stik6shift93

Alright I've noticed that I've been filling up the tank on my car quite often, I never paid attention before so I'm not sure if its always been like this. Anyway I decided to see what kind of mileage I could get, I put in 10 gallons and drove like i normally do(shift at about 2500-3000) I ended up getting 120 miles to the tank. I suspected it was my heavy foot that was killing my mileage so I put in 10 more gallons. I drove extremely easy shifting at about 1800rpms. This time around I only got 130 miles to the tank, I had expected a lot more like around 17-18. All my car has is boltons aside from the nitrous which I didn't use. I know that headers and intake make your car more efficient so I'd expect those might actually help my mileage, the gears are stock btw. What could be giving me such bad mileage? Could it be a leaking nitrous solenoid? Or is it just normal? Also I have subs and such in there and I realize they need more juice and require more from the alternator. Is there anyway the extra amperage needed will cause the alternator to produce more drag? Thanks for any input
Brad

Black97Z

Even in the winter doing city driving my bolt on car will get almst 20mpg. (BTW, i also have subs) Summer can be as good as 28 highway

I'd check spark problems, maybe change plugs and wires. Also, low tire pressures can give you a lot of rolling resistance and lower your mileage. Check them when they're cold and make sure the pressure is right. In the winter (at least in the NE) they have a different formula of gas. That coupled with all the extra idling (warming up, etc) tends to kill your mileage a little too. I'd check the two things I mentioned then hope for the best.

BigRich

i have a 94 Z28 M6 and got 13.7 mpg in mostly city driving before going to full exhaust.

this was very accurate as i filled the tank to the top, drove and refilled to 3/4 as i usually do, and after 1,000 miles, roughly, I filled the tank back to full and did the math. i had all the reciepts and with a calculator it's easy to get a very good average.

i'm doing another 1,000 mile test now after the hooker shorties, 3" cat, hooker cat back, new plugs and wires and O2 sensors.

i have this theory that LT1 M6 gets worse mileage than LT1 A4 because we rev more and higher to get through the gears. also, in city driving, i find myself leaving it in 4th (1.00 ratio) even when lifting off the gas, but an A4 would be in a higher gear, maybe even top gear when you lift off the throttle and coast. i think the A4s get better mileage in city driving this way.

what you guys think?

Mizz96Z28

Try the O2 sensors. Might need replacing and do a tune up if you havent recently.

Myles

stik6shift93

Plugs are less than a 1000 miles old and all the plug wires are perfect. o2s where replaced not that long ago, a tune up shouldn't really help any. Still trying to figure this one out My 97z with the same mods which was an auto with a 2800 stall pulled of 18.2 mpg in conservative city driving. I'd think that manuals would get better gas mileage, especially when compared to an auto that has a stall in it. I'm clueless, I think I'll check tomorrow to see if my fuel solenoid is leaking. Anybody else?

RobK

When I changed O2 sensors on my '94 Z28, I got an additional 50+ miles per tank after it slowly became poor.

Dr.Mudge

Skip shifting (like CAGS) will help improve MPG. A stick should get better MPG if the car is running fine, and the driver knows what they are doing.

Jeff Collop claimed 16 MPG city, and I think 26 MPG freeway, on an open loop, leaned out 390 RWHP car, so its not impossible to make good MPG with a few light mods. I know a guy getting around 10 MPG with a Hotcam, so there are those cars too. Exaust leaks or etc.

stik6shift93

Dr. mudge, when you skip shift like that into such a high gear. Does it really help you? I was thinking of doing that but realized that you end up having to give it more throttle and guessed that it wouldn't help mileage as much as if I where to go light throttle threwout all the gears. Am I wrong in thinking this? Basically I'm asking does it make a difference if your in a taller gear at heavy throttle low rpm vs a shorter gear at light throttle with a little more rpm.

jim88iroc305

replace/clean air filter
check timing
check idle speed
check tire pressure
check injectors dirty/clogged
check fuel injection system
check gas lines
check tire pressure

from what you describe it should be one of the above

I get 20+ mpg all around and average 30 mpg on open road. on open road I've gotten 400 miles to tank. I log mileage for work so I always have miles driven and gallons purchase to figure consumption.

