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'99 Z28 - Slight Fuel Mileage Increase?
04-16-2013, 04:46 PM
#1
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'99 Z28 - Slight Fuel Mileage Increase? I daily drive a '99 Z28 M6 with approximately 260K miles on it. Original LS1 and trans. I'm on my third clutch and I've rebuilt the front and rear suspensions. Original fuel pump.
My daily commute is 58 miles each way, so 116 miles round trip. For the most part, this is all four lane driving, cruising at 63 mph average. I travel from eastern West Virginia into Northern Virginia, so the terrain would be rolling hills.
I've documented virtually every tank of gas (plus it's associated mileage) for the last 10 years in this car. So when I say that I average 26 mpg, it's documented and not a guess.
Two weekends ago, I changed oil and trans fluid, and popped in a new fuel filter. Probably 80 or 90K miles on that old filter. I'm on my 5th tank of gas since then and I've averaged 28.5 mpg over those 5 tanks.
Why? I get that the pump is now working against less restriction, and I do sense a slight increase in acceleration. But why would my gas mileage increase like that? That's a 9% increase! Any insights from the motor guys out there?
At first I thought that it was due to a change in gas additives at the pump associated with the change from winter to spring, but I don't have any corresponding deltas from any other years.
Thanks
My daily commute is 58 miles each way, so 116 miles round trip. For the most part, this is all four lane driving, cruising at 63 mph average. I travel from eastern West Virginia into Northern Virginia, so the terrain would be rolling hills.
I've documented virtually every tank of gas (plus it's associated mileage) for the last 10 years in this car. So when I say that I average 26 mpg, it's documented and not a guess.
Two weekends ago, I changed oil and trans fluid, and popped in a new fuel filter. Probably 80 or 90K miles on that old filter. I'm on my 5th tank of gas since then and I've averaged 28.5 mpg over those 5 tanks.
Why? I get that the pump is now working against less restriction, and I do sense a slight increase in acceleration. But why would my gas mileage increase like that? That's a 9% increase! Any insights from the motor guys out there?
At first I thought that it was due to a change in gas additives at the pump associated with the change from winter to spring, but I don't have any corresponding deltas from any other years.
Thanks
04-17-2013, 10:43 AM
#2
If your fuel pressure is now higher, you could be getting better performance out of your injectors and getting better combustion. I'd bet that the temperatures and switch of gas formulas are also helping.
On my car, I can see a 4 mpg difference at the gas pedal. If I go 55-60, I've gotten up to 29.5 mpg. If I average 75, I drop down below 26. Is there any road construction along your journey that might be helping, also?
On my car, I can see a 4 mpg difference at the gas pedal. If I go 55-60, I've gotten up to 29.5 mpg. If I average 75, I drop down below 26. Is there any road construction along your journey that might be helping, also?
04-17-2013, 10:58 AM
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It could be the difference in fuel pressure, I guess. I should have thought ahead and bought a fuel pressure gauge to test prior to swapping the filter. I need to have the injectors cleaned and also to swap out the pump. It would have been good to baseline the fuel pressure and then capture the changes along the way.
My commute has been pretty much constant over the past 10 years. Slightly shorter at times, but generally the same route. 29.5 mpg is awesome ....
As an aside, I drove our 2011 Civic automatic for a week and averaged 33 mpg. And then I took our 2010 Honda CRV AWD on a longer trip over the weekend, and average 43 mpg. Both are nice cars, but I prefer my Z28.
My commute has been pretty much constant over the past 10 years. Slightly shorter at times, but generally the same route. 29.5 mpg is awesome ....
As an aside, I drove our 2011 Civic automatic for a week and averaged 33 mpg. And then I took our 2010 Honda CRV AWD on a longer trip over the weekend, and average 43 mpg. Both are nice cars, but I prefer my Z28.
