You could with some of the OBDII gauges out there or an app on your phone.

The downside to the cali spec 4runners is that you have 2 cats (easy enough to get that fixed but still extra work, plus if you are in cali it won't pass smog if you remove one) They also have EGR, once again can't remove it in cali and pass smog. So for a truck that will be owned in cali a federal spec truck might be the best idea and just spend the money on a wideband gauge.

Or get a 2001-20002 federal spec 4runner, they also had the wideband sensor IIRC but didn't have all the stupid power robbing emission stuff.

 

My '99 is Cali spec emissions, but I have no EGR.

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Interesting, sure it is cali spec?

 

100% sure it's Cali spec. I have 2 cats, and a wideband AFR sensor on upstream side. My handheld scan tool also has a reading that says something like "Emissions Status" or "Emission Spec" (can't remember off the top of my head) and it returns a value of "CA", which I assume is for California.

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interesting, well then I guess some years came with EGR and others didn't.

 

And if you don't have an OEM wideband, $20 or so at a muffler shop will get another O2 bung welded on, then you can get a standalone WB gauge.