95SevilleSLS Posted March 7, 2007 Report Share Posted March 7, 2007 So I've been getting about 13 MPG all city driving since I got this 02 STS. I figure that's decent since the temperature around here has been between -10F to 20F and I let it warm up a lot. I just took it to my parents (65 miles away) and the temperature was 12F and I only got 19 MPG. That, I think, isn't very good. It was all highway going about 73 MPH. Does the cold really make that big of a difference? Why would it be that bad, I'm sure the spark plugs haven't been changed, but they aren't causing any problems and replacing them sure isn't going to get the MPG up to 27 like they are rated for. I may get a 2 MPG boost at best. I know it's a used car and it won't get "as good." But I had a 95 SLS that was rated for 25 MPG and at 140,000 miles it got 24.5 MPG on the highway going 78 MPH. Here is a little in info on what I've done for it in the past month: changed oil and filter, changed the air filter, and did a couple of WOT's. Is anyone else getting this crappy of mileage? -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
Cadillac Jim Posted March 7, 2007 Report Share Posted March 7, 2007 Only with heavy traffic and a lead foot with regular gas. With light traffic and a light foot, I get 23 mpg using 93 octane gas. That's with the Touring package, which you ave with the STS. The SLS will get a little better gas mileage, particularly with a very light foot. Best gas mileage with Northstars is to be had in the 60 mph to 75 mph range, so you're good at 73 mph. One factor that can make a big dent in gas mileage at low temperature is stops. Any car gets poor gas mileage when cold. If you stop for food or whatever and the car cools off, you will dent your gas mileage. Set the DIC to read out instantaneous gas mileage and watch it while you drive, and you will see what I mean. At a 73 mph cruise, steady speed, steady foot, level ground, and no wind, you should see a readout of 26 mpg or better. If you don't, keep looking. -- Click Here for CaddyInfo page on "How To" Read Your OBD Codes-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data -- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC Yes, I was Jims_97_ETC before I changed cars. Link to comment Share on other sites More sharing options...
JasonA Posted March 7, 2007 Report Share Posted March 7, 2007 Ambient wind direction/speed also plays a HUGE factor. If you're driving 73 mph into a 20 mph headwind, the car is "seeing" an aerodynamic speed of 93 mph...that kills mileage. Miles on the car shouldn't play a huge factor. Even with 156,000 miles, my '97 SLS returns between 27-30 on highway trips, and 20 in town. I haven't had my '01 long enough to get a true mpg average, but on the 2 hour drive back home from Greensboro where I bought it, I averaged about 31 mpg, and driving around in town, I'm averaging 18-20...so very close to what my SLS got, which very much surprises me. And that's on regular fuel (which is what a 2000+ vehicle takes). I'm running a tank of midgrade now, and may even try premium just as an experiment to see if there's any gain in mpg or performance. Check the spark plugs, check the PCV valve, check the air pressure in your tires. The cold temperatures by themselves won't usually hurt gas mileage that much, but some of the ancillary effects as Jim mentioned above can hurt. 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...
