06-16-2015, 12:37 AM
(06-15-2015, 11:09 PM)immgunn_imp Wrote: Why the need? Primarily fuel control. The CB's computer (powertrain control module (PCM)) is programmed at the factory to deliver the proper air/fuel ratio for the operating conditions. This is the programming. Programming assumes everything is in proper operating condition. As the CB ages, things go askew. Garbage in results in garbage out. The CB no longer delivers the proper air/fuel ratio for the operating conditions. This is where the oxygen sensor (O2S/HO2S) comes into play. The HO2S is calibrated for the air/fuel ratio of the engine it's designed for - generiocally - 14.7:1 (stoichiometry/lambda). Median HO2S voltage - generically speaking - 450mV equates to 14.7:1. As defects appear they affect the HO2S' median voltage. The PCM will deviate from the programmed fuel injector on-time to compensate bringing the HO2S back to it's designated median voltage in turn bringing the air/fuel mixture back to it's designed ratio.
Let's say the fuel pump weakens and fuel pressure drops. This will result in a biased lean air/fuel ratio. A leaner than desired air/fuel ratio will skew the median HO2S voltage low. The PCM responds to a low median HO2S voltage by increasing the fuel injector on-time from it's original programming. Adaptive fuel strategy, integrator/block-learn, short-term/long-term fuel trim. This is what makes modern vehicles so great. Why folks feel the need to screw this up by removing the HO2S is beyond me.
The PCM is supposed to monitor HO2S performance and illuminate the malfunction indicator light (MIL, check engine) when there's a problem. This doesn't always happen. Japanese manufacturers are hesitant to turn on warning lights. Warning lights upset customers.
HO2S' can be tested using a digital storage oscilloscope (DSO). Artificially manipulate the a/f ratio full rich (propane) and measure maximum HO2S voltage. Artificially manipulate the a/f ratio full lean (vacuum leak) and measure minimum HO2S voltage. Snap the accelerator engaging acceleration enrichment and measure how long it takes the HO2S to transition from lean to rich. Min, max, rate of change. Minimum spec is 0-170mV. Maximum spec is 800-1000mV. Rate of change (170mV - 800mV) should be less than 100mS.
TMI
Great educated answers. thanks for sharing!