i Have a true dual exuast with glasspack mufflers. Since it has no backpressure does the system run rich. IM getting 4mpg and im going back to a stock exhaust. I was just wondering if that was the reason for running so rich. I have a new precat sensor on it.

 

i don't think lack of backpressure would have any effect on mpg, and i've never heard of anyone getting that poor of mileage, even with dual 4 barrels.

where is your precat sensor in this true dual setup?
and do you have any CEL codes ?

 

the sensor is about where it wld be if there was a cat on it. There is a cel but it is for the upstream o2 sensor.

 

How big are the pipes? with true dual you should have about 2" pipes. The upstream o2 sensor controls the A/F ratio and is more than likely the cause of your rich running.

 

2.5" pipes mufflers are 2.25 ya i know its to big but i didnt think it would hurt that much. How does this make the cel go off for the 02 sensor?

 

You need to check the voltage on the upstream o2 sensor since it is new, you may have gotten a dud.

 

do i check where it plugs in? so it doesnt hav anything to do with back pressure? a mechanic said since i dnt hav a cat the lack of backpressure cuases it to run rich

 

my opinion is that neither backpressure nor pipe size is causing your excessively low mpg problem.

you do know that pre-cat 02 sensor and upstream 02 sensor is the same thing right ?
and that it monitors the exhaust and sends a signal to the pcm, which controls the fuel mix, right ?
and that the post-cat 02 sensor and the downstream 02 sensor is the same thing, and its only job is to monitor the exhaust after the cat, so the pcm knows the cat is reducing emissions. it doesn't directly affect the fuel mix, but its part of the whole sensor communication process.

and you didn't answer my question - where in the scheme of your true duals is you pre-cat 02 ? is it in an H-pipe, or an X-pipe, or is it in only one side of the true duals ? you've got to explain your setup if you want help.

what is your CEL code. give me a number.

 

Ok your gonna have back pressure with that setup, and its not the cause of your poor mileage, your pre-cat/upstream 02 sensor can very easily cause the bad gas mileage coupled with a bad plenum(probrably the reason the 02 sensor went bad) I could easily see that bad of mileage. plus I noticed you have 35s and no mention of gears.

When was the last time you did a tuneup?

x2 on the CEL code number

 

the sensor is only on one side. yes i know there the same thing. I recently did a plenum gasket, rotor and cap,and plugs. I havent changed the gears but on the highway i used to get 12 mpg with the tires.

Im going to have to get the code nmbr later becuase a mechanic did it.