Dr.Mudge

stik6shift93, your right somewhat, if you compensate by revving it up a bit you could use more gas, but its the constant up/down through the revs that uses gas the most, according to the EPA. These cars make enough TQ though that you dont have to rev it out that much, I'd pretty routinely shift between 1800-2200 depending on uphill/flat/how fast etc. One thing thats "nice" about FI cars though, there isn't alot of difference between having a little fun with the car, and driving like grandma, in terms of MPG.

Even in my 240Z which is not a TQ king, I shift 1/3/5 or 2/4/5 almost all the time. I gear change in that car alot faster than in the Camaro though due to the way its geared.

In the Camaro 1/3/4 for 35-40 MPH stuff was pretty common, for 50 MPH I'd end up in 5th and on the freeway 1/3/5/6 or 1/2/4/6 depending, on where I accelerate the most, sometimes I just get away from the cars behind me and then granny it from there. All kinds of possible gears to skip, does it really help that much? I dont think that much, but a little yes.

It is very wierd though that some guys claim near 30 MPG on trips and others are in the teens. Most of us on the site are buying Bosch O2s I believe right? Not cheapie Neighoff etc? Maybe there are other possibilities that I'm not seeing. Gas quality will make up some of it I'm sure, but 1-3% I'd guess, not as much as were seeing...

12sec97Z28

Yeah, that doesn't sound right. I've got 4.10s in my bolt on car, and I get 15 in the city and around 20 highway/city mixed.
When was the last time the fuel filter was changed? Ran injector cleaner through it? Air filter was cleaned or replaced? The problem I'm having right now is my EGR is bad and my cat I think is clogged up, and my mileage is down near 12, so one of those is killing my mileage too. Add that to the list of suggestions already given. Poor gas mileage is usually something as small as a filthy filter.

ryker77

Most of what you guys think about MPG is not true.. I can say this because I have put 33000 miles in my Honda Insight. Granted its a 3 cylinder 1 liter engine. It still a gas engine.

What I have found. Air pressure in your tires is a major killer in performance. The little honda has some small tires yet when they get low on air the engine has to work harder to get the tire to roll and most tires rotate 800-900 revs per mile. So each mile the engine has to overcome bad tire pressure 800-900 times. I'd say your Camaro has at least 245 width tire and that alot of rubber to overcome.

Engine RPM has very little to with MPG as compared to lugging the engine. Your engine is designed to effectivly operate at a certain RPM range. Yes at idle speed and under no load your engine uses very little gas to operate. Yet take that same engine apply 3000lb car and it will not operate efficiently at idle at 45mph or any speed. Its all about efficincy. In my honda I can get better MPG in 4th gear vice 5th at speeds less than 70mph. If I try to use 5th and the road has any incline it will require more fuel to operate. Yet in 4th I can use less fuel but higher RPMS in a more efficient matter.

I noticed that in both my honda and my supercharged Lt1 that its better to use the rpm and hp quickly and get up to speed the use the proper gear... Hence GM's skip shift. For the honda 1st gear 4500-5000rpms shift to 2 run it up to 4000-5000rpms now Im at 45-50mph and I use either 4th or 5th. For my Lt1 its 1st kinda easy or I'll spin then 2 up to 45mph then 5th. I only use 6th above 75 or if I'm driving down hill. I can watch my MPG gauge in my honda for the LT1 I watch my boost gauge.

I also use the gravity method. Down hill I'll speed up alot then barley back off the pedal as I go up a hill. Yes you may loose a few MPH yet it will save alot more gas.

Of course a tune up never hurts


Just a few tips to help out with this expensive *** gas prices. BTW you can thank Mr. Bush and his daddy for that.

KeVMaN

I get about 10mpg what tire pressure do you guys run, and how do you clean your fuel injectors (a bud said he went from 10mpg to 17 when he got his cleaned). My car kinda smells like gas too so i'm guessing that its running really rich

ryker77

Check the max tire pressure on the tire on pump it up to that. During winter you can go slightly beyond that. But never in the summer or warm weather.

I keep my honda at 48-50psi and my lt1 at 44-46.

12sec97Z28

I can't say i fully buy that story. It may have some merit and some truth, but i went from 245/45-16 street tires running good pressure to drag radials running a MAX of 25 psi every day, and i didn't have any difference in mpg.
To clean fuel injectors, you can either buy the injector cleaner stuff from any auto parts store or even wal-mart for a quick job, or you can have them serviced and cleaned by hand for more money. I personally just use the injector cleaner from the stores. Seems to work well.