1BADVR4 Posted December 9, 2005 Report Share Posted December 9, 2005 Well I figured I would post a little tutorial up here with my experiences with my new GTP and gas mileage. Poor gas mileage is often a very difficult problem to diagnose without DTCs being set. I will be going through a series of steps to improve the gas mileage on my GTP and hopefully help a few people out in the process. Specs: 2000 GTP Sedan 110,000 miles Step 1. COMPLETED Change the oil. It has had mobil 1 since 20,000 miles so it's pretty clean, but this might help a microscopic amount. Step 2. COMPLETED The car's first tank got about 200 miles to 3/4 of a tank when the fuel pump died. I figure it was getting about 16 mpg. I put a new fuel pump in and it started right up, however, the pump was whining like crazy. Today I replaced the fuel filter and the pump quieted down immediately. I can only imagine that a restricted filter burned out the pump. And weak fuel pressure was causing poor gas mileage. I have found several other things wrong and as I fix them I will note the results and the gas mileage. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted December 9, 2005 Report Share Posted December 9, 2005 from what i've seen some simple mods will even help them get crazy nice gas mileage, i ha ve a friend with a VERY built 97' GTP, and on the highway he can pull off 35 or so according to the DIC Quote Link to comment Share on other sites More sharing options...
corning_d3 Posted December 9, 2005 Report Share Posted December 9, 2005 Man, and i thought 31 mpg was good mileage with my '96 monte... Quote Link to comment Share on other sites More sharing options...
john99gtp Posted December 9, 2005 Report Share Posted December 9, 2005 35mpg on a gtp? not only that, but a modded gtp? im sorry, but BS flags gonna raise here Quote Link to comment Share on other sites More sharing options...
pwmin Posted December 9, 2005 Report Share Posted December 9, 2005 dont be a dick, especially when you are wrong! most L67's i know that have certain mods get better mpg. my riv did with the mods i had Quote Link to comment Share on other sites More sharing options...
Turbo231 Posted December 9, 2005 Report Share Posted December 9, 2005 Believing the DIC is like believing the gas gauge...don't. Fill the tank....drive....Fill the tank. Miles divided by gallons...that's MPG. No "I went this far on a tank" or "The computer says so."...simple math wins everytime. Quote Link to comment Share on other sites More sharing options...
LukeZ34 Posted December 9, 2005 Report Share Posted December 9, 2005 That's what the DIC says though.. has he actually calculated it after filling the tank? Quote Link to comment Share on other sites More sharing options...
john99gtp Posted December 9, 2005 Report Share Posted December 9, 2005 if your riv did it, please tell me what these godly mods were, because damn, i would love to have 35+ mpg on the highway. i know quite a few others that would love to know as well. and on average, DIC is 1-2mpg off (reads higher) so thats around 32-33mpg, but i really want to know what you did. My car does the same as 1BadVR4s just about, 200 miles gets me to about 1/4 tank. I know others that are around the same. If your lucky, you might get 330miles out of a tank (and thats running it bone dry, 70-80 temp, good gas) Edit: cause someone was being an ass about grammar. Quote Link to comment Share on other sites More sharing options...
corning_d3 Posted December 9, 2005 Report Share Posted December 9, 2005 I believe certain mods help milage. After installing ported/polished heads, p/p lower and upper plenums, and exhaust, i went from 25 to 31mpg..... Quote Link to comment Share on other sites More sharing options...
94CutlassSLCoupe Posted December 9, 2005 Report Share Posted December 9, 2005 I have gotten 33mpg observed with an L36...but would never expect that good from an L67. Fuel injector cleaner may improve it a little too since you just put that new fuel filter in. Quote Link to comment Share on other sites More sharing options...
pwmin Posted December 9, 2005 Report Share Posted December 9, 2005 its your not youre (you are) jackass. :lol:i think we discussed this somewhere else i dont care if you dont believe me. i tried helping you out before with a question and you just ignored me so fuck you. i dont care what you think. i know from experience so believe what you want :flip: :kiss: so, out of curiousity, how has your mileage changed from stock to various mods? Quote Link to comment Share on other sites More sharing options...
john99gtp Posted December 9, 2005 Report Share Posted December 9, 2005 I believe certain mods help milage. After installing ported/polished heads, p/p lower and upper plenums, and exhaust, i went from 25 to 31mpg..... it also depends on what else youve done. if youve dropped a 3.25 pulley on there with an intake, the cars grabbing way more air then normal, and it has to compensate by adding more fuel, or else you will go to lean. I believe mods help to some extent, if you do the right ones, and not alot. but a "VERY built 97' GTP" to me implies that more then just basic stuff has been done. ok, maybe im arguing cause im tired, but lets see when i read this tomorrow. Quote Link to comment Share on other sites More sharing options...
1990lumina Posted December 9, 2005 Report Share Posted December 9, 2005 When my friend's dad used to have his Corvette he had some very minor mods done to boost performance a bit and also helped with MPG....I was surpised when I heard this as well, but it's true. Quote Link to comment Share on other sites More sharing options...
