KenD Posted May 7, 2004 Report Share Posted May 7, 2004 I've been noticing a decrease in my mileage over the past year. I used to be getting a good 17-19 mpg in the city but now it's gone down to almost 13-15 mpg. I've lost about 1-2 mpg on the highway also. The car is getting up to 100k soon as it has 95k on it right now. Would new plugs or wires help? Or even a new filter? If there is anything that anyone has done where they've cleaned or changed something under the hood that has resulted in better mileage, let me know. The price of premium keeps going up and if I can squeeze a little more out of each tank, it would be well worth it. Cheers. Ken 1994 STS Pearl White 260,000 KM (163,000 miles) <img src="http://img45.photobucket.com/albums/v137/caesar/caddycaesar.jpg" border="0" class="linked-sig-image" /> Link to comment Share on other sites More sharing options...
JasonA Posted May 7, 2004 Report Share Posted May 7, 2004 Start with the common-sense items. Check the condition of the spark plugs and wires. After close to 100,000 miles and 10 years, I would suspect these items may be in need of replacement. This isn't always the case, but if you're noticing a dramatic change in your fuel economy, that may be part of the cause. Put in a new air filter and change the fuel filter. Change the PCV valve also. Check the air pressure in your tires. I run mine at 35 psi or more. Lower rolling resistance equals better fuel economy. Also, check your converter for signs of pluggage. If you tap it with a rubber mallet, does it rattle? The converter may be plugged or clogged. Also -- try a few tanks of mid-grade (or even regular). Premium is the recommended fuel for best performance under all conditions, but you may be able to run a lower grade of fuel in your car. Run 87 or 89 for a few tanks and listen for spark knock, especially under heavy throttle. If you don't hear any, that means the spark control system is operating correctly and correcting the spark timing to compensate for the lower octane gasoline. You may or may not get better mileage out of lower octane gasoline, but you'll certainly pay less at the pump each time. Good luck, Jason(2001 STS, White Diamond) "When you turn your car on...does it return the favor?" Link to comment Share on other sites More sharing options...
Rich W Posted May 7, 2004 Report Share Posted May 7, 2004 Have they changed the gasoline formula in your area? I'm getting 1-2 mpg less than I did over the last few years, but if I take a trip to central or southern Illinois, where the gas formulation is different, my mileage goes up as much as 2-3 mpg. I know we have up to 10% ethanol in the metropolitan areas, but I sometimes think they are adding more or changing the formulation to reduce mileage. Taxes are paid per gallon, so if we average less mpg per tankful, we have to buy more gas, thus paying more in tax. It's an easy way of raising the tax on gasoline without having to tell the driving public that you want to raise gas taxes. Just my two cents. Link to comment Share on other sites More sharing options...
KenD Posted May 7, 2004 Author Report Share Posted May 7, 2004 Rich, last summer when I drove out to the cabin I was using about 9.5-9.9 litres of gas for every 100 kilometres. I believe that this works out to about 25+ mpg. Shell Petroleum was having a promotion on their new formula of premium gas when I was getting that great hwy mileage. Now I'm lucky if I can get 11.0 litres per 100kms with the same gas. Who knows, they suck you in. How are we to tell how great the gas really is? Ya know what I mean? 1994 STS Pearl White 260,000 KM (163,000 miles) <img src="http://img45.photobucket.com/albums/v137/caesar/caddycaesar.jpg" border="0" class="linked-sig-image" /> Link to comment Share on other sites More sharing options...
Marika Posted May 7, 2004 Report Share Posted May 7, 2004 Rich, last summer when I drove out to the cabin I was using about 9.5-9.9 litres of gas for every 100 kilometres. I believe that this works out to about 25+ mpg. Shell Petroleum was having a promotion on their new formula of premium gas when I was getting that great hwy mileage. Now I'm lucky if I can get 11.0 litres per 100kms with the same gas. Who knows, they suck you in. How are we to tell how great the gas really is? Ya know what I mean? I agree, I believe the oil companies have changed the formulation of the fuel so it gets used up faster, you get fewer miles to the gallon, while at the same time, raising the prices. I too have noticed much lower gas mileage and yet my car runs well and recently passed inspection including a very strict pollution inspection. I've also noticed many more car fires and I'm starting to suspect that whatever the formulation, it's directly responsible for these fires by damaging the fueling systems in cars. If you really want to make people safe drivers again then simply remove all the safety features from cars. No more seat belts, ABS brakes, traction control, air bags or stability control. No more anything. You'll see how quickly people will slow down and once again learn to drive like "normal" humans. Link to comment Share on other sites More sharing options...
