Tom,

1986 was the change year for several emissions parts on the 4-cyl. The exhaust manifold has a pre-cat inside, and is likely the problem you're trying to diagnose. On a trip from Phoenix, AZ into Riverside County, CA, our first Montero (April, 1986) plugged up and started to boil the pain on the hood. I pulled over at Chiriaco Summit and the engine was starting to misfire and load up. I shut everything down, waited about 20 minutes, had a soda, fired up and drove the last 75 miles home. Upon inspection the following morning, I discovered the manifold had melted away, blowing exhaust out just above the secondary air inlet tube. All the adjacent hood insulation had burned up, the underside hood structure was scorched, and I needed some parts quickly for my wife's daily driver.

A new manifold was $300 (ouch)!! Our monthly payment was only $75. So, I replaced the muffler, cat, and manifold. Solved all the problems, ran better, return 20 mpg rather than 14-15, and felt zoomier.

My advice, check the pre-cat and cat visually, as dT (fhuzz) had me do for a convertor I sent him. If you can see through the unit, it's probably ok. If you can't, then replace it.

Good luck!!
Russell <img src="/forums/images/graemlins/smile.gif" alt="" />