95 ZJ won't pass smog

[wgregt]

Got a friend with a 95 ZJ that didn't pass CA smog. The smog shop suggested a new cat and O2 sensor, which he did. Re-tested it, and it still failed, so the shop swapped the new parts off again.

Got any ideas on what else to check in order to pass the test?

 

[Jays siik xj]

Put new plugs in it and run a couple cans of seafoam through the engine and fuel... any codes showing up?