Lately I've been only getting around 11-12 mpg on city/freeway driving in the car in sig. Anyone know what the problem could be?

P.S.--I have a brand new Fuel Pump and Filter.

 

How long has it been since the car's had a good tune-up (spark plugs, spark plug wires, distributor cap and rotor, PCV valve, air filter, etc.)? Have you checked for codes or is the SES light ever on? Does the car seem to run fine, is there any hesitation, running rough, etc.? Checked for vacuum leaks?

It could be any number of things, need more details.

 

Good tune will make the world of difference.

Bill

 

Could be the engine thinks it's in constant warmup mode .. therefor it pumps more and more gas into the engine for no reason

(I myself may have a little bit of that due to me dropping in a 160 thermostat with holes drilled in it ... bad idea o nthe freeway)

How's the rpm .. does it idle ok .. or a bit high ?

Check the IAC ... hmmm the CTS may be faulty too


What kind of O2 sensor do you have ? Some of them I heard cause the engine to run a bit rich

 

It's probably due for plugs and wires, but it still runs strong and idles fine around 800 rpm no hesitation. The SES light does come on occasionally on and off, no vaccum leaks, and the O2 is a regular stock replacement.

 

Check for engine codes

O2 sensor .. stock yes but.. is it a Bosch ?

 

New fuel pump ??


Did this happen shortly after installing a new fuel pump ?

 

Dude if it was wires you would know. Like the engine would probably miss because of a burned up spot on the wire. I once had 3 bad wires before changing it. My gas mileage was so ****ty. Like my tank was gone in a hundred miles because it was missing so bad.

Bill

 

I don't know how long after but yeah it started sometime after the new pump/filter.


--My tanks only lasting 115-120 miles tops, WTF?

 

I recommend a stock 195° thermostat and the stock aircleaner with the preheat and thermvac switch operational.

Then clear the codes. If the SES comes on again read codes and go from there.

What fuel pump did you use? Hopefully not something that flows too much, otherwise the stock regulator won't be able to regulate the fuel pressure down to stock pressures.

RBob.

 

It's just a stock OEM fuel pump and filter, don't know what brand.

It's still getting 10.5-11 mpg city driving, and I don't know why!---It still runs good though.

 

Just outta curiosity ... your open element conversion .. how did you do it .. exactly .... meaning do you still have all the original wires hooked up ? i.e. air temp etc

What brand is the pump ?

Fuel lines twisted or not ?

 

The open element is not the prob. I've had it for a long time and this mpg prob. is recent.

Don't know what brand exactly my mechanic used but, most likely it's bosch.

Fuel lines are not twisted.

 

I switched to MSD 8.5 mm Super Conductor wires and saw a 2.5-3 MPG gain. This is after just replacing the wires with Accel 9000 series wires with heat guard boots. I melted one of the wires and just replaced them all. The 50 ohms per foot resistance in the wires caused my mileage gain. Stock and the Accel's were 1200-1500 ohms. Try it you won't be disappointed and if you later decide to go with a 6AL ignition box, the wires are up to it. Huge improvements at 3300 RPM and above with the box.

Make sure your fuel filter was put on in the right flowing direction.