JorgeRod54

I threw two high flow cats on my truck about a year ago with my new exhaust system. magnaflow 94136. ive noticed that the truck seems to lag a bit, even with my custom tunes. After my engine was replaced (whole different story) a couple of weeks ago, I noticed that my truck ran a bit sluggish, even with a new engine and my tuner enabled. still only getting about 11mpg, which, personally, i think is still a little low, even with a new engine. My buddy who runs a truck shop here in san antonio looked at the high flow cats and is saying i might have lost backpressure because of the straight flow-thru cats, since they're meant for high horsepower engines,and is suggesting I go with regular cats.

That being said, has anyone used the 94136 and noticed any power loss or loss in fuel mileage? I know its a truck, and trucks are gonna be rough on gas, but the lag is what bothers me too.

Thanks guys!

Especial86

iTrader: (1)

Elaborate some more on this "lag".

Is it stumbling off the line?
Feeling like the brakes are dragging?
Feel like a transmission slipping?

I wouldn't suspect a lack of back pressure issue or a bad cat, unless you had some misfires dumping raw gas into those cats before you swapped motors.

JorgeRod54

That was the reason I replaced the stocj ones in the first place. The truck just feels like it's being starved of something. Idk if it's air or fuel. So it just feels Lk it has to struggle to pick up speed. I'll hear and feel the engine change it's tone, like a sensor registers something new. Just had the brakes serviced, so theres no drag

JorgeRod54

When you put the pedal down, you want the truck to get moving in traffic, not just downshift, make a lot of noise, and struggle to pick up speed

Especial86

iTrader: (1)

Did it ever run strong with the new engine?

I'm wondering if the problem is with your intake manifold..

JorgeRod54

It's got times it does and times it doesn't. Colder days it does. Makes me wonder if it has to do something with my intake or the MAF. There's a lot of process of eliminating I have to do for air/fuel

Especial86

iTrader: (1)

If if runs good on colder days when the air is denser then yeah, I'd be looking at intake troubles too.. Are you running a CAI or stock intake?
The foam on the stock unit is well known to cause a bog/moan when its deteriorated.

JorgeRod54

K&n fip kit I installed back in 2007. Got a custom tune from php to compensate for that

Especial86

iTrader: (1)

Check your fuel rail pressure on your tuner.. Let us know what you come up with

Has the FPDM been changed out yet?

I'd still be considering an air issue over a fuel issue, so VAC lines, throttle body, intake manifold, and all subsequent connectors and connections are worth an inspection.. You can spray a bit of WD40 around these areas just to see if the rev's jump or climb a bit.. But I really think your issue might end up being something stupid and easy to fix.. Something may not be completely connected or disconnected after the motor swap.
If the motor runs strong otherwise, and only bogs or lags under a load while driving it could possibly be your TPS sensor on your throttle body, or the throttle body itself.

JorgeRod54

Throttle body has been replaced, FPDM in in the glove compartment to change when I get my tools up here, most connections look well. I clean the throttle body and connections regularly with tb cleaner and electrical cleaner and maf sensor cleaner. I'm more than sure it's a stupid problem. I know the guy who put my exhaust on was a meth head and did the entire thing for 400 bucks, so idk if the tick, which I'm more than sure is a damaged cat, might be the bigger issue of it all