Exhaust Gas Sampling - Ferrari Life

Exhaust Gas Sampling

Exhaust gas analysers can be very useful tools when searching for cylinder misfires, clogged injectors, etc. They give a more complete picture of how well your engine is combusting the fuel than a simple wideband AFR gauge can provide.

Unfortunately, unless you have a "hookup" for a performance chassis dyno equipped with a 5 gas analyser, it may be both difficult and expensive to find and use one of these tools.

Here is a reasonable alternative, if your state inspection stations are equipped with chassis dynos and/or tailpipe sniffers. At the heart of these sniffers is a sophisticated 5 gas analyser which can be adapted to sample exhaust gas at the exhaust manifolds (pre-cats), in order to determine how well the engine itself is combusting the fuel.

The end probe for the sniffer will look like a perforated muffler for a small lawnmower engine, and normally this can be unscrewed to reveal a male 1/4" flare fitting, better known as a -4 AN male to us hotrodders.

The Ferrari exhaust sampling ports are those gizmo's on the exhaust manifolds, covered with brass acorn caps. If you unscrew those caps with a 13mm socket, you'll find a male flare fitting with M8x1.25 threads. HOWEVER, if you then put your deep well 13mm socket on that adapter and unscrew it, you'll find the other end is a male M10x1.25 thread. So now you're left with a hole in your manifold that has M10x1.25 threads, and you need to get to -4 AN to match the inspection station's sniffer.

Earl's Performance Fittings to the rescue. Their 592045ERL fitting (see photo below), is a male M10x1.25 by male -4 AN. Install these into your exhaust manifolds in place of the Ferrari adapters.

Then you simply need a 5-6 foot chunk of 1/4" tubing, bent as desired (I bent mine 90 degrees at 16" and 90 degrees at 48"), put two flare nuts on it and flare the ends.

Now you can connect your engine directly to the 5 gas analyser at your inspection station, and all it'll cost you is what a normal state inspection costs, in lieu of hiring a dyno for $200 per hour. To be sure, you'll probably want to make one dyno pull for each sampling port (4 on a V12), but the dyno operator should cut you a deal for multiple runs :)

So what's the point of all this? Well, you want to try to achieve "perfect" combustion, which from the gas analyser's point of view means 13.5% CO2 or above, with less than 1% CO, and minimal (below 100 ppm) HC's. If you're not achieving these figures, then your car might be running rich/lean or just not as well as it should, and it's time to do a deeper diagnostic.

And why go through all this trouble of sampling at the exhaust manifolds - why not just use the tailpipe sniffer as it was intended? The catalytic converters, if they're present and working, are there to finish the combustion process, and they'll reduce the CO and HC's to nearly unmeasurable levels. So "sniffing" the exhaust at the tailpipe will not give you a good indication of how well the engine by itself is combusting the fuel - only how well the engine + the cats are doing.

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Created by cribbj , 10-10-2011 at 08:39 AM
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