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Old 04-07-2005, 11:41 AM
Duke2.6 Duke2.6 is offline
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Join Date: Mar 2003
Location: Southern California
Posts: 2,272
Originally Posted by LeaUK

An interesting and well written post, thanks for the link. However I still have three questions:

1. Is the purpose of the diag signal to allow visibility of the adjustment (whether richening or leaning) the system is making compared to the 50% base?

2. How to read duty cycle for this diag output?

3. Does residual O2 in the exhaust lead to increased CO too?

I think this thread answers 1+2 (thanks guys) but can someone confirm.

Much appreciated.
I don't know what you mean by "diag signal".

A stoichiometric mixture should result in "engine out exhaust" that contains a small concentration of HC, CO, and O2 plus some NOx. A three way catalyst requires this exhaust constituency to provide both oxidation and reduction reactions. The amount of 02 in the after converter exhaust is a good diagnostic tool. If it is zero, the catalyst is operating at maximum efficiency by using all the available O2 to oxidize HC and CO. A tenth of a percent or more indicates that full catalytic oxidation reaction is not being achieved. This is often due to the converter being too cool, and these KE-equipped engines seem to be particularly suspectible to catalyst cool down by improper conditioning prior to testing such as shutting the down before the test or excess idling prior to the test.

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