Hey guys well my vert is running pretty rich. The gas fumes are pretty strong, I get horrible gas mileage, a full tank gets me maybe 150 miles. I'm running a gutted cat with no split pipe cause I couldn't seem to find where the other end goes. I was thinking its probably the o2 sensor because with or without it plugged in, it seems to run the same, but it only has about 2000 miles on it. Any suggestions?

 

Bump

 

Check the injectors, replace the cat and connect the airpipe.

 

Having no cat would effect my mpg?

 

having no cat, resonators, hopefully it still has all the emssions ( i live in cali so its hard to get away with not having them) and injectors.

 

Just because I don't feel like making a new thread. Does anyone know the best place to buy a new o2 sensor. And would doing a cat delete really help with gas mileage? I'd like to atleast replace the pre-cat. Does anyone know which headers will delete the precat or both cats?

 

Ebay for a new 02 sensor. Get the Bosch sensor with the green clip. Plug and play. A working one will increase the MPG by as much as 50%! Yes 50% if your current 02 sensor is broke.

Cat delete will drop weight, reduce backpressure, and increase power. This will increase gas mileage with all other things constant. You would have to do a controlled test to tell the difference but it is there. More important would be a tune up and tuning the fuel via a SAFC. FC's run pig rich stock. Also getting a cheap narrow band A/F ratio gauge and learning how to read it will increase your MPG greatly. It will tell you when you are in closed loop mode and therefore you will learn how to keep it there. It will also show you when the injectors are cutting out on deceleration with the car in gear above 1500rpms. This is a OEM feature in the ECU to save you fuel.

Any header will delete the precat. A "presilener" from RB or similar replaces the main cat. You can also get the Rotary Performance precat delete cheaper to remove the precat. that once keeps the cast iron collector bolted to the block.

 

Gutted cat and split air pipe not hooked up will not affect MPG.

Do a full tune up first (fuel filter, spark plugs, air cleaner, ect). If no change I would suggest getting a cheap (autometer) narrow band A/F ratio gauge. As well as what I posted right above about the A/F gauge it will tell you if your 02 sensor is dead or not.

 

This might be a stupid question, but it's a common cause for issues like this:

Are you running a Fuel Cut Defensor? Take that off and see what happens.

 

I have an S5 and I have never seen a plug and play o2 sensor for an S5. This all sounds like it'll get very expensive which completely destroys the point of saving money via fuel cost. If there is one thing I know nothing about it's tuning and A/F ratio's. Not only do I live 7+ hours from the nearest tuner but I only make a small amount of money.

 

You can actually tune and NA rotary to an extent on the street. The idea is you are backing off fuel somewhat, not tuing for max power. Do some poking around with the search feature here and you may find that it is easier than it sounds. Used SAFC's can be had for little more than $100.

Also, saving fuel is only part of the benifit. Running rich hurts more than just fuel economy.