Today I made the yearly "sniffer" test we have in Sweden. I whas a bit worried as I have change so many things on the car since last year. BUT im a bit confused about the results. Lets start with my engine before the questions. Vette -91 CSB355 9.8:1 comp All forged internals. Converted LT1 intake. 1:6 rrs Full length headers, dual 2,5" with metallic race cats. LT4 hotcam JEGS Canfield 197cc heads Malloy 6al ign box 6 spd manual I tune the car myself, and im between 122-129 on the L-term BLMs. The "sniffer" test here is first at idle, then "raised idle" to around 1500-2000rpm. With everything hooked up my HC whas way to high. HC: 350 ( 100 ) In other words, I did not pass. BUT, what I did then, whas to Disconnect the EST. To get only base timing ( 8 degrees ). And the results where astonishing. HC: 020 LAMBDA 1.02 So with this, I passed. ( This is even better results then on my Audi community car ). With the EST connected I use 25 degrees at idle rpm, closed tps tabel. And the car seems to like it, well atleast the drivability is good and idle is stabel. But what can be wrong here? Throw me a bone on what to look for. I havent got a clue. Could my base tming be off? Im glad that I passed the test, but im also whery confused with the results. Thanks Anders

Cold cat? Did you have the engine running quite a while before the test, and let the RPM stay high a while before sticking the probe in the pipe? Running low timing has several benefits for an emission test - hotter exhaust = hotter cats, later timing means quench areas are exposed when the flame finally arrives, hotter exhaust = more afterburn, all reduce HC well and a little bit CO.

I think you wrote down the CO wrong, but not sure. Is it supposed to say .4 and .35 %, or is it 4% and 3.5%? Option A means just high HC, option B means it's running very very rich for what should be a closed loop system.

Thanks for the answer.

Coolant temp where 208 degrees Fahrenheit. I made several high rpm runs before I drove in to do the test.
Im sorry about the numbers, I wrote those wrong, I dont know what I got those numbers from?!?
Right now I cant fint the document, I get back to the exact numbers for CO and CO2500.
BUT what I remeber is, that HC whas the thing that stood out.
At idle I hade 350HC and at 2500rpm 170 HC.
And the trend whas that if we increased rpm the HC got better, and as the HC got better all the other values got better as well.
But we couldent get under 170.

And then when I disconnected the EST, the idle RPM droped, SES light came on, and the HC value just dropped like a stone.
Aswell as all the other values. And HC stayed on 20, both at idle and at 2500rpm.

Another thing, can it possible be a leaking intake gasget, that make the 02 read "wrong" ? I got a tiny amount of bucking at low rpm/low map. That I havent been abel to tune out 100%. Perhaps its related?
Thanks..