosing the emissions issue.

If CO & CO2 are ok I can't see how they determine "too much air"???

In any case a scan of the ECM would likely shed much light upon the issue.

 

If they used wideband o2 sensor, narrow band o2 sensor, or an emissions analyzer. The emissions analyzer would detect too much nitrogen oxide, which would indicate a lean fuel mixture.

 

My country is Spain, not the USA, so I do not know if the emission test is the same. I also suspect that the high lambda factor (lean fuel/air mixture, at least in theory) is due to high presence of Nox. That's the reason why I thought that a replacement of the EGR valve will fix it... but nothing has changed ever. That is the reason also why I am thinking on a solenoid replacement.

In any case, I will try to read pressures and voltages and let you know. Thanks!

 

I had a very similar issue with my 95 and NOX.

Pull the O2 sensor and place a pressure gauge in the bung. Many vacuum gauges are also pressure gauges. With the engine running, measure the amount of back pressure. Mine read very close to zero. The EGR on the 95 needed some back pressure to operate correctly. What was happening is that it would just start to open, but the lack of back pressure would immediately close the valve. So the EGR was not doing what is was supposed to by opening and moving exhaust gasses into the cylinder to cool the cylinder and stop the creation of NOX.

I ended up having to put in restrictions in the exhaust pipe. I necked the pipe down from 2-3/4" right before the muffler to 1-1/4". That resulted in 1 pound of back pressure and the EGR worked and brought the NOX down.

 

I assume this is a performance engine, vs stock?

If it was stock, the damned thing would pass smog in any country in the world. Period.

What mods?