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what about my cats?
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texasdanml430 Offline

Posts: 68
Joined: Mar 2008
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Post: #1
what about my cats?

dumb question Nr 978:

i thought catalytic converters were supposed to see stoich. a/f ratios to work efficiently. If i get my engine to run leaner in closed loop, will it ruin my cats? does anybody monitor exhaust gas temps to make sure you dont get carried away with too lean mixtures?

i really like your ideas. had toyed with the idea of using just a c-cell and voltage divider to float an extra .15 volts across my o2 sensors to fool my ecu to run leaner. but some other wide band o2 gurus told me the ecu look at o2 inputs LAST in fueling algorithms in closed loop.

even thought of trying a wb o2 with programmable narrow band outputs to feed my ecu, but they're still pricey.

have found some swamping resistor values for ect and iat that seem to work, though only briefly, as the ecu seems to compensate.


dan in texas

my motor is a mercedes benz v8 in an M-series suv. 4.3 litre. getting real tired of 15 mpg, but dont want to fry the thing, as its a great truck for towing my 5000 lb boat and trailer.
03-27-2008 01:11 PM
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mike Offline
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Posts: 2,023
Joined: Jul 2007
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Post: #2
RE: what about my cats?
First of all the question(s) are not dumb. But none the less there are way more than one question and they should've been numbered 978-984. Big Grin

The cat converter is basically improves the quality of the exhaust through a catalytic process. If there's less hydrocarbon in the exhaust it will catalyze less, but will not be adversely affected by this.

Monitoring exhaust temps is really not necessary with the EFIE. It has a built in safety factor in that it will drive the ECU into open loop before it can lean the mix to dangerous levels. But if someone were leaning their mix by several different means, and not actually adding a combustion improvement technology, this could become an issue.

Wow, I don't know what "gurus" think the sensor data is used last, but that doesn't even make sense. The amount of gas in the mix is the first datum you would need to know to then determine if more or less was needed. The EFIE reportedly works on wide band sensors, by the way, but is known not to work with AFR (Air Fuel Ratio) sensors.

You might read Tuning For Mileage. It covers tuning the various devices, and covers the factor of the ECU compensating for changes. Basically if you cover all the bases in that article you should have the ECU at YOUR mercy, not the other way around.

Good luck with your project.

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03-27-2008 05:06 PM
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