Regal_GS_1989 Posted December 9, 2005 Report Share Posted December 9, 2005 Believing the DIC is like believing the gas gauge...don't. Fill the tank....drive....Fill the tank. Miles divided by gallons...that's MPG. No "I went this far on a tank" or "The computer says so."...simple math wins everytime. Yes, that would be the most accurate way to calculate mpg's. But, there is one thing that will make a difference. If you fill it up until the pump says its full, or until its really Full. Because every pump will stop differently. When i want to calculate my milage, I Always fill it right to the top. i have to slowly coax it in, but i can usualy get an extra 2 gallons in there. Our lumina stops so short, that you can always get at least 3 extra gallons in it. I find it hard to believe that there are W's on here that are pulling off 35 Miles per US Gallon on the highway, where mine, is pulling off at most 39 miles per canadian gallon. (US = 3.87 liters, and CAN = 4.5 liters). I dunno,. maybe US fuel gives better milage Quote Link to comment Share on other sites More sharing options...
pwmin Posted December 9, 2005 Report Share Posted December 9, 2005 heavily modded? 35 mpg? i do doubt that. but depends on what heavily modded means. a 1/2mph isnt a lot and realistically what some mods prob would do, but it does add up over time. dont read it tomorrow; im being pretentious right now too. filling it to the top: thats not good, esp for emissions but who cares: not i (well to an extent) Quote Link to comment Share on other sites More sharing options...
Crazy K Posted December 9, 2005 Report Share Posted December 9, 2005 stupid question... what mods are you refering to? Quote Link to comment Share on other sites More sharing options...
White93z34 Posted December 9, 2005 Report Share Posted December 9, 2005 well lets see here, 3.4 pulley, SLP headers, DP, diamond pistions, i forget exactly what his compression ratio is, but i know its higher then factory, 9:5:1 mabie?? mls headgaskets, a intense stage 1 cam, modified DHP pcm code, 160 drilled stat, fresh 4t65e, with better clutches all around, high stall Torque converter, setups got about 3000-4000 miles on it i've been with him in the car and when we are on a flat streatch of highway and he hasen't been goofing off it will pull off 36 or so MPG. at least according to the DIC. Quote Link to comment Share on other sites More sharing options...
skalor Posted December 9, 2005 Report Share Posted December 9, 2005 I know with my '99 GTX that I could get around 20-21 mpg when it was stock. Now, it's a GTX so it had the 2.5" catback and SLP intake already. I added a 3.4" pulley, 3" DP with no cat and self tuned the PCM (HPTuners). I was seeing around 23-24 mpg when I sold it. I never changed my driving style and that was usually getting on it pretty good twice a day for the highway on ramps. 8) It was my daily driver and saw a mix of city and highway driving. I've heard that the VS cam can give you 3-5 more mpg, but that's only if you can keep your foot off of the gas pedal. Quote Link to comment Share on other sites More sharing options...
john99gtp Posted December 9, 2005 Report Share Posted December 9, 2005 well lets see here, 3.4 pulley, SLP headers, DP, diamond pistions, i forget exactly what his compression ratio is, but i know its higher then factory, 9:5:1 mabie?? mls headgaskets, a intense stage 1 cam, modified DHP pcm code, 160 drilled stat, fresh 4t65e, with better clutches all around, high stall Torque converter, setups got about 3000-4000 miles on it i've been with him in the car and when we are on a flat streatch of highway and he hasen't been goofing off it will pull off 36 or so MPG. at least according to the DIC. ive seen 36mpg, when i reset the dic going down hill. In fact, ive seen 99.9mpg, but i dont claim to have a 100mpg w-body. but thats so....unbelieveable, especially if he bumped his compression, and with a stage 1 cam, im sorry, i gotta stop before i piss my pants from laughing. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted December 9, 2005 Report Share Posted December 9, 2005 whatever, i really could care less what you think. fact is thats what i've seen the DIC display on a flat streatch of highway on a semi long trip. i honestly have nothing to gain by making that up Quote Link to comment Share on other sites More sharing options...
1BADVR4 Posted December 9, 2005 Author Report Share Posted December 9, 2005 Come on guys, the DIC is just an estimator. You've got to use the trip odometer. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted December 9, 2005 Report Share Posted December 9, 2005 i know, and thats why i have been saying "what the dic displays" if it were my own car, i could give you numbers. Quote Link to comment Share on other sites More sharing options...
sl3196 Posted December 9, 2005 Report Share Posted December 9, 2005 Ya the dic on mine is usually at least 2-3 mpg high. I did get 29mpg on the way home from a trip today though yay(actual not according do dic, it said like 32.7). Quote Link to comment Share on other sites More sharing options...
pwmin Posted December 10, 2005 Report Share Posted December 10, 2005 the 3.4 isnt going to hurt it much, the headers and dp will help, but the cam will hurt. id say it would get better mpg with that setup, but im not sure how much. if you knew what it was stock according to the dic, that would help. this is ridiculous. Quote Link to comment Share on other sites More sharing options...
93CutlassSupreme Posted December 10, 2005 Report Share Posted December 10, 2005 the 3.4 isnt going to hurt it much, the headers and dp will help, but the cam will hurt. id say it would get better mpg with that setup, but im not sure how much. if you knew what it was stock according to the dic, that would help. this is ridiculous. this thread is pretty fucking gay Quote Link to comment Share on other sites More sharing options...
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