tjtjwdad Posted May 8, 2004 Report Share Posted May 8, 2004 This may sound off the cuff, but check your gas cap. If it's worn it can cause fuel consumption to increase. Jim White Link to comment Share on other sites More sharing options...
Ranger Posted May 8, 2004 Report Share Posted May 8, 2004 I think Al-Queda is behind it. Link to comment Share on other sites More sharing options...
JimJ Posted May 8, 2004 Report Share Posted May 8, 2004 If there is anything that anyone has done where they've cleaned or changed something under the hood that has resulted in better mileage, let me know. The price of premium keeps going up and if I can squeeze a little more out of each tank, it would be well worth it. Cheers. Ken Drive slower, 5 KPH slower will give you 1-2 more MPG. I tried driving with my cruse set at 60 MPH. I slow to 60 on the up hills. I hold the throttle open a little on the down hills and let it pick up speed. doing this I can get 28 MPG. Link to comment Share on other sites More sharing options...
Marika Posted May 8, 2004 Report Share Posted May 8, 2004 I think Al-Queda is behind it. If you really want to make people safe drivers again then simply remove all the safety features from cars. No more seat belts, ABS brakes, traction control, air bags or stability control. No more anything. You'll see how quickly people will slow down and once again learn to drive like "normal" humans. Link to comment Share on other sites More sharing options...
Rich W Posted May 8, 2004 Report Share Posted May 8, 2004 Larry, sorry to sound conspiritorial, but...... It isn't Al-Queda. It's something worse..... the U.S. Government. My wife and I started mixing 89 0ctane mid-grade with premium in our CTS and have had great results. We actually picked up about 1 mpg in suburban driving. I still can't keep my foot off the accelerator when some clown in a BMW or some ricer comes along side at a stop light, but I have tried to drive more reasonably. The STS is just down on mileage. Guess I'll have to try mixing fuels on that car. Link to comment Share on other sites More sharing options...
jgr7 Posted May 9, 2004 Report Share Posted May 9, 2004 Here in Calif. when the winter blend of oxyginated fuel first came out there were lots of car fires and reduced fuel economy too. Now we have the same crap fuel all year although the car fires are down( burnt all the ones with bad fuel lines up) we still have this poison that they put into the fuel and charge us more than anywhere else in the states, and we can't buy from outside Calif. because of the regulations on our fuel. When a refinery goes down the price spikes up. The additive is MTBE formerly a hazardous waste that the oil companys had to pay big bucks to dispose of, now we pay big bucks to them to use it. Also one other little benefit to MTBE is that it is poisoning our under ground drinking water here and now we get to pay to clean it up too!!! BOHICA Jeff Link to comment Share on other sites More sharing options...
67coupedeville Posted May 9, 2004 Report Share Posted May 9, 2004 This may sound off the cuff, but check your gas cap. If it's worn it can cause fuel consumption to increase. Jim White I am just wondering, how do you tell if your gas cap is pooched? When I open the gas cap on my 91 Fleetwood, there is a hissing sound that lasts for a couple seconds. Is this a sign of a worn gas cap or is this normal? Thanks for any help! Spence Link to comment Share on other sites More sharing options...
Ranger Posted May 9, 2004 Report Share Posted May 9, 2004 If it's hissing, I don't think it is working right. It is basically a check valve. It will let air in to replace fuel that is used but will not let air backout. If you are hearing a hissing, that means there is a vacuum created which means that the cap is not letting air in. NOT GOOD If the fuel is not being replaced with air, something has to give. Either the pump will stop pumping when the vacuum gets too great or the tank will cave in. Link to comment Share on other sites More sharing options...
