I recently bought an old exhaust gas analyzer just like the one I had in the 70's. My old one got loaned out and never found its way home...... Anyway, this instrument(Penske)seems to go through the calibration regimen ok, but probably being 30 years old, I have to question its accuracy. Anyone got any ideas on how to verify the accuracy of the instrument? I have a couple of modern vehicles I could try it on, but both have catalytic converters of course and I don't know how this would affect the instrument. I think it is actually converting EGT into a fuel/air readout and I would think the cat would skew those readings. One of you engineers help me out here, please.
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Exhaust gas analyzer
Ed, would taking it to a state emissions testing center and testing on your auto with both yours and theirs be a viable option? That's assuming theirs is correct!
Charlie -
Re: Exhaust gas analyzer
The units at the inspection stations have a gas cylinder for calibration.Comment
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Re: Exhaust gas analyzer
I don't know about other states, but in Illinois the state testing lanes (actually a contractor to the state) will not allow that during business hours. The tests are so computerized that they can allow nothing to interfere, or chance to interfere, with the test.
I was involved in a course where we went to the testing station and got to operate cars on the dyno - it is harder than it looks. We had to do this after the lanes closed, and the link to the state computers was severed. If you could get into that kind of situation it would work, but not during normal business hours.
No harm in visiting the office and asking, however. They just might have a tour for students like I was involved in. Another option is a local vocational school- high school or college. Many of these schools have emissions testing equipment, and might be willing to do a comparison with your equipment if it fit with their course of study.TerryComment
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Charlie and Wayne, great idea, but this state does not do emission testing. I suspect that is much more of a blessing than a curse, unless older vehicles were exempted, of course.Comment
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Ed - most of those old inexpensive A/F ratio meters marketed to "consumers" worked on the basis of CO level. CO level is a very good surrogate for mixture ratio, but only on the rich side of stoichiometric.
At 12.5:1 A/F ratio, which is the "best power" ratio and also typically the best idle ratio for maximum idle quality on vintage engines, the CO level is about six percent. At stoichiometric, (14.7:1),which is what modern cars idle at when in closed loop mode (after they are warmed up) the CO level is near zero. Between these two A/F ratios the percent CO varies nearly linearly with A/F ratio.
Assuming this device works off CO if you test a modern car at idle that is fully warmed up it should read near stoichiometric (14.7:1), since that is what modern cars idle at and the fraction of a percent CO in the native exhaust will be an even smaller fraction of a percent after the converter.
EGT can be a surrogate for mixture strength, but you need a good known baseline to measure from and other variables such at timing affect EGT.
The problem with A/F ratio meters that key off percent CO is that they will only give useable results at richer than stoichiometric, so they are okay for setting up the idle mixture on a pre-emission car, but they aren't any good for mixtures near stoichiometric to leaner than stoichiometric because there is virtually no CO at stoichiometric or leaner. If this unit is portable it might give you decent results at WOT (like for setting up the FI power stop by doing WOT runs from 1500 up in third gear), but won't be of any value in setting up the economy stop, however, IMO the best way to set the economy stop is to keep leaning it until the engine just begins to surge at cruise, then tweak it slightly richer to get rid of the surge.
DukeComment
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Re: Exhaust gas analyzer
Well duke, you sort of read my mind. I was wanting to check the power stop setting on my FI, since I think it's just a tad rich. I think I have the economy stop just about right, but I get just a bit of smoke at WOT. Never can really tell if it's too rich a mixture or a bit of oil smoke. The engine has forged pistons and may not have the best oil control on the planet. I thought the exhaust gas analyzer might help me pinpoint the right mixture without going through quite so many trial and error adjustments.Comment
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Re: Exhaust gas analyzer
One other note. Years ago I used a small A/F ratio meter on my Cosworth
Vega that I borrowed from a friend. I think is was from Sears. It gave pretty consistent numbers at WOT of about 11.5, but I was never sure of the accuracy.
When testing on the road at WOT you have to be concerned with how quickly the instrument responds. About the best you can do is to accelerate from low revs to high revs in third or fourth gear, but you'll need a stretch of road with little traffic and no cops. Since it will take say 10 seconds for each run, I would hope that the instrument responds quick enough to give valid readings.
Let us know how it turns out.
DukeComment
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Re: Exhaust gas analyzer
years ago i had a sears in a green metal box that we used at the drag strip. the part that went into the tail pipe rusted away from the gases.Comment
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Re: Exhaust gas analyzer
It was probably all the additives that you used in the fuel that ATE the tip up, not the exhaust rusting it away. Not that a racer would do anything like that.Dick WhittingtonComment
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According to the NJ DMV radio ads...
Or maybe it was the Twilight Zone. All new vehicles sold in NJ starting in 2001 require inspection each 4 years.Comment
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Re: According to the NJ DMV radio ads...
Dave: I have a 2003 purchased and inspected by ther dealer in September 2002 and the dealer inspection sticker on my car calls for reinspection in september 2004. The car was brand new when purchased.Comment
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You gotta listen to the radio more often...
The Philadelphia area radio stations ran the PSA, with the NJ Governor's own voice (grandstanding, I think) until I was sick of hearing it. Follow this link to the land of inspection insanity.
NJ Department of Motor VehiclesComment
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