Major restriction problem is not the cat back, but the cat forward. Law says you can't fool with that, even a $25,000 fine if caught.
Culprit is the O2 sensors that really have not been improved over the last 30 or so years, response time it way too poor, while an average stoichiometric ratio is attempted to be maintained. It does this by running the engine 50% lean at the time, and rich the other 50%. Difficult to reach over 6 corrections per minute.
When running lean, takes it toll on the exhaust valves, when rich, the cat over heats plugging it up over time. Then the O2 sensors are worthless until the engine reaches operating temperature that is never done with short city trips. PCM is in open loop mode. Do have adapters that replace the O2 sensors to test the exhaust pressures due to a partially plugged up catalytic converter with specifications. And as O2 sensors age, their response time also decays.
With better diagnostics, when the pulse rate declines will set the CEL code, but for years, many vehicles did not have this feature.
In brief, playing around with the cat back is next to worthless, cat forward is where all the problems are. And only the law can change this. The cat always has been an after the fact type of emission control and has been this way since 1972. One key solution to this problem is to remove the C from HC's, but our congress won't buy this. Some odd 42 years later, just thinking about it.
Culprit is the O2 sensors that really have not been improved over the last 30 or so years, response time it way too poor, while an average stoichiometric ratio is attempted to be maintained. It does this by running the engine 50% lean at the time, and rich the other 50%. Difficult to reach over 6 corrections per minute.
When running lean, takes it toll on the exhaust valves, when rich, the cat over heats plugging it up over time. Then the O2 sensors are worthless until the engine reaches operating temperature that is never done with short city trips. PCM is in open loop mode. Do have adapters that replace the O2 sensors to test the exhaust pressures due to a partially plugged up catalytic converter with specifications. And as O2 sensors age, their response time also decays.
With better diagnostics, when the pulse rate declines will set the CEL code, but for years, many vehicles did not have this feature.
In brief, playing around with the cat back is next to worthless, cat forward is where all the problems are. And only the law can change this. The cat always has been an after the fact type of emission control and has been this way since 1972. One key solution to this problem is to remove the C from HC's, but our congress won't buy this. Some odd 42 years later, just thinking about it.
