I have a 1986 Monte Carlo Sport Coupe with a stock 4.3 and a thm350 transmission. I know 4.3s aren't great on gas, but I'm only getting 13 mpg. It has a fresh tuneup, and the catalytic converter is the end of the exhaust. (the rest rusted off, i didnt opt for that)

Why is my mpg so bad? Any help would be appreciated.

 

Sorry 2 read that you are getting poor MPG's. Who did the tune up and what did they do...Could the cat still be clogged & restricting the flow of exhaust ?

Check the below link to see if it helps...You are not alone...Good Luck
https://www.google.com/webhp?sourcei...4.3L+GM+Engine

 

I did the tuneup. All Acdelco parts.
Dist. Cap
Rotor button
Plugs & wires
Oil and filter

I don't think the cat is clogged because the car still performs well. The only thing I've had happen is a small backfire while decelerating from 60 or faster. I assume that means it's running a little rich. I park in the same spot every night and warm the car up for 5 Minutes every morning, and where the exhaust exits, the concrete is a little blacker.

 

How many miles on your engine ? Has it every been rebuilt ? Valve Job ? Jet's replaced in the Carb ? Are you the 1st owner ?

I hope a member can help you. Check bad on your thread later & see what other member's post. Good Luck

 

It has 65,000 miles. I'm the 2nd owner, but I don't think it has ever been rebuilt

 

Thanks for your reply. That's super low miles for the year 4-Sure