Remember, the O2's are the tattletales. The post cat should be cycling the same as the front O2, but just until the cat gets hot and starts working. This has to reach at least 600 degrees-F. Running in the shop it is almost impossible to get the cat working properly even when raising the RPM.
Take it for a normal drive for about 20 minutes.
Monitor both the pre-cat and the post-cat sensors right from cold start.
Also monitor the STFT an the LTFT.
Coolant, TPS & MAP as well.
Near the end of the road test, go to a very quick large throttle opening for a few seconds, then back off the throttle for an extended decel. The O2 responses should be quick, but unless you use a scope it would be hard to see a 100-ms response time, but you might depending on the number of frames per second the scanner is capable of.
The front O2 is the primary fuel control feedback with the post-cat the monitoring sensor for CAT capability. SOME Chryslers will also use the post-cat for fuel control to "try" to protect the cat so careful observation of the O2 sensors activities under varying throttle & load commands can tell you a lot.
As for back pressure, at idle it should be 0 to at most 0.5 psi. At a park or neutral steady 2000 rpm, it shouldn't be anything more than 2.0-psi MAX, and I mean MAX. Most healthy unrestricted cats are only 1.0, 1.25, 1.5 psi at 2000 rpm.
A vehicle that adds 8% fuel is a lot. Yes it's a long way from 25% where it would code but most vehicles will be running just under, or subtracting on the LTFT. That's provided it's not running bilge wash for fuel.
Take it for a normal drive for about 20 minutes.
Monitor both the pre-cat and the post-cat sensors right from cold start.
Also monitor the STFT an the LTFT.
Coolant, TPS & MAP as well.
Near the end of the road test, go to a very quick large throttle opening for a few seconds, then back off the throttle for an extended decel. The O2 responses should be quick, but unless you use a scope it would be hard to see a 100-ms response time, but you might depending on the number of frames per second the scanner is capable of.
The front O2 is the primary fuel control feedback with the post-cat the monitoring sensor for CAT capability. SOME Chryslers will also use the post-cat for fuel control to "try" to protect the cat so careful observation of the O2 sensors activities under varying throttle & load commands can tell you a lot.
As for back pressure, at idle it should be 0 to at most 0.5 psi. At a park or neutral steady 2000 rpm, it shouldn't be anything more than 2.0-psi MAX, and I mean MAX. Most healthy unrestricted cats are only 1.0, 1.25, 1.5 psi at 2000 rpm.
A vehicle that adds 8% fuel is a lot. Yes it's a long way from 25% where it would code but most vehicles will be running just under, or subtracting on the LTFT. That's provided it's not running bilge wash for fuel.
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