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| exhaust fell off and is better MPGs | |
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| Tweet Topic Started: Mar 5 2014, 08:25 PM (1,845 Views) | |
| 702852 | Mar 5 2014, 08:25 PM Post #1 |
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So I got my 91 3/5 3 weeks ago and the owner had the muffler in the backseat. Under the car was a bent piece of pipe at approximately between the front seat and rear seat with no muffler or anything... The cat is there though before the added pipe. I drove the car home and was getting 42 mpgs even with a check engine light saying "EGR" So...to pass my echeck and not get a noise level ticket I bought two pieces of pipe and re-attatched the muffler with some clamps. I didn't even muffler tape or jb weld it. The downside is my mpgs went down to 30/33 The other day the muffler came off and was dragging on the ground. I pulled off and put the muffler in the back seat. Then the other two pieces of pipe came off as I drove within the next hour or so and the car got back to as loud as it was before.... BUT the mpgs went up to 40 again. So does anybody have any pictures of their factory exhaust on their 3/5??? It should get fixed, but if I don't like how it looks/bends then I will have to figure something else out. |
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| 702852 | Mar 5 2014, 08:31 PM Post #2 |
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Edited by 702852, Mar 5 2014, 08:34 PM.
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| RONNIEREDLINE | Mar 5 2014, 08:57 PM Post #3 |
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METRO MAD MAN
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id say something is wrong with your oxygen sensor or it is mis reading because of your exhaust system. the oxy sensor has a whole lot to do with milage. to clean an oxy sensor, a cousin of mine who runs mc cluckey chevy, he told me to put your car in a lower gear and drive it at a higher rpm till you get the oxy sensor and the exhaust good and hot, then shift back up to normal and drive to cool it back down. this has worked alot of times for me and him as well at the dealer, but they replace the sensor at the dealer after this test. you catylitic converter has alot to do with milage as well. you have altered them both with a bad exhaust system. just letting you know redline |
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| RONNIEREDLINE | Mar 5 2014, 09:00 PM Post #4 |
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METRO MAD MAN
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stick with the factory exhaust as designed, they designed the motor, and the car it is in. they know more than we do about the whole system of milage,motor and body of the car they had engineers design it, we arnt engineers and if you alter from the factory design, then prepare to suffer the result. always keep the factory design, unless this is some sort of hot rod, which it isnt. just letting you know |
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| rmcelwee | Mar 5 2014, 09:27 PM Post #5 |
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I would say that the factory exhaust will give you better mileage than no exhaust. The snake oil salesmen have led most of the public to think it would be just the opposite but it is not. Last exhaust I built (compared to what I took off). It dumped out right behind my butt - mileage was not the reason:
Edited by rmcelwee, Mar 5 2014, 09:27 PM.
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| perfesser | Mar 6 2014, 12:42 AM Post #6 |
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Elite Member - Former Metro owner
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It's an interesting theory, but based on my 30+ years in the auto industry, I can tell you it just doesn't work that way. Engineering designs the product to function, and then the bean counters step in and ask them to "revisit" some of their design decisions in the interest of meeting cost targets. And the designers want to change the pure engineering design to better fit within their physical packaging constraints. On a car like the Geo Metro, the pressure is intense to meet those targets, and the compromises in the design are many and significant. A car like ours is not a pure design. The exhaust isn't designed for best efficiency any more than the rear seats are designed for best long-term comfort. Any reasonably competent mechanic or engineer can figure out a better one for less than a couple of hundred dollars, but the factory wasn't about to tag that cost onto the MSRP in an extremely price-competitive market segment. The stock exhaust is a compromise, suitable to do a lot of things well, but nothing really well. You can optimize the design to achieve whatever you want and tailor it to your requirements as long as you're willing to live with your own compromised design. Noise level, mpg, power, etc. can all be targeted, but you can't have them all with the same design. The factory exhaust works for what it was designed for. That doesn't mean that a group like GMF can't redesign it to do other things better than stock. |
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| 702852 | Mar 6 2014, 08:20 PM Post #7 |
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ummm... well where is the oxygen sensor on the 91?? before the cat?? after? |
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| 702852 | Mar 6 2014, 08:21 PM Post #8 |
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And if the O2 sensor was missing wouldn't I have a check engine light for it? |
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| perfesser | Mar 6 2014, 10:02 PM Post #9 |
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Elite Member - Former Metro owner
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On my '91 hatch, the O2 sensor is on the left side of the exhaust manifold below the heat shield. The wiring for it snakes across the valve cover from the rear. |
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| pcthurman | Mar 14 2014, 06:57 PM Post #10 |
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New Member
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simple cat is bad........ |
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| 702852 | Mar 19 2014, 08:03 PM Post #11 |
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The cat is still on there. if it was the cat. the mileage shouldnt have incresed by 10mpgs. |
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| Johnny Mullet | Mar 19 2014, 08:50 PM Post #12 |
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Fear the Mullet
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I have seen resonator pipes and mufflers clog up from the material that came out of the cat. |
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| me2 | Mar 19 2014, 10:16 PM Post #13 |
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So Perfesser, do you have an opinion on how you would change from the factory exhaust design to improve mpg? Of course my guess would be a system that is less restrictive. I don't have any local authorities micro-managing how I run my car ( unlike so many of you) so assume I could do anything I want. Well, because I actually can. |
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| perfesser | Mar 20 2014, 01:08 AM Post #14 |
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Elite Member - Former Metro owner
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I haven't even looked at the exhaust yet, but there are a bunch of guys here who have done extensive experimentation on the subject. Shouldn't be hard to find a few dozen threads on them. Good luck! |
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| Woodie | Mar 20 2014, 05:44 AM Post #15 |
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