allenshane Posted September 12, 2011 Report Share Posted September 12, 2011 i got 320 miles on a full tank when i got this car a few months ago and every tank after that i am only getting 220 miles on one tank when i should be averaging 20mpg....right now i am getting less then that......less than 17 iis what i am getting and that is the lowest its supposed to get..............all filters are good and new.......i change oil every 2,000 miles......my idle is kinda weird it flucuates between 500 and 1500 rpms about 40 to 50 percent of the time and yes the fuel pressure is fine.............could not having a perfectly air tight muffler/exhaust be the problem?????/help me out i want my 320miles on a tank back :mad::mad::mad: Quote Link to comment Share on other sites More sharing options...
94 olds vert Posted September 12, 2011 Report Share Posted September 12, 2011 3.1l? I just filled my GP up. My DIC tells me 380 miles on this tank. I'm currently getting 23 mpgs. I do not know if that is true as I've only put 30 miles on this car. Check the PCV valve. IAC, clean the throttle body. Also check for vacuum leaks. Quote Link to comment Share on other sites More sharing options...
Andrew Posted September 12, 2011 Report Share Posted September 12, 2011 the idle fluctuation could definitely be the issue if its a vacuum leak. its likely a sensor issue though. the muffler is not the problem. other potential items to inspect are the spark plugs, o2 sensor, and cat converter. Quote Link to comment Share on other sites More sharing options...
allenshane Posted September 13, 2011 Author Report Share Posted September 13, 2011 i will check those in a couple days.....ill let you guys know Quote Link to comment Share on other sites More sharing options...
allenshane Posted September 13, 2011 Author Report Share Posted September 13, 2011 mmm......this will sound stupid enough comming from me but how exactly you check for vacuum leaks and where.....i am pretty car savvy but some things i just dont get Quote Link to comment Share on other sites More sharing options...
Mel87 Posted September 13, 2011 Report Share Posted September 13, 2011 I don't get good MPG... probably cause of the heavy foot Quote Link to comment Share on other sites More sharing options...
Andrew Posted September 15, 2011 Report Share Posted September 15, 2011 look. listen, and feel. if you dont find any that way, spray some starting fluid around the vac line ends while the engine is running. if it idles up, you have a leak. Quote Link to comment Share on other sites More sharing options...
pitzel Posted September 24, 2011 Report Share Posted September 24, 2011 (edited) Check the O2 sensor for sure, and replace it if it is of unknown age/condition. Your overly frequent oil changes could very well be causing significant contamination or performance degradation. O2 sensors are very sensitive to the 'stuff' that is in motor oil that volatilizes during the first few thousand miles of operation. Ideally, go with a good synthetic oil (ie: Mobil-1, Esso XD-3 0W-30, etc.) and change it very infrequently. I personally have only changed my oil once in the past 9 years of owning this car, and that was because I had to re-do the LIM and there was coolant contamination. Doing lots of oil changes when they're not necessary is just inviting trouble for exhaust-gas path instrumentation/systems, and even catalytic converter. BTW, 500 miles almost every tank here, when I keep it at 60-65mph, in the 3.1L 1992 Cutlass Supreme, which should be identical engine-wise to yours. Do you have the 3-speed by any chance (ie: without the overdrive gear?)? I believe lots of Luminas received at instead of the full-blown 4T60, and efficiency will definitely suffer. Edited September 24, 2011 by pitzel Quote Link to comment Share on other sites More sharing options...
Andrew Posted September 24, 2011 Report Share Posted September 24, 2011 he's out of his mind if he thinks 1 oil change in 9 years is good. Quote Link to comment Share on other sites More sharing options...
pitzel Posted September 24, 2011 Report Share Posted September 24, 2011 (edited) Nope, when I had the engine apart to do the LIM, there was no sludge whatsoever (at ~40k mi since the previous oil change!). Just make sure you use a decent synth oil (I gave a few suggestions). These 3.1L engines are notoriously easy on oil. Of course, the engine will probably leak a quart every 10k miles out, so make sure you're replenishing as required. Frequent oil changes, as I argued, actually cause damage to components. Especially if you're using the cheapest oil you can find. Phosphorous offgassing is at its highest rate when oil is brand new -- so if you're always putting brand new oil into the car, you're always hitting the O2 and cat with high levels of volatilized ZDDP additive, among other contaminants, which accelerates their degradation dramatically. Edited September 24, 2011 by pitzel Quote Link to comment Share on other sites More sharing options...
jman093 Posted September 24, 2011 Report Share Posted September 24, 2011 Quote Link to comment Share on other sites More sharing options...
pitzel Posted September 24, 2011 Report Share Posted September 24, 2011 Nope, not trolling. A guy on bobistheoilguy.com who runs the 3.1L GM V6 engines in taxicabs studied the issue and found 40-50k mi OCI's were perfectly appropriate (if not a bit on the conservative side) using used oil analysis. I merely applied the same science and logic to my engine with a good quality synthetic oil. And at the teardown 60k into the oil change (because of a LIM leak), there was no sludge or abnormalities on any upper engine components. I'm now 100k km's into the regime, 9 years, still, no issues. If you figure $30 an oil change, I've already saved 18 oil changes (ie: twice a year, or once every 3000 miles). 18 * 30 = $540. Heck, the car is only worth $2k, so why throw a bunch of money needlessly into it, especially since the long oil change intervals are proven to work? And obviously less oil changes causes less degradation of gas path sensors and catalysts. Quote Link to comment Share on other sites More sharing options...
white4d96 Posted September 24, 2011 Report Share Posted September 24, 2011 Nope, when I had the engine apart to do the LIM, there was no sludge whatsoever (at ~40k mi since the previous oil change!). Just make sure you use a decent synth oil (I gave a few suggestions). These 3.1L engines are notoriously easy on oil. Of course, the engine will probably leak a quart every 10k miles out, so make sure you're replenishing as required. Frequent oil changes, as I argued, actually cause damage to components. Especially if you're using the cheapest oil you can find. Phosphorous offgassing is at its highest rate when oil is brand new -- so if you're always putting brand new oil into the car, you're always hitting the O2 and cat with high levels of volatilized ZDDP additive, among other contaminants, which accelerates their degradation dramatically. Except ZDDP hasn't been in road-legal motor oil for over 5 years. Hence why so many people have issues with flat tappet cams getting destroyed with modern oils. Quote Link to comment Share on other sites More sharing options...
pitzel Posted September 24, 2011 Report Share Posted September 24, 2011 (edited) Except ZDDP hasn't been in road-legal motor oil for over 5 years. Hence why so many people have issues with flat tappet cams getting destroyed with modern oils. Exactly. They had to remove it because too many idiots were changing their oil every 3000 (which is contrary to nearly all manufacturers' recommendations), and wrecking their instruments and catalysts prematurely. Excellent additive, but the dum-dums who changed their oil overly frequently ruined it for the rest of us. They're actually finding on some of the new direct injection petrol engines, that the overly-frequent oil changers have major intake valve deposits, traceable back to the oil. Again, idiots not reading the manuals, and thinking that changing oil is a good thing. Edited September 24, 2011 by pitzel Quote Link to comment Share on other sites More sharing options...
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