Well ever since I got my headers and 3" exhaust installed, the car seems to be consuming gas a bit faster than before. She was never really that good on gas, but now especially it is getting frustrating with gas at 2.99 a gallon. Has anyone experienced this before? I guess I will have to have a custom chip burnt too really get it where I want it. But other than SLP runners and K&N's, the motor is all stock.

Will

 

That doesn't sound right. Headers and full exhaust should usually give an increase in mileage.

 

You dont need a custom chip yet and as said above. MPG should be up with a free flowig exhaust and intake. I was getting 26MPG with my 350 TF Heads and LT4 cam with the superram. And I was still on the stock chip.

 

defective cat then? The entire system is new. I only replace it and slp runners. but the car feels like it has less power and it's going through gas more quickly. the o2 sensor is new as well. I don't know why it would be doing this. I figured the same thing,that I would see a slight increase if not the same mileage. Any ideas where to start? I am trying to get my hands on an aldl cable so I can take a look at things

Will

 

Most of the time after a header / catback install when you lose gas mileage it's YOU that is doing it, but not realizing it. You probably play around a little bit more than you normally do on the street. You have to realize that it's much easier to consume more gas with more mods. But in the other hand it can give you much better gas mileage if you granny it all the time.



My suggestion, granny the car (slowly get up to speed, stay at speed limit, dont try passing anyone, basically dont go over 2500, and dont get to 2500 in a hurry) and see your gas mileage then.

 

Not likely, but you did have your spark plug wires wrong and were dumping raw fuel into the cat and the casing was glowing red/orange from the ignition of fuel in the cat. That is one way the cat gets destroyed.

So the cat may have been functional, and now is molten and deformed. If you can, pull the cat and take a look. You should be able to see clean through a new high-flow cat. The honeycomb should be cleanly formed.

 

replace your O2 sensor when you install headers. The corrosion resisting paint they spray on the headers usually damages O2 sensors.


edit: nevermind you have Jet-Hot
replace the O2 sensor anyway.

 

When you add an aftermarket exhaust on these cars you are increasing the volumetric efficiency of the motor by up to 10% (that is on TBI cars when going from 2.25" to 3" pipe). The parameters in the chip are set for the VE that the motor has when stock. Your motor is now slightly out of tune. To get back the MPG you will need some chip work. You still have increased the power level of your motor but like any FI car you need chip work to make it perfect. I saw an increase in my MPG when I added a cat-back. Doing so decreqsed some of the pumping losses of my car all while not changing the VE that much. When I added headers my MPG went way down. Chip work will bring it right back where it was when it was stock.

 

I put in a brand new o2 when I installed the headers, but thanks guys, you've all been most helpful. I will work on getting that aldl together as well as some chip burning equipment. I am eager to start learning about tuning. In the mean time I will try to adjust my right foot as much as possible and see if I can't get it to run a few more mpg.

Will