careldo Posted January 23, 2004 Report Share Posted January 23, 2004 i am wondering if anyone can shed some light hear on why my mpg was been decreasing for the last month. i have changed my plugs,wires,cap rotor, checked fpr and timing all ok and all parts oem.I am stumped and not sure where else to look. btw:i always use premium gas and also have checked the brakes for binding. Chris Link to comment Share on other sites More sharing options...
Bruce Nunnally Posted January 23, 2004 Report Share Posted January 23, 2004 Cold weather causes decreased tire pressure, so you should check the air pressure in your tires. The gas forulations change in some areas from summer to winter. This can cause some variance in mpg. It is very difficult to measure exact mpg changes without careful controls. Bruce 2023 Cadillac CT4-V Blackwing Follow me on: Twitter Instagram Youtube Link to comment Share on other sites More sharing options...
Dloch Posted January 23, 2004 Report Share Posted January 23, 2004 Obviously temperature in the area you live in has a big impact on your fule usage. I'm in Michigan which is very cold right now, at the beginning of last week Monday I drove the car down to Cincinnati. Left at O dark thirty, was cold but not near as bad as it right now. In any event the car was full of fuel, I believe I drove about 100 - 110 miles before the needle moved off full mark. This week I was full of fuel on Monday, I didn't get 50 miles and the gauge was already moving down. As of today I believe I have only put about 140 miles on this tank of fuel and I'm not much above 1/2 tank. Simply put the temperature and the distance you drive will have a big impact on your fuel usage, not to mention the fuel blending in your area. The PCM reads the inlet air temp and the coolant temp and continues to add fuel until the temp stabilizes. So if you are only driving a short distance and it's very cold out you're fuel usage will probably double. Dennis Dennis Link to comment Share on other sites More sharing options...
careldo Posted January 23, 2004 Author Report Share Posted January 23, 2004 MAYBE I WASN'T TO CLEAR BUT I HAVE DROPPED TO 12 MPG FROM 19-20 MPG IN SEPTEMBER .I DRIVE 90% ON HIGHWAY I THINK MY MPG'S IS PATHETIC.TRUE IT IS COLD IN MY PARTS BUT THIS HAS BEEN GOING ON SINCE SEPTEMBER WHICH BY THE WAY FORGOT TO MENTION IN MY PREVIOUS POST BUT NONETHELESS I AM STILL SEEING A SLOW AND STEADY DECREASE.I HAVE ALSO CHECKED FOR CODES AND NONE SO FAR I WONDER IF MY OXYGEN SENSOR ARE FAILING AND NOT SET THE CODES. CHRIS Link to comment Share on other sites More sharing options...
Bruce Nunnally Posted January 23, 2004 Report Share Posted January 23, 2004 Clogged catalytic converter maybe? Or leaking injector I suppose but usually that will give other symptoms as well. Bruce 2023 Cadillac CT4-V Blackwing Follow me on: Twitter Instagram Youtube Link to comment Share on other sites More sharing options...
gc_caddy Posted January 23, 2004 Report Share Posted January 23, 2004 Have you checked to see if your parking brakes or calipers are sticking? Cold weather is conducive to sticking and sluggish brake release. Touch your wheels after a run, to see if one or more wheel is hotter than the others. Link to comment Share on other sites More sharing options...
Dloch Posted January 23, 2004 Report Share Posted January 23, 2004 Or leaking injector I suppose but usually that will give other symptoms as well. Or a leaking fuel line................. Where is the FPR on that engine??? Too make that dramatic of a change the fuel has to be going some place. Take the oil dipstick out smell it to see if you can smell gasoline in the oil. I know this may sound dumb but if the motor is running extremely rich it will wash the oil off the cylinder walls and get into the oil, a very thin layer of oil on the cylinder walls helps the rings to seal. Dennis Dennis Link to comment Share on other sites More sharing options...
Dloch Posted January 23, 2004 Report Share Posted January 23, 2004 Have you checked to see if your parking brakes or calipers are sticking? Cold weather is conducive to sticking and sluggish brake release. Touch your wheels after a run, to see if one or more wheel is hotter than the others. Sorry gc_caddy I didn't see your reply before I answered. A hanging brake will certainly cause the same thing................. Didn't even think about that........ Duh Dennis Link to comment Share on other sites More sharing options...
94Eldo Posted January 24, 2004 Report Share Posted January 24, 2004 Had the same thing happen,went from avg 20.5 to 19.5 in a matter of weeks then the shift selonoids went,Replaced them and the MPG's are moving back up. Link to comment Share on other sites More sharing options...
Bob D Posted January 24, 2004 Report Share Posted January 24, 2004 Clogged catalytic converter maybe? As Bruce suggested, I have seen a baffle in a CAT suddenly come loose and resrict flow. The result was a sudden drop in MPG. In a V8 with lots of torque it's sometimes hard to discern this change, and that can also depend on the drivers style. In an older old CAT, (is it?) it may be worth looking into. '93 STS.. opened, dropped, wide...fast. Link to comment Share on other sites More sharing options...
DFBonnett Posted January 24, 2004 Report Share Posted January 24, 2004 Same thing happened to me last summer. Relatively new dist cap went bad. Replaced cap and rotor. Problem solved. YMMV DFB Link to comment Share on other sites More sharing options...
therek Posted January 24, 2004 Report Share Posted January 24, 2004 do you have a remote starter on the car? Link to comment Share on other sites More sharing options...
Ranger Posted January 26, 2004 Report Share Posted January 26, 2004 Temperature will affect MPG somewhat but I have never found more than about 2 MPG differance between summer and winter. I just made a 640 mile round trip to northern Wisconsin to go snowmobiling and it was well below zero. I only averaged 21.1 on the way up but was fighting a headwind all the way. Average for the whole trip was 23.5. If your MPG has dropped that as much as you say I would check the FPR. Link to comment Share on other sites More sharing options...
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