hey guys, does anyone have any ideas why my 94 3.4 is getting bad mpg, i mean it used to be alot better, its not "horrible" but worse indeed, plugs and wires are old (not sure how old), maybe o2 sensors, bad cat ? i have a k&n CAI on it so its getting air, i usually run 89 octane (plus) not regular any ideas guys ?thanks !

oh ya, i usually shift at 2500-3000 rpm

 

got to do the wires and fuel filter.... stuff like that.

 

bad fuel filter maybe . It could be oil. I have heard that if u use the wrong oil it will give bad gas mileage.

 

If the truble lite is lit, take care of that problem first. Then start by giving the car a tune up, plugs, wires, clean air filter. Get a scanner and check the operation of the O2 sensor. Check fuel pressure & pressure regulator, check back pressure to see if cat & exhaust sytemare clear. make sure brakes are not dragging & tire pressure is OK. Make sure TCC is working properly.

 

alright man but ive never checked an o2 sensor, or back pressure before how do i do that ?, and where is the fuel pressure regulator located on the 3.4's?

 

The O2 sensor is tested with a scanner. It should show a continuously varying voltage centered at about 500 MV. If the voltage is not changing or only changing occasionally, the sensor is bad and should be replaced. Back pressure is tested by removing the O2 sensor and screwing in a pressure adapter in its place. It should be less than 5 PSI at idle. The fuel pressure and regulator are tested by attaching a FI pressure gage to the test valve on the fuel rail. Use the same procedure as in the sticky for the LT1 engine.