I don't know what happened. Maybe it was floridas hot muggy air, or maybe my fuel filter, or maybe a tune is needed... Again. Has anyone lost about 2 mpg randomly? How did you fix it? I know I need to change out my fuel filter. Could that be it? Also when when my car idles it smells very rich. Also my tail pipes are turning black.

 

Losing Two MPG loss does not happen over night, that's approx 10% loss of fuel economy... If you haven't already.. Scan the PCM for DTCs, Do a quick burst down the highway at WOT , if it's a fuel restriction you will notice a lack of power... Though having black smoke and a rich smelling exhaust kind of contradicts a lack of fuel concern. Start with the simple things.. Pull your air filter out and inspect the housing for restriction, fuel system leaks.. Vacuum lines integrity... There could be a numerous amounts of sensors and inputs that can contribute to poor fuel economy.. Ex.-O2 sensor, MAF,ECT, Injectors, A scan and visual inspection is the first critical step. Then we can take it from there. Good Luck!

 

i ended up blowing my cats out into my mufflers, so i had to hollow out the cats... i have not been tuned since i blew the cats. ive had O2 problems forever. i changed out the sensors and pigtails because it was a shoddy splice job due to LTs, but now... it could be multiple things... i still get the CEL on a daily basis but i figured it wasnt a big deal because of the O2s.

 

So what DTC's are you getting ?

 

Rear o2s are not a deal. Front o2s are a big deal

 

I think they are p133 and p153. They are my O2s on my header collectors (front)

 

P0133-Bank one sensor one slow responding
P0135- Bank one sensor one ckt fault-heater

As mentioned above the bank one and two sensor one... (upstream) sensor are critical for your fuel economy and performance... If they are not able to properly calculate the efficiency of the engine , fuel economy/performance will suffer.

 

Maaaaaaaaan, I replaced those and the pig tails awhile back...

 

This will help you understand why it's vital...

An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gasses leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts. The sensor does not begin to generate it's full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor *will not spend any time at 0.45 volts*. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an "illegal" value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution. The O2 sensor is constantly in a state of transition between high and low voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison is not possible.

 

Running long tubes? You need a custom tune for the long tubes do to the fact the are further away from the engine and will respond differently

 

I've had my car Dyno tuned a few times already. Only thing that changed since my last tune was hollow cats.

 

Did he account for the long tubes for shure?

 

I don't see why not. It was a very reputable speed shop in Virginia. They did a lot of mustangs and track cars.

 

Might just need new o2 sensors then.
The slow to respond codes and slow to heat usually mean the o2s were not programmed correctly

 

Even worse now. 13mpg. I ordered a tune from Steeda. They said they should be able to fix it.

 

Well got the tune. Now we play the waiting game for results.