Marika Posted May 9, 2004 Report Share Posted May 9, 2004 If you live in an area that is required to use the new RFG type fuels you WILL experience a decrease in gas mileage. I found this site: http://www.tnrcc.state.tx.us/air/ms/rfg.html from which I quote: Using RFG The exhaust emissions of vehicles using RFG will have less air toxins and ozone-forming pollutants, and the RFG should have no adverse effects on vehicle performance or the durability of engine and fuel system components. However, there may be a slight decrease in fuel mileage (one to three percent) due to the higher concentrations of oxygenates. To me, it makes no sense to reduce air pollution by making a person fill their tank up more often. The more fuel you use, the more you pollute the environment. As a result, if you used (for example) 1,000 gallons of fuel in your car for one year and will now have to use one to three percent more fuel to attain the same mileage for the year, not only do you have to spend more money to achieve the same mileage, you will be adding that many more pounds of pollution into the atmosphere because of the burning of the addtional fuel. The only thing that's clear to me is that ExxonMobil just posted their highest profits in thirteen years because of this newly reformulated gasoline. More fuel sold means the government is collecting more fuel taxes. Ah, those old bedfellows are at it again. If you really want to make people safe drivers again then simply remove all the safety features from cars. No more seat belts, ABS brakes, traction control, air bags or stability control. No more anything. You'll see how quickly people will slow down and once again learn to drive like "normal" humans. Link to comment Share on other sites More sharing options...
CANADIANCADDY Posted May 9, 2004 Report Share Posted May 9, 2004 In the event it hasn't been mentioned yet you might also want to check your oxygen sensor although I too believe you may well need new plugs wires and filters etc. Link to comment Share on other sites More sharing options...
jgr7 Posted May 9, 2004 Report Share Posted May 9, 2004 In Calif. if your cap won't hold pressure you won't pass smog inspection, even if you are within specs on the treadmill. It is part of the test they take your cap off and pressure test it on a machine. They will gladly sell you a $15 cap on the spot to get you out the door!!! Mine always hiss on a low tank warm day. Jeff Link to comment Share on other sites More sharing options...
KHE Posted May 10, 2004 Report Share Posted May 10, 2004 If it's hissing, I don't think it is working right. It is basically a check valve. It will let air in to replace fuel that is used but will not let air backout. If you are hearing a hissing, that means there is a vacuum created which means that the cap is not letting air in. NOT GOOD If the fuel is not being replaced with air, something has to give. Either the pump will stop pumping when the vacuum gets too great or the tank will cave in. I don't think the hissing is a bias for replacing the fuel cap. My Fleetwood Brougham has hissed when I remove the gas cap since the day I drove it off the lot with 15 miles on the odometer... The fuel systems are very tight on modern cars. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
tjtjwdad Posted May 10, 2004 Report Share Posted May 10, 2004 I replaced one on my Bronco and it had an immediate impact. Also, the fuel attendent in Oregon didn't give it the "3 clicks" after fueling and on my trip home I noticed a substantial decrease again. As far as the "hissing" sound, I only hear it when the tank is almost empty on a somewhat warm day. Jim Link to comment Share on other sites More sharing options...
CaddyChris Posted May 10, 2004 Report Share Posted May 10, 2004 Don't wind it up to 5000 rpms at every traffic light. HAHA. Christopher Petro 94 sts 67 coupe de Ville Link to comment Share on other sites More sharing options...
Marika Posted May 10, 2004 Report Share Posted May 10, 2004 If it's hissing, I don't think it is working right. It is basically a check valve. It will let air in to replace fuel that is used but will not let air backout. If you are hearing a hissing, that means there is a vacuum created which means that the cap is not letting air in. NOT GOOD If the fuel is not being replaced with air, something has to give. Either the pump will stop pumping when the vacuum gets too great or the tank will cave in. I don't think the hissing is a bias for replacing the fuel cap. My Fleetwood Brougham has hissed when I remove the gas cap since the day I drove it off the lot with 15 miles on the odometer... The fuel systems are very tight on modern cars. I think we had this discussion on another thread but basically, you should replace your cap "every so often". When I bought my '92 Seville, I began to notice the engine would "jitter" once in a while during idle. I changed the gas cap and BINGO, it was gone. If you really want to make people safe drivers again then simply remove all the safety features from cars. No more seat belts, ABS brakes, traction control, air bags or stability control. No more anything. You'll see how quickly people will slow down and once again learn to drive like "normal" humans. Link to comment Share on other sites More sharing options...
