exhaust leak= bad mpg?

will a cracked manifold cause a decline in mpg? I am getting 15mpg and only have 1.5 lift. cone filter also.

I only hear a small tick tick tick.

Hmm.
I hear that the AMC 4.0 loves its backpressure, in fact needs backpressure to operate at peak power and efficiency. I think an exhaust leak could have an effect on MPG but I'd be hesitant to attribute all your problems to that...
Do you know you have an exhaust leak or is this a guess?

Maybe too much temperature loss if it's a really big crack. If the O2 doesn't heat up you'll stay in open loop mode which uses more gas.

Many things can cause low MPGs, including an exhaust manifold leak!

yossarian19 said:

Hmm.
I hear that the AMC 4.0 loves its backpressure, in fact needs backpressure to operate at peak power and efficiency. I think an exhaust leak could have an effect on MPG but I'd be hesitant to attribute all your problems to that...
Do you know you have an exhaust leak or is this a guess?

Click to expand...

Whered you hear this? In fact I don't think it likes back pressure at all, no engine does, but some computers were designed with some backpressure in mind. However a small exhaust leak won't affect back pressure enough to really do anything at all, the only way it's going to change things is if you take off your muffler, say, and run straight pipe.

Also, a cracked manifold will definitely cause bad MPG. O2 sensor sees an influx of air and thinks the engine is running to lean, so it tells it to dump more fuel in.