poor mileage after longtubes and tune
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Joined: Oct 2006
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From: Webb City, MO...out in the garage
poor mileage after longtubes and tune not sure what the cause is here...the owner says the car is getting 13-14mpg in city driving and 21mpg with all highway driving at 70mph. it's a 2002 Z28 A4 with 18,000 miles on it, literally was a barn find. I installed longtubes and a lid along with AIR/cat delete. The car runs strong and feels fine, fuel trims are pretty good. I notice the O2s don't seem to switch real fast at idle but they do switch. I dont know if this could cause that much of a drop in MPG's though unless he just idles around town all day. i had him bring the car back and just went for a drive. i attached the log and current tune, tuning with HP Tuners. Curious what you guys might think. Thanks
There isnt much done in the tune to improve mileage. There are a bunch of little things to do that can help mileage but the tune has to be dialed in before those will help. I would start out by tuning the VE table, work on the timing tables and that will get you going in the right direction.
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I would take city driving MPGs with a grain of salt. You don't know how the guy's driving characteristics and how much stop and go/idling there is. Some days I can get 8mpg and other days I can get 17mpg all on the same stretch of city driving all depending on how many lights I catch or how hard I drive or how early (if at all) I start coasting to stops.
Highway driving doesn't seem that bad, and he has to realize it will get a little less with all those mods. If the tune is good and there are no leaks (air or exhaust) then I would tell hem that's the cost of playing this game.
Highway driving doesn't seem that bad, and he has to realize it will get a little less with all those mods. If the tune is good and there are no leaks (air or exhaust) then I would tell hem that's the cost of playing this game.
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Joined: Oct 2006
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From: Webb City, MO...out in the garage
There isnt much done in the tune to improve mileage. There are a bunch of little things to do that can help mileage but the tune has to be dialed in before those will help. I would start out by tuning the VE table, work on the timing tables and that will get you going in the right direction.
Thread Starter
Joined: Oct 2006
Posts: 2,608
Likes: 0
From: Webb City, MO...out in the garage
I would take city driving MPGs with a grain of salt. You don't know how the guy's driving characteristics and how much stop and go/idling there is. Some days I can get 8mpg and other days I can get 17mpg all on the same stretch of city driving all depending on how many lights I catch or how hard I drive or how early (if at all) I start coasting to stops.
Highway driving doesn't seem that bad, and he has to realize it will get a little less with all those mods. If the tune is good and there are no leaks (air or exhaust) then I would tell hem that's the cost of playing this game.
Highway driving doesn't seem that bad, and he has to realize it will get a little less with all those mods. If the tune is good and there are no leaks (air or exhaust) then I would tell hem that's the cost of playing this game.
Thread Starter
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From: Webb City, MO...out in the garage
How do I go about dialing in spark advance without a dyno? MAF is spot on in OL, fuel trims in CL can't get a whole lot better...I don't have much time for this car right now as I'm very busy, just trying to help the guy out. What about the 2.73 gears? Won't those hurt in mostly city driving?
I have a 22/224 .629/.629 cam in my G8 and get 18-20-mpg in town and 24-26mpg depending on the speed limit since we have alot roads with 75mph limits so everyone drives 80mph.
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From: Webb City, MO...out in the garage
There isnt an easy way, it takes time and experience. The maf is only part of fueling, dial in the VE also. Without spending some time on the tune its not going to get better mileage, there isnt a single quick fix or simple single table change and its going to get better mileage. There are alot of small things to change in the tune that add up and can help mileage.
FWIW, my M6 SS got 20/28 with a 231/237 cam and 4.10s....now it gets 10/20 with the 454, still M6 with 4.10s at 600rwhp on 91....this Z28 should get 15mpg+ in my mind.
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From: From Ohio now in that state up north
May be a real issue but any time I hear exhaust and poor millage I think the guy has his foot in it loving his new sound but that isn't always the case.
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From: Webb City, MO...out in the garage
95% of the time I'd say you're correct. This guy babies this car to the point it's actually irritating to ride in it with him.
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From: From Ohio now in that state up north
What did he get before the install? How is he calculating his city and highway mpg is he actually going through full tanks of gas only city and only highway driving?
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From: Webb City, MO...out in the garage
He took a couple road trips for work that were 100% interstate driving from full to empty and averaged 21mpg. I believe he said it got 23 or so before. He's notice his range has dropped in mixed driving from somewhere over 300 miles to well under 300. He lives in town and works in town, so he's basically driving all city and went through 3 tanks of 13mpg before calling me. I don't know exactly how the guy is calculating it but I assure you he's no idiot and i trust his figures to be accurate. I suspect the 2.73 gears are a good part of the problem. I dialed the VE error in closer to 0, although it wasn't off by much at all...not sure what else to do other than ride around with him for a week everywhere he goes logging every second of it....but that isn't happening, lol.