DIY Replace Back Muffler / Resonator with Straight PipeSubject: DIY Replace Back Muffler / Resonator with Straight Pipe Title: Increase Fuel MPG by Replacing Back Muffler Overview: When your back muffler fails, and or if you want a bit more gas milage, replacing the back muffler with a straight pipe seems to work fine and increase MPG. This is much cheaper than purchasing a back muffler with DIY or to have a local customer shop install a straight pipe. Symptoms: Back muffler failing, onion peeling and / or holes in the back muffler. Experience Level: Medium Tools Needed: Hack Saw, Ratchets, Wrenches, etc. Time Needed: About 1 hour: Parts Needed: Pipe parts from local auto store. Exhaust sealers, hangers, pipe tip (stainless) Procedure: Remove the back muffler by cutting the pipe before the muffler about 2 inches in front of the muffler. Replace with straight pipe components or have a shop do it. You will need some time to get it 100% right. It took me a couple of tries. Outcome: - Money savings in replacement. - Slightly louder, but not much. Actually a better sound (subjective) - 1-5 MPG gas savings, especially on open road. Discussion: I have done this on a 99 9-5 I4 for about 1 year now and it seems to be working fine. I am getting about 3+ MPG on the open road since this was done. It is an automatic with 140k miles solid 29-30 MPG with regular fuel on the open road. I really do not see the need for the back muffler / resonator at the present time. I will be doing this on a 2001 V6 wagon soon. The muffler will be failing soon.
Starting from the front, coming off the exhaust manifold should have, 1. Exhaust pipe, 2. Catalytic converter, 3. Exhaust pipe, 4. Resonator, 5. Tail pipe. Also, there should be an Oxygen sensor somewhere around the catalytic converter.
Possible results are , increased fuel use, reduction in power and you may fail noise emissions (too much noise), some after market exhaust systems are designed to give improvements but these are general much more costly than standard fittings. I would not be happy myself and would want it put right, Not sure which country you are in so can't advise on trading standards, but in uk items must be fit for purpose or you get your money back.
Yes, the muffler should be upstream of the resonator. In other words, from the engine, you have the catalytic converter, then the muffler, then the resonator is last, near the tail pipe. Possibly they installed the wrong muffler or resonator. The muffler will have the most effect on the sound you hear.