Couple of mods.....now no power

[73shark]

The stock exhaust is 2 7/8". Not sure another 1/8" would make the vehicle not move w/o 3/4 throttle.

Too little back pressure can affect the torque curve but still it sounds like there's more happening here than that.

I had the factory catback on my 2007 and even tho it had a straight thru muffler, there was no change in low speed throttle response.

 

[Zed 71]

IMO 3-inch diameter piping is too large for the 5.3L. Yes it does not sound like much of any increase, but the frictional losses are exponential regarding changes in diameter. The flow is now turbulent (versus laminar) and now the exhaust velocity decreases which reduces exhaust scavenging. A tune would definitely help to reduce this and address the annoying 6-speed.

In my opinion better to stick with stock piping diameter and just change the muffler then tune. Hopefully one of the tuners will chime in. If you get the EFI tuner you can change back to stock when you visit the dealer.

 

[MudnRox]

IMO 3-inch diameter piping is too large for the 5.3L. Yes it does not sound like much of any increase, but the frictional losses are exponential regarding changes in diameter. The flow is now turbulent (versus laminar) and now the exhaust velocity decreases which reduces exhaust scavenging. A tune would definitely help to reduce this and address the annoying 6-speed.

In my opinion better to stick with stock piping diameter and just change the muffler then tune. Hopefully one of the tuners will chime in. If you get the EFI tuner you can change back to stock when you visit the dealer.

Ok just a question here as I'm trying to learn. If the tube diameter is too large for the engine, then why would Magnaflow make and market the product?? As I stated before I had the same kit, as well as a CAI, on a 2009 Tahoe 5.3L and had no problems.

I have talked with Magnaflow about the problem. They have never had any complaints about this kind of situations with this vehicle. I even asked if there was a kit more suited for the engine and vehicle. They assured me I had the right kit for the application. But they were very helpful in trying to determine the problem. Of coarse they say its not related to exhaust. I also double checked to make sure their muffler was non-directional(thinking maybe it was installed backwards).

I have a dyno-tune scheduled for next Tuesday at a very reputable local shop. I stopped by there today and talked with him for quite a while. He's certain he can resolve the issue. The vehicle will be checked bumper to bumper and by diagnostic computers before any tuning is started. I will keep you all posted.

Thanks for the advise, opinions and help as I'm trying to sort thru this mess. I learn something new every time I get on the site.

 

[TheFuzz]

Good luck man. I'm interested to see if this really is just a tuning issue or if there is something more going on. Every vehicle is different. Some are built on the looser end of tolerance, some tighter. Maybe your motor is too close to either end of the spectrum and tolerance stacking between the motor and the exhaust is causing some kind of issue. Who knows.

 

[JennaBear]

Have you checked your intake tube? Maybe it is loose, common issue. Doesn't sound like something a tune will fix.

Sent from a jelly bean.

 

[MudnRox]

Have you checked your intake tube? Maybe it is loose, common issue. Doesn't sound like something a tune will fix.

Sent from a jelly bean.

Yes I have checked it.

 

[cjweb11]

I'm no expert, but is it really possible for a properly installed intake tube and 3" catback to have this effect?
I ask bc I have the Airaid Jr tube/dry filter and a 3" catback without any tuning (yet) and i feel response is slightly better if anything, while mpg has dropped just a little.
If Jenna has her doubts about a tune being the answer then I certainly have my doubts too

 

[doubletapdrew]

Breather hose still attached to valve cover and Airaid Jr?

 

[tights24]

Yeah, I agree with a lot of the other comments. I don't see exhaust and CAI causing a problem like you're describing. These are very common items that millions of folks have installed on their vehicles with no serious adverse side affects. Of course this is just my opinion once again, but I think minimal changes like what you have done do not need a tune to make right. Especially as drastic as you mention.

I'm not up on the exhaust system on these trucks but is it an easy bolt on system from the cats back? If so, it may be worth putting your old exhaust back on to see if it makes a difference. Same with the CAI. See if you can narrow it down.

Some questions I have:

1. Is your MAF clean and/or did you bump it by chance or leave it unplugged?
2. Did you check the inside of the catback tubing AND muffler for packing material? on a previous vehicle Magnaflow saw fit to have the muffler stuffed with packing material........
Good luck.

 

[MudnRox]

Breather hose still attached to valve cover and Airaid Jr?

Yes it is.

---------- Post added at 07:02 PM ---------- Previous post was at 06:48 PM ----------

Yeah, I agree with a lot of the other comments. I don't see exhaust and CAI causing a problem like you're describing. These are very common items that millions of folks have installed on their vehicles with no serious adverse side affects. Of course this is just my opinion once again, but I think minimal changes like what you have done do not need a tune to make right. Especially as drastic as you mention.

I'm not up on the exhaust system on these trucks but is it an easy bolt on system from the cats back? If so, it may be worth putting your old exhaust back on to see if it makes a difference. Same with the CAI. See if you can narrow it down.

Some questions I have:

1. Is your MAF clean and/or did you bump it by chance or leave it unplugged?
2. Did you check the inside of the catback tubing AND muffler for packing material? on a previous vehicle Magnaflow saw fit to have the muffler stuffed with packing material........
Good luck.

1) I'm guessing the MAF is clean, but I did not clean it as the vehicle had about 4K on it when it was installed. I got the Airaid JR with the dry filter, but I'm still running the factory filter. And yes the MAF is plugged in. Not sure if it was bumped at any time but it sure wasn't knocked around.

2) I personally did not install the exhaust. It was done at a buddys shop in exchange for some adult beverages. I would like to think that he checked it. But I will double check myself first chance I get. That is honestly something I had not thought about. Thanks for bringing that up. I did consider the possibility of the muffler being directional and I did check for that.