i have a 1985 jeep wrangler with the amc stright 6. it runs good but its old and doggy and sucks on gas. i found a v6 3.1 low miles for $100 i want to swap these two. has anyone ever heard anything like this?

go from a 4.2l to a 3.1l?:confused: you think your jeep is a dog now, let us know how that little 3.1 pushes it.:shaking: just because something is cheap does'nt mean its the right thing to do.

That's all wrong, NOBODY puts a smaller engine in there jeep, unless you don't do trails, in that case you shouldent be on this site.

This is what you do,
Get a Chevy small block, Bore it, Stroke it, Back it up with a 700R trans(you going to have to cut your trans tunnel bigger) An atlas twin stick and D60's front and rear.

But to answer your question, I have not heard of decreasing the value, the power, just to put a crap engine in your jeep!

Stick with the engine you got and for $450 you can get a fuel injection unit that will ad 3+ miles to the gallon.
Never heard of a 85' wrangler?!?!?!