Penix Bowties Posted December 20, 2004 Report Posted December 20, 2004 The car: 1996 Oldsmobile Cutlass Supreme SL 3100 SFI When I first got the car last year I was getting a bit over 400 miles per tank, then I had an intake gasket go bad on me and coolant got into the crank case. At first I wasn't sure what was go'n on, but then it started to overheat. After I got it home and let it cool down, I filled it up again to see where the water was go'n. Shortly after this the lifters began knocking and the oil looked like foam. Some of the water made it's way through the exhaust system via the PCV valve once the car was up to operating temp and the water turned to steam. That was then... This is now... I had the engine flushed, I had the coolant system flushed, I had the lifters and pushrods replaced, I had new gaskets installed and I went ahead and got a complete tune up. The engine was running VERY smoothly, sounded like new, aside from a mild exhaust leak due to a cracked flex-tube. At this point I was getting an average of around 230 miles per tank. I built a ram air setup using 4" O.D. plastic tubing and two intake ports under the front of the car. I also replaced the new FRAM air filter with a K&N air filter. This added a nice bit of power and got me around 270 per tank. I replaced the flex-tube and cat, and while I was at it replaced the stock muffler with a Delta Flow 50-Series and Magnaflow double walled SS tip (4"Lx3"IDx3.5"OD). This got me up to where I am now, around 300 miles per tank, with plenty of power! Though I feel the power gained from all this, and though the engine runs smooth as silk, I still feel like it's running rich or something. I'm missing over 100 miles per tank and it should still be producing more power than this. And no, there are no lights come'n on and all the sensors are new. Any ideas? Thanks! - Joel Penick Quote
OldsmoBeast Posted December 20, 2004 Report Posted December 20, 2004 I only ever get around 200 - 250 miles per tank in my 97... Quote
sl3196 Posted December 20, 2004 Report Posted December 20, 2004 My old 96 3100 cutty would get 370-400 miles per tank on the highway everytime. Are you doing alot of city driving or idling for long periods of time? Quote
OldsmoBeast Posted December 20, 2004 Report Posted December 20, 2004 My old 96 3100 cutty would get 370-400 miles per tank on the highway everytime. Are you doing alot of city driving or idling for long periods of time? Yes, and yes. And I have a pretty heavy foot...especially right at 50 km/h where it'll downshift into 1st... I love that spot.... Quote
sl3196 Posted December 20, 2004 Report Posted December 20, 2004 That would explain it then. My GTP gets around 200-250 miles a tank when I go racing/crusing in town. Quote
OldsmoBeast Posted December 20, 2004 Report Posted December 20, 2004 That would explain it then. My GTP gets around 200-250 miles a tank when I go racing/crusing in town. Oh well... I just hope I can get my car running again soon so I can actually drive those 200-ish miles per tank... Its been like two weeks and I haven't really done much... Need an impact gun to get my head bolts loose... Quote
Penix Bowties Posted December 20, 2004 Author Report Posted December 20, 2004 Normal driving conditions, which means mostly freeway. However, the difference in how many miles I get per tank doesn't seem to change much between normal driving conditions and play'n around some, maybe a 25-30 MPT difference. Could it possibly be a bad injector or something else related to the injection system? I'm gonna run a dye test on it when I get back in town. Even though I don't see any obvious leaks and I'm not smell'n any fuel I figure I might aswell just check to make sure. Any more input guys? Thanks! - Joel Penick PS: When I get back I'll take some pics of my ram air setup, but I'll need someone to help me post them, seeing how I've never posted pics online before. I do have a scanner so that makes it somewhat easier. Quote
maybe2fast Posted December 20, 2004 Report Posted December 20, 2004 between highway and city driving milage is huge Quote
sl3196 Posted December 20, 2004 Report Posted December 20, 2004 between highway and city driving milage is huge Sure is! My GTP gets 17/20 mpg in town and 26/28 on the highway. Quote
Brian P Posted December 20, 2004 Report Posted December 20, 2004 I get between 310-350 miles on about 14 gallons. LI driving, which I do 60% "highway". I only see 400+ if I'm driving 100% highway outside of Long Island. So you shouldn't be seeing 400 miles unless you're all highway. Quote
Mizouse Posted December 21, 2004 Report Posted December 21, 2004 I had a similar thing going on with my old 96 Cutty. I was getting about 320 to a tank (which was about 70% highway driving). Then the mass air flow sensor got replaced and the mileage bumped up to almost 380 to a tank. Go figure. Quote
