I have a 99 silverado 5.3.
Performabuilt with 1200 flash stall
Latest factory tune
Custom CAI.
This is my daily driver and may eventually do more, but I'm wondering what happened to the mileage. I was getting around 18 mpg and now I can't get more than 15. I know it will use more fuel than the factory set up, but I didn't think that with the trans and CAI it would drop it that much. It isn't kicking any codes either. Any help is greatly appreciated.

 

i took a hit on MPG with my performabuilt trans and a 300 stall . I just installed a finish line level 7 and a circle d converter and immediately saw a difference in MPG. Im thinking it might have been the converter

 

The stall is what is hurting your mpg. I was getting around 18 mpg with longtubes, 430 gears and stock converter, on stock 20 with 275/55s and a custome tune. I lost about 3 mpg when I put the 3000 stall in and then lost about 1 mpg from the 220 cam. On average I get about 14mpg now, not too bad for a heavy crew cab with gears, cam and stall. Ok can also get about 5 mpg if I stay in the throttle!

 

Thanks for the time. I wanted to make sure there wasn't something I was missing. Because my converter stays locked most of the time driving.

 

If your CAI has a big open element air cleaner under the hood then it is really a HAI hurting performance and mileage.

 

So you're saying that higher intake temps are to blame?

 

The warmer the air is, the more efficent the motor is. For fuel mileage that is, thats why you don't get the same gas mileage when it -10º outside comapred to 75º.

And there is likely maybe a 5 hp difference if that if you compared a HAI and CAI in real world conditions, it just doesnt matter that much.

 

dam thats still good i get 9 mpg or less on my cammed 6.0 2 door tahoe it sucks i hate it ....and yea could be your converter

 

Baloney. Hot air is less dense and makes less power. The pcm calibration pulls timing out of the tune as IATs go up. I see IATs of 160-190 degrees here in Okla on trucks with supposed CAIs with open element air cleaners. There was a K&N open element kit on my 04 when I bought it. I have data logs of my truck idling in traffic with IATs over 190 degrees. I took that crap off and gave it away. I'm now running a stock airbox with an Airaid tube. I love hooking up my scanner and showing people what their IATs are with their supposed CAIs.

 

Not trying to start a thread war,

But this is correct. In the IAT spark table, there are modifiers to pull timing if the IAT temp is X degrees. On the Gen3 motors, I think it can pull upwards of 10-degrees of timing at times.