Marika Posted May 10, 2004 Report Share Posted May 10, 2004 Don't wind it up to 5000 rpms at every traffic light. HAHA. Apparently, that IS a habit a lot of Cadillac owners have; they like to do WOT. The 4.9L engine doesn't need it, and I don't do it. If you really want to make people safe drivers again then simply remove all the safety features from cars. No more seat belts, ABS brakes, traction control, air bags or stability control. No more anything. You'll see how quickly people will slow down and once again learn to drive like "normal" humans. Link to comment Share on other sites More sharing options...
JasonA Posted May 10, 2004 Report Share Posted May 10, 2004 The 4.9L engine doesn't need it, and I don't do it. All engines can benefit from it, and your 4.9 is begging for it! WOT simply means Wide Open Throttle. Or put plainly, flooring it. It's good for an engine to work it out...that's what its designed for. It doesn't like idling around all day; let it open itself up! Remember, by pressing the gas pedal further, you're not "pushing" it harder, you're just allowing the engine to achieve it's potential. The purpose of a throttle is to restrict airflow to an engine to achieve a specific speed or power level. Give it some more gas and you're just letting it run "less restricted". Jason(2001 STS, White Diamond) "When you turn your car on...does it return the favor?" Link to comment Share on other sites More sharing options...
Marika Posted May 10, 2004 Report Share Posted May 10, 2004 The 4.9L engine doesn't need it, and I don't do it. All engines can benefit from it, and your 4.9 is begging for it! A cadillac never begs. If you really want to make people safe drivers again then simply remove all the safety features from cars. No more seat belts, ABS brakes, traction control, air bags or stability control. No more anything. You'll see how quickly people will slow down and once again learn to drive like "normal" humans. Link to comment Share on other sites More sharing options...
JohnnyG Posted May 11, 2004 Report Share Posted May 11, 2004 I think Greenpeace is behind it! If those darn tree hugging Californians wouldn't have complained so much about clean air, none of us would have oxygenates in our fuels right now. When you deal with the government, you can just throw logic out the window. Nobody is immune from the reaches of govt. regulations, not even oil companies. In fact, those "rich oil companies" used to be the prime candidates for squeezing money out of. Not much has changed on that front. Now, the tree huggers are at it again, low sulfur gas, which we have now. By 2006 it will be "Ultra Low Suphur" diesel, so the cost of diesel fuel will go up too..dramatically. Diesel trucks will be equipped with catalytic converters, just like cars. With those price increases for trucking, food prices will climb, etc. I'm betting on a truckers strike in the near future, just like in 1976. Homeland Security has it's hands in the oil companies pocket right now as well. I will be installing new lighting, security cameras, fencing, guard service, writing a security plan, you name it. The Al queda is behind it, and that was their plan from the beginning. Just as Bin Laden was surprised when the towers fell, so will he be surprised at how quickly his main objective is being realized....the destruction of the U.S economy. We all need to do our part to defeat the enemy every chance we get. Griping about prices won't help. Ride a bike, or a horse or something. "All it takes for evil to succeed, is for good men to do nothing" Sorry for the politics, I probably broke all of the posting rules with this one. I'm just tired of getting the brunt of all the anger. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
MIke D Posted May 11, 2004 Report Share Posted May 11, 2004 Someone once told me.. "to get better gas mileage, take the wallet out of your back pocket".. well I never put my wallet back there, so I just moved my seat back a few more inches... Now I cant press the gas so hard anymore... On a different note... How do you tell when an O2 sensor is bad. I have 196,000 miles and have not changed them yet. BTW My city mileage is 14-15MPG... It used to be better before I changed tires and exhaust... MD Cop didn't see it, I didn't do it! 93 STS 225,000 Miles 99 STS 111,000 Miles Link to comment Share on other sites More sharing options...
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