258 / 4.2 question

hunterdan

hunterdan

Well-Known Member
Joined
Apr 13, 2009
Location
Morganton,NC
I have been doing a tune up on an 87 YJ with the 258 carbureted engine. I had just driven it for 20 minutes and popped the hood to do some more tinkering. I noticed some smoke...more like a white vapor. It was coming from the air cleaner right where that metal corrugated pipe rises up from the exhaust manifold and feeds back into the air cleaner. There are two vacuum operated circular valves right above where the pipe attaches on the underside of the cold air intake section. No smoke anywhere else and seems to run pretty good. Any ideas what it could be?

Thanks, Dan
 
That's the air injection system. The air control valves are probably stuck open and are letting exhaust flow into the air cleaner under conditions when it shouldn't. Or the controls are making the valves open when they shouldn't, same result. Either way, you shouldn't have flow in that direction at idle.
 
Thanks for the help. I just see the vapor when it's just been driven and engine is off. I'll check the valves today and see if they are stuck.

On a different concern; If I get rid of the vacuum emissions stuff would this 258 get improved mpg and performance?
 
hunterdan said:
Thanks for the help. I just see the vapor when it's just been driven and engine is off. I'll check the valves today and see if they are stuck.

On a different concern; If I get rid of the vacuum emissions stuff would this 258 get improved mpg and performance?
Click to expand...

Can't speak from experience on the later 258s, but the early 80s 258s respond well to removing all the emission stuff, and running hei or nutter bypass ignitions and ford 2100 carbs. Just make sure you can tune up the carb without all that extra stuff on there. Ditching the carter bbd carb and vacuum rats nest, made a noticeable difference in my 84.
 
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