Here’s a weird one. Just had a muffler shop install a new magnaflow, which Magnaflow says is the right option for the truck. However, now at highway speed, it drops out of 8th into 7th and is squashing my mpg. Caveat, I have a truck camper in the bed of the truck, but I had zero issues (other than bad mileage) the day before. All the sudden, the truck just won’t cruise in 8th. The Magnaflow guy said perhaps to reset the shift points by disconnecting the battery. Anyone have any thoughts on this? Since the truck “learns” how you drive?
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New Magnaflow muffler, rpm issue?
- Thread starter BigZman01
- Start date
H3LZSN1P3R
You're doing it wrong
You can try a reset im not sure if it will help but if the factory muffler created more back pressure than the new muffler it would make sense the drop in milage as you would lose a bit of low end TQ
jetrinka
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Weird I never experienced anything like that after I installed my Magnaflow. Mileage didn’t change at all and shift points/power level stayed the same. Are you sure you’re just not now hearing/feeling the MDS activating now? That became more apparent for me with the muffler replacement.
H3LZSN1P3R
You're doing it wrong
If he is carrying a truck camper around always im sure he is almost never hitting MDS
Crusty old shellback
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Possible that something got in the exhaust/muffler when/before it was installed?
If it's a gas motor, may be possible they messed up the cat.
Had an issue with a cat that the insides got broken. After it heated up some, it would basically clog and I'd loose all power. Once it cooled, it ran fine it it got heated up again.
If it's a gas motor, may be possible they messed up the cat.
Had an issue with a cat that the insides got broken. After it heated up some, it would basically clog and I'd loose all power. Once it cooled, it ran fine it it got heated up again.
I think perhaps it’s torque related. I just wondered if there might be another idea. It’s a pop up camper, not a hard side, so not that tall. When driving with the wind, it seems fine. When going up a slight pitch, it’ll just shift down. I’ve even messed with the auto-gear selector buttons on the steering wheel, and it still wants to slip down to 7. The tow/haul mode is worse, it goes to 6. I’m going back to stock and see what that does.
jetrinka
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True I didn't catch the camper thing. I'd hope he was in tow/haul mode disabling MDS with a camper on anyway.
OP - the conditions are all the same? No headwinds or inclement weather? I find personally I am super aware after anything is done to my truck and get sensitive to things I would not have noticed before.
Also what exhaust? Was it the direct fit muffler from Magnaflow? A catback system? A welded in muffler? What exactly was done? To my knowledge Magnaflows cannot be put in backwards like some other mufflers out there.
Rockcrawlindude
a rock crawlin’ dude
I believe it. I can’t explain why but I’ve experienced similar.
I had an exhaust system built in my tundra and the guy suggested magnaflow. It was a dual system with one muffler, very free flowing and sounded good. He showed me a cross section of the muffler it was a dual in dual out with a sort of X pipe built in.
But, the torque curve of the truck was totally different after. I felt like i lost a bunch of low end. It’s hard to tell by seat of the pants and maybe I’m crazy but I never touched a magnaflow again.
I had an exhaust system built in my tundra and the guy suggested magnaflow. It was a dual system with one muffler, very free flowing and sounded good. He showed me a cross section of the muffler it was a dual in dual out with a sort of X pipe built in.
But, the torque curve of the truck was totally different after. I felt like i lost a bunch of low end. It’s hard to tell by seat of the pants and maybe I’m crazy but I never touched a magnaflow again.
jetrinka
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Exhaust is a subject that’s always fascinated me. Performance header primary size, length, design (4 - 1 or tri-y) has always made sense to me in terms of what typically works but muffler design eludes me. Flowmaster for instance claims on their websites good torque gain just from a muffler change. I can only assume it may help scavenging from the engine but never understand how. Then there are straight through designs like Magnaflow which according to many butt dynos seem to move power up in the band.
Most people aren’t dedicated enough to to do before/after dynos with such things though. Even if they don’t produce more power it’s interesting to see how the power band changes.
Most people aren’t dedicated enough to to do before/after dynos with such things though. Even if they don’t produce more power it’s interesting to see how the power band changes.
Chris85xlt
Member
Ive experience something similar in past vehicles with flow through style mufflers. Under full throttle situations it suppose to flow for better power but seems to lose low end torque especially when cruising on the highway.
Ive had good luck with chambered style mufflers like Flowmaster and Spintech without losing that low end torque. my 0.2
Ive had good luck with chambered style mufflers like Flowmaster and Spintech without losing that low end torque. my 0.2