In FL, they used to just stick the sniffer in the pipe and a minute later you left.

Here in NC, after your car sits on a lift for 30 minutes and your temps go to 260F, they stick the sniffer in the pipe and then rev your car to about 2500 rpms while it takes the reading.

Why do they do this? I am contemplating on which springs to use in my HEI to determine when the advance in timing comes on. Would it be wise to have more timing sooner (ie- at 2500) or later (ie-at 35-4000)?

This would be a temporary thing done only to pass the e-check better and I will go with the looser springs for daily performance.

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock... all the suspension stuff... 9-bolt posi disk is in... K&N filter... 93 octane...

-=ICON Motorsports=-

 

Bio,

It is generally a good idea to keep the engine as hot as possible during an exhaust gas anaylsis. Revving the engine assures that the oxygen sensor is hot and the ECM is in closed loop mode. This will allow for lower emissions, so it is not necessarily a bad thing.

As far as the timing goes, more advance under light loads (like revving in neutral) shoudl provide more complete combustion and lower emissions. The only possible effect is that NOx will rise due to hotter combustion temperatures, but if the EGR is functioning properly, the emissions should be within limits.

So, did you fail? What were the readings?

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

They do that because emissions-theoretically that is where cars rpms spend most of the time in. They want to see what pollutant levels are during "normal" operation in city driving.

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George P. Lara
1994 Z28 LT1 T56
1984 Z28 High Output
Member: SCCA, SCFB, SC3GFB
Chevy Info --> MadMike's

 

Vadar, last year I passed with flying colors... at least the levels portion. I didn't have a stock air cleaner with the TAC sensor and my rear tire was a little too bald. It sucks having to put 300 things back on only for the one afternoon of testing.

The only thing is, that was with my q-jet and everything hooked up. I am replacing it with a Holley because something is stuck in one of the passages in the base among other problems, so the ECU is going to be bypassed. I am just wondering if I should add HEI advance springs on my ever-growing list of things I need to swap for the testing...