Failed emissions, high HC and NOx.

[GTOger]

Originally Posted by scottfab

It'd be helpful to know what diag tools you do have.

Oh, I have a couple of OBD-II cables and various pieces of software to use them. But I don't think that'll do me any good on this OBD-I car. What I ought to do is poke around and see what folks are recommending. I know the car will tell you exactly what's going on if you can ask it.

[Marc Haibeck]

A shop that advertises that they like to perform emissions oriented repairs will have an exhaust gas analyzer. Measuring the exhaust gas before the catalyst is not commonly done. They will need to weld a fitting on the pipe going into the catalyst.

For good emissions performance there is little tolerance for a misfire. The engine needs to be able to idle silky smooth. If not it should be investigated.

Note that a technician with a gas analyzer can probably give you good advice as to how the car will do on the next test based on the emissions readings, in the shop. This way you can verify that a repair is effective before going to the test.

[GTOger]

Thanks Marc . OK, I guess I better try a bit more diatnostic work. The engine seems to idle very smoothly to me. Then again, my daily drivers include a 3/4-ton GMC diesel and a 5-cyl twin-turbo Volvo. They're "smooth" in their own unique ways, which leaves the LT5 to really feel like butter! LOL.

I have a really good mechanic here locally. He's never worked on the ZR-1 - it's always gone to Corey. But that's a 5 hour trip and still no gas analyzer.

[curtsvette]

had the same problem the last 4 years . my 91 fails emissions bad . if i siphon out all the old gas and put in fresh gas it passes with flying colors. Its the ethenol in the gas. doing additives didnt help have to get all the bad gas out and new gas in to fix it. I just do that every year to pass. only 3 more years to have to fool with emissions in Texas luckily

[Z51JEFF]

My car failed a few times.I replaced both 02 sensors and put in 5 gallons of E85 and it finally passed.Not looking forward to the next test.In Ca they keep lowering the MAX levels allowable.My car with 6000 original miles wouldn't pass the current levels which are 502 MAX Nox,at 6000 miles the car had a Nox level of 702.Ca keeps lowering the MAX limits.