19 mpg!!! What should I do?

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NewToVibe
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Joined: Mon Nov 19, 2018 2:57 am

19 mpg!!! What should I do?

Post by NewToVibe »

I have a 2005 6 speed manual Vibe GT, it has around 85k miles on it, and I’ve had it for about four or five months now and has always gotten poor gas mileage. I’m not sure what to do. Please, any advice is much appreciated. Thanks.
andrewclaus
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Re: 19 mpg!!! What should I do?

Post by andrewclaus »

Where do you live, and is ethanol added to your fuel in the winter? Have you tried different gas?

Do you drive in defrost mode? If so, the A/C is on, adding load to the engine.

Have you done a tune-up? Replace plugs and PCV valve, clean the MAF sensor.

Try some fuel injector cleaner additive.

Check tire inflation, increase if needed. Check alignment.

Check for brake drag, or other drive line problems.

Look for driving tips to improve efficiency, if needed.
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vibrologist
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Location: Iowa

Re: 19 mpg!!! What should I do?

Post by vibrologist »

Let's first look at the driving conditions:
What is your method of calculating fuel consumption?
Is it cold where you live?
Do you drive short distances and the engine hardly ever reaches operating temps?
You rev the engine to which level when you go through the gears?
Do you have unnecessary weight in the car?

Now technical stuff:
Do the brakes drag?
What is the state of the plugs and air filter?
Is a CEL on?

In general folks have high expectation in fuel economy for their Vibes. After all they are econo boxes. However they are rather heavy, have high airodynamic resistance because they are high and short and they are hampered by emissions regulations.
Vibrologist
'05 Vibe

"It is important to know the difference between 'accurate' and 'precise' even if you are neither!"

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Caretaker

Re: 19 mpg!!! What should I do?

Post by Caretaker »

The only thing we really need to ask given this "much" information is:

Q. How much money have you got to spend?

A: If lots, go buy a used Prius V. They get upwards of 50 mpg and there are lots out there to choose from. Amazing reliability.
A: If little, go buy a used Honda Fit. They get 32 mpg, are amazingly versatile and are even more reliable than the Prius V which is hard to do.
SeattleJeremy
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Re: 19 mpg!!! What should