2012 GMC Sierra 1500 SLE problems after cat back exhaust

[nfolkmann]

I bought a 2012 GMC Sierra 1500 SLE extended cab 5.3L Z71 two months ago. It has under 2000 miles on it yet. I had a local muffler shop put on a cat back system that included a series 40 flow master muffler and dual tips that dump behind the rear wheels. I have seem to notice that I lost low end torque when starting off the line. I do baby the truck and hardly get over 2500 RPMs when accelerating. When going up hills at low rpms the truck will even sometimes shake and does not want to go up the hill. I run only BP premium gas in the truck also. I did also install a K & N air filter in the factory air box. Has anyone heard of any problems with putting aftermarket exhaust on these trucks? I am planning on buying a hypertech max energy tuner in a month for this truck. If I buy this tuner and use the premium gas tune will that help with the problems I am having? Any suggestions will be greatly appreicated it.

[MikeNH]

Not surprised. The pipes are "tuned" to some extent. Run a tailpipe.

 

 

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[Chris]

I lost low end with my flowmaster 40 and it dumps before the axle. ive heard magnaflow is a better muffler as far as not losing as much torque i want to run a pipe out because my drone is bad

[nfolkmann]

MikeNH, when you say to run a tailpipe what do you mean by that? Are you talking about changing the pipes to come out under the bumper? I did find on line a diablo tuning dealer here where i live. I seen they offer custom tunes. I emailed asking them if they had any suggestions with what I have done to truck to get low end back by doing a custom tune. I have already had the truck in the muffler shop twice because they usually use a knock off flow master so I had them put a true flow master on it after we did figure out there was some slight difference to the muffler. I actually called flow master too and they said the 40 series muffler should work fine on the truck and provide enough back pressure to keep low end torque. The low end torque was so bad at one point I was trying to climb a steep hill and I had to manual shift it down to get the RPMs up to get the truck to climb the hill. I know I can prolly fix my problem by having them put the stock muffler back on and keep the tailpipes but I do not like a quiet truck. I have even tried reseting the computer and ran 2 tanks through the truck to see if that would help. It does seem like it has gotten better with a true flowmaster muffler but it is still not back to what it used to be.

[kstruckcountry]

I would guess the problem isn't the muffler, probably the pipes if they custom bent them.

 

A Magnaflow would provide less back pressure than a FM, as it's a straight thru muffler with no baffles. I didn't notice any power loss with mine, but I'm running the factory pipe.

[nfolkmann]

kstruckcountry, so all you did is pretty much cut the factory muffer out and put a new muffler in? Do think on mine there is too much restriction with the custom bent pipes? If I remember right I think outlet pipes on the muffler is 2.5 inch. Would I be better go to a bigger outlet pipes to get it less restriction. They used a ram style bender when bending the pipes not mandrel. If needed I can supply pictures if that helps.

[MikeNH]

Lack of tail pipes will cause a loss of low end and electronic tuning probably won't help. When I say the pipes are tuned, I mean the routing and size used aren't just random, there is testing behind it. I bought a dB (Corsa muffler w/lower grade stainless pipes) exhaust for like $550. Quiet when crusing and a monster when you step on it. Search "Silverado dB exhaust" on YouTube and its one of the first hits. I'd recommend that over a cut and weld job with a flowmasters. I owned one kit from them on my 2003 Silverado and it was junk, never again.

 

 

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[nfolkmann]

Mike NH, from the factory it only had a single pipe. I would definitely want dual outlet pipes. I really do not want to start over on this exhaust system beings I am already $600 into it. Is there anything I can do with the existing exhaust?

[MikeNH]

Run it out the back or learn to live with the power loss at the low end. You can try checking with one of the folks on here from Blackbear or Diablosport but I don't think any kind of tuning will solve what you've experienced but I'm far from an expert with that. In general I'd say people here have reported even running duals out the back to cause some low end loss, I stuck with single outlet because duals don't offer any real gain and straight out the back will just make towing annoying as sound will reflect off an enclosed trailer.

[bossier62guy]

From the sounds of things you had an aftermarket muffler installed along w/ some custom exhaust work. That's not really a cat back system. Pipes dumped over the axle are actually more efficient in helping evacuate exhaust gases versus running them straight out the back. Your pipes are large enough, don't go bigger or you'll really lose low end. Why are you running premium fuel in a truck that hasn't been tuned? Go back to 87 octane and save your money. Was the K&N installed at the exact time the exhause was installed? I'm running an almost identical setup on my truck as you are w/ the exception that I'm using a Magnflow muffler and I didn't experience any issues whatsoever. You might get more responses if you do throw up some pics....

[Doug_Scott]

I am running a magnaflow muffler, with two outlets, and two tailpipes that end behind the rear wheels, out to the side. Did not notice any loss in power when it was done. Mind you, I have the 4.8 with the 4 speed, and at the time 3.23 gears. Could not get much slower.

One thing you may want to consider, the weather. Around here it has been very hot and humid for the last 6 to 8 weeks. This weather just kills the power.

Have you tried using the tow mode? That will hold the truck in gears longer, maybe make a difference for you. And stop with the high octane fuel until your truck has been tuned to take advantage of it. Premium fuel is not better fuel.

[kstruckcountry]

kstruckcountry, so all you did is pretty much cut the factory muffer out and put a new muffler in? Do think on mine there is too much restriction with the custom bent pipes? If I remember right I think outlet pipes on the muffler is 2.5 inch. Would I be better go to a bigger outlet pipes to get it less restriction. They used a ram style bender when bending the pipes not mandrel. If needed I can supply pictures if that helps.

 

 

Yeah I had a 14" Magnaflow, but I swapped it out for a 5x11x22 Mag. It's drone free on the highway, but still rumbles nice when it's loaded up or I want it to.

Going with larger pipe won't help anything, it would probably lower your exhaust velocity and make it worse. Post some pics, let's see what you have...

[nfolkmann]

I agree with all you on the premium gas. I am going to start using road ranger 87 octance. I read online they are a top tier fuel which GM recommends. I figured BP gas would be a top tier but it is not on the K&N was installed before the exhaust. I have tried going back to the oem filter and cleaning the map sensor in case oil built up on the map sensor. One thing I might try is before taking any exhaust parts off I will go to only 87 octane gas and oem filter again and run a tank through and see if it gets better. Yes is has been really hot and humid this summer. I will notice the lunging up a hill though the most when I back it out of the garage in the morning on my way to work and it is generally cooler but could be humid. The tailpipes are custom. This will be the second truck I took to a local shop called professional muffler. They have always done great work for me. I had a 2006 gmc sierra sle with the 5.3 before this and never really had this issue. I understand though the two trucks are quite a bit different. Attached are some pics of the exhaust.

 

 

 

 

 

 

 

 

 

[nfolkmann]

Also if magnaflow is the way to go. I know I can alway buy one and take it to the muffler shop and they will put it in for me for cheap. I am willing to spend another $100. I just do not want to have to start over and put a whole new exhaust set up on it. I would like some guidance on what magnaflow muffler to put on as far as size and tone.

[bossier62guy]

I wouldn't say Magnaflow is the answer....plenty of folks here are running Flow Master mufflers and love them. As far as the K&N is concerned I've been running one on my 5.3 for about 80K miles w/ no problems whatsoever. Switch back to 87 octane and give that a shot. Your exhaust looks fine to me.