phantomshado Posted December 21, 2004 Report Posted December 21, 2004 Oh man, over the summer, I established well over 500 miles (potsdam to manlius to rochester to manlius to potsdam and some tooling around) I think my total before I was REALLY worried about running out of gas was about 523 or something like that. Thats about 502 pure highway miles, so thats where that number was achieved. I have a slightly heavy foot, not as heavy as some, but I'm no slouch. My theory is the K&N intakes. More air past the MAP, means more fuel is going to be dropped proportionally. None of us reprogram the ECM after something like that, which really doesn't affect us other than getting poorer gas mileage. Thats just my theory. Quote
Stealth Posted December 22, 2004 Report Posted December 22, 2004 the computer automaticaly adjusts teh air fuel ratio you shouldnt be getting lower milage you should be gettign higher milage with a new intake. also Im only getting like 330kms a tank or like 212 miles which is horrible Quote
Guest Gp crazy Posted December 22, 2004 Report Posted December 22, 2004 Well, mine is a 1990 GP STE and I only get 314--330 miles on 14.7 gal. Most of my driving is highway. I do not idle a lot nor do I drive a lot in the city its about 80% highway and 20% city. the most I ever got with a GP auto or stick is 330 miles to a tank. On a trip we had 4 people that avg. weight of 220 lb. + all your gear for a two week road trip. We traveled at 75-110 mph. 75-90 mph most of the time! I do not think that 330 mpt is to bad for a mid sized car with a 2.8,3.1,3.4doch,3100 or a ram air push rod 3.4,3.8 I II III with a 4 speed auto or a 5 speed stick! 8) that is my in put Merry Christmas (: to all Quote
pitzel Posted December 22, 2004 Report Posted December 22, 2004 Oxygen sensor replacements are *mandatory* after an intake gasket failure. Especially if your oil got so bad that it was foaming. That would be where I would look first. Also, the cold weather sure does reduce mileage. Quote
CuttySup Posted December 23, 2004 Report Posted December 23, 2004 300 miles per tank. Consider yourself lucky. I only drive around town and get a little over 200 miles per tank at 13mpg Quote
terryk2003 Posted December 23, 2004 Report Posted December 23, 2004 300 miles per tank. Consider yourself lucky. I only drive around town and get a little over 200 miles per tank at 13mpg :shock: DAMN DUDE!!!...i was upset with my 19mpg driving around town...i guess i should be happy with that... Quote
Tru2Chevy Posted December 23, 2004 Report Posted December 23, 2004 I can get 375 - 400 miles out of one tank in my '91 Lumina (3.1, 3spd auto, no lockup). I can make it from Trenton(NJ) to Pittsburgh on less than 3/4 of a tank And that is with plugs and wires that have 60,000+ miles on them, and the original o2 sensor (175,000 miles). I think my car is some kind of freak..... - Justin Quote
justa6 Posted December 23, 2004 Report Posted December 23, 2004 rememebr the time of year also. for us in the cold weather, they change the fuel at the pumps, and the gas has more ethonol in it, wich makes for worse gas milage. i noticed a decrease in mine as soon as it got cold and they started usign the winter mixutre. i think the last tank (purely city) i had like 250, but on the highway, i still get over 350 and thats with a butload of miles! (205,000) Quote
phantomshado Posted December 23, 2004 Report Posted December 23, 2004 what size tank is everyone rocking? mine is 16.5 gal. Quote
Stealth Posted December 23, 2004 Report Posted December 23, 2004 arent all the tanks the same size? Quote
Penix Bowties Posted December 27, 2004 Author Report Posted December 27, 2004 I'm runn'n around a 16 gallon tank... Well, I had a feeling it was a bad O2 sensor or two, and it looks like I might be right. My mechanic, who also happens to be my best friends dad which I've known since I was 3, told me that if was the O2's then the "Service Engine Soon" light would probably come on shortly after if not right after the exhaust work was done. Sure nuff, "S.E.S." light just came on. I'll be take'n my car in Wednesday if all goes well, and I'll post our findings. On another note, I know I said I'd post pics of my ram air setup as soon as I got back but it's gonna be a bit longer than I thought. Somone stole the inlets off my car while I was gone, so I'll have to order new ones from RamAirBox.com... Merry Christmas to me I guess. Sorry guys! Anyhow, in the mean time I think I'm gonna clean up the setup, maybe paint it too while I'm at it. Merry Christmas Y'all! - Joel Penick Quote
Brian P Posted December 27, 2004 Report Posted December 27, 2004 you'll be even happier to know that O2 sensors usually cause poor performance and get "lazy" before they set off a code. Especially pre-OBD2. Quote
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