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Jeep CJ Not Passing Smog


Topic starter

Hi Scotty,

I am pretty much done restoring my late grandpa's 1978 Jeep CJ7. It's a 4.2 inline 6 with a 2 barrel carb but it won't pass smog. It's a 4.2 inline 6 with a 2 barrel. Sadly for me smog exempt here in California is '75 and older. My dad told me that my grandpa was trying to find a vacuum leak before he passed. If that's the case where should I start. Anything else that you think would be causing it to not pass smog. I've been learning as I go and well this is my last hiccup. Any help you can give would be greatly appreciated.

-Greyson K

What exactly did it fail during the smog test? It should be in the paperwork.

3 Answers

Yeah they can feel smog for many reasons I need to live data but if you think it has a vacuum leak do my video finding engine vacuum leaks with a cigar


Get a can of carb cleaner and spray it on all vacuum hose connections and around the intake manifold with the engine idling.  If there is a vacuum leak, you'll hear the engine increase its RPMs.


I've worked on those engines in 1970s-vintage AMC cars. The emission control systems are extremely crude. There is no feedback like on a modern car for the system to keep itself in adjustment and compensate for wear, and no live data or data of any kind for diagnostic purposes. There is no computer and for that matter no engine electronics aside from the ignition, which is a standalone "dumb" setup. (A 1978 model even predates the computer-controlled ignition and feedback carb setup that AMC used in the 1980s.)

It could be difficult to get through aggressive smog tests like California's even back in the day. Over 40 years later it's a real challenge. As others have said more details are needed on exactly what failed. (Looking for vacuum leaks as described is a good start.)