weephee Posted March 7, 2007 Report Share Posted March 7, 2007 I have a 2002 STS and just did a return trip from Ottawa, Canada to Florida which was a 1300 mile trip each way. When I left Ottawa, the temp was about -20 F. The first day I drove just over 600 miles and ended up in Ricmond, Kentucky. This was all highway miles except for going through customs in Detroit. Average mpg was 23. From Kentucky down to Florida the temperature obviously increased as I drove south and I would guess the average temp on the 2nd leg of the trip was 45 F. The average mpg on the 2nd day was 25.4 mpg. I drove 8 to 10 mph over the speed limit all the way down so I would guess my average mph was 60. Car was loaded with baggage because my wife was with me. That's my experience. I would look at tire pressure, air cleaner, plug gaps. Other then that not much else you can do. Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 If anything the dense cold air is better. Did you reset your DIC, ie fuel, average miles per gallon and average speed before your trip? If not the system is simply pulling up your local figure..... Make sure your tire air pressure is 32+ Needing a tune up could cause a lower MPG Also using regular and having 10% ethanol hurts mileage Check to make sure your TCC is going into OD by driving highway speed (60), watch TACH, keep foot on gas, and press brake with your left foot, RPM should increase 150 to 200 RPMs..... if not your TCC is NOT engaging... Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 Thanks for all the replies! I'm going to try to answer everyone in one shot. I didn't use the DIC to figure out mileage, I never trust those. I went and filled up at a gas pump went to my parents, came back and filled up in the same spot. The pressure in my tires is 33 psi. My air filter is new. I haven't checked the pvc (I'll buy a new one today, but where is it located?) I know my TCC is locking up because I have felt it lock up in 3rd (around town) and on the highway, and I have felt it unlock a couple of times when I drive in hilly areas. There was barely any wind when I went. I very much don't have a lead foot around town, I drive like a gramps. I checked the DIC while I was driving down the highway on a flat surface and the instant was 19 MPG. I was hoping it was lying, but it wasn't. I only made one stop on the trip and that was at my parents. I didn't plan on putting spark plugs in so early because GM says that you don't have to replace them till 100,000 miles. I'll probably just pull one today to see how shape it's in and see if the gap is right. I used regular gas from BP, no ethanol crap. -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
JimD Posted March 7, 2007 Report Share Posted March 7, 2007 A couple of points that will not help with your actual MPG, and one that might. I doubt if you will find a PCV valve on your engine. The instantaneous, and therefore the average, MPG indication on the DIC is much more accurate than you trying to fill the tank to exactly the same level each time you refuel. The PCM knows exactly how much fuel should be flowing through the injectors at all times and how far the wheels have rolled. Perhaps some of your fuel is not flowing through the injectors, or fuel is flowing through the injectors when the engine is not running? Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 First off, TRUST the vehicles information center TOTALLY! Its extremely accurate. The system calculates it based on fuel injector pulse counts and pulse width. The PCM counts the pulses and does the math. I may be over simplifying it but I believe that is basically how it works. You must reset it before your trip for it to be accurate for the entire trip. Miles per gallon are a blend of highway and local driving to create the average... The BIG question is what was you AVERAGE MILES PER HOUR for the entire trip?.... you will be amazed how much local driving negatively impacts your average miles per gallon... and how the average miles an hour negatively impacts it.. If you used the system you would have all the information you needed to understand the average miles per gallon... Right now? if i asked you what was your average miles per hour? you can't accurately answer that..... Use it next time... Try it again, if in fact you did 73 for the entire trip with little or NO local driving (we can't know the average MPH accurately right now), I think your average MPG is low, you could have a leaky injector or leaky fuel pressure regulator... Check the mileage again with the on board system the and report your findings.. BY THE WAY, OD is a 4TH gear NOT a 3RD gear..... Check the TCC again as I detailed above...using the brake and looking for the RPM increase... Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
thu Posted March 7, 2007 Report Share Posted March 7, 2007 I drive between 80 and 90mph. I drive 40 to 45 miles at a shot. When it gets that cold (-10*F to 20*F), I get between 19 and 21. This is when I use *any* grade of fuel. I use regular (85 octane) mostly. When it warms up, the economy goes up to 22-24. 2003 Seville STS 43k miles with the Bose Sound, Navigation System, HID Headlamps, and MagneRide 1993 DeVille. Looks great inside and out! 298k miles! Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 I did check the DIC when I was going down the highway though and it was 19 MPG instant and I left it on for a long time. So I did get that bad mileage. This is north dakota, there was not city driving to get to my parents, it was just there and back all highway. As you said, trust my DIC, which was saying that I was getting 19 MPG. Yes, the TCC does lock up in 3rd and 4th. I worked at a tranny shop for about 3 years, that's what it does. Watch your tach going about 35 or so, you'll see it jump down quite a bit, that's the torque converter locking up. Then if you drive a little faster it will shift to 4th, then your TCC will lock up again at about 45-50. I'll pull my plugs today to see what shape they're in. Someone put up-gapped spark plugs in my suburban once, maybe they did that to this too. -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 If that's the case, I didn't know that the TCC could lock up in third, typically the TEST is drive highway speed and tap the brake to see if RPM increases. I have always considered TCC lockup as a 4th gear. Here is a table, Poor Fuel Economy for your 2002 Seville, Mike Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 Yes sir, it locks up in 3rd too. You can do that same test when it locks up around 35 or so. You can touch the brake and the rpm will jump up. Thanks for the table, but...that will take me a few years to test everything I'll start with the plugs, I think that's probably the easiest thing for now. -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 Agreed, but I just wanted you to have it, since the chart was specific to the 'problem' you are possibly having. Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 So I went to take out a spark plug to see what kind of shape they were in. It's a little different getting to the spark plugs on an 02 than a 95. It's kind of nice though, you don't have to replace wires on an 02. Ok, so here are some pictures. The gap was .050 just like it was supposed to be. It doesn't look like they've been changed. What do you guys think, should I replace them? -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 Check for the platinum pads, it looks like that one is intact... we have seen the plugs lose the pads How do you feel about Denso plugs vs the AC DELCO? We tend to like AC DELCO as aftermarket plugs are problematic.. Those aren't the original plugs Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 Never really thought about denso. I wonder when they were replaced... I can get AC Delcos for $5.47 a piece. I was also thinking about champion plugs. They are $4.49 a piece for the double platinum and $2.99 for the platinum. Do you think I should stick with AC delco? Should I probably replace them? Sorry, I forgot to mention in the beginning that I changed the fuel filter too. -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 Never really thought about denso. I wonder when they were replaced... I can get AC Delcos for $5.47 a piece. I was also thinking about champion plugs. They are $4.49 a piece for the double platinum and $2.99 for the platinum. Do you think I should stick with AC delco? Should I probably replace them? Sorry, I forgot to mention in the beginning that I changed the fuel filter too. Here is an interesting thread, its possible that Denso makes AC Delco.... http://caddyinfo.ipbhost.com/index.php?sho...05&hl=denso See this one: http://caddyinfo.ipbhost.com/index.php?sho...ic=6330&hl= I would either use AC Delco or Denso..... knowing me however, I'd would lean toward AC Delco... regardless of cost... Check http://www.gmotors.com for parts or http://www.rockauto.com Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
JasonA Posted March 7, 2007 Report Share Posted March 7, 2007 Concur, I would stick with ACDelco. 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...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 Interesting...so those could possibly be my original plugs. It started snowing, and I don't have a garage, so I had to put everything back together. Stupid North Dakota weather. Just 180 miles south west of us in Medora they are sitting at 50 right now. Suppose to almost hit 70 this weekend for them. Anyway, back to the plugs. I'm probably going to replace them tomorrow or the next day if it gets a little warmer and STOPS SNOWING! -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 My gut tells me that they are not original but they might be an adequate replacement... I doubt that the factory would install Denso... How many miles are on your car?, if those are not the original they look pretty funky... Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
JimD Posted March 7, 2007 Report Share Posted March 7, 2007 My '04 has OEM ACDelco 41-987, GM 12571535 plugs installed. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 My gut tells me that they are not original but they might be an adequate replacement... I doubt that the factory would install Denso... How many miles are on your car?, if those are not the original they look pretty funky... There is 81,230 miles on the car. I should have pulled a few more to see what the others looked like, but it started to snow. I'll probably do some more looking around this weekend when I lube my intermidiate steering shaft on it too. -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 7, 2007 Report Share Posted March 7, 2007 My gut tells me that they are not original but they might be an adequate replacement... I doubt that the factory would install Denso... How many miles are on your car?, if those are not the original they look pretty funky... There is 81,230 miles on the car. I should have pulled a few more to see what the others looked like, but it started to snow. I'll probably do some more looking around this weekend when I lube my intermidiate steering shaft on it too. Definately post some info on how you go about lubing the intermediate steering shaft and any tips, Thanks Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 7, 2007 Author Report Share Posted March 7, 2007 Maybe I'll spend a little extra time and take some pictures along the way. -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
Ed Hall Posted March 7, 2007 Report Share Posted March 7, 2007 My 93 Northstar powered Allante also suddenly dropped in gas mileage. After several weeks of driving, a code came up and turns out, one of the O2 sensors was bad. Now I get 27 mpg on the highways. Link to comment Share on other sites More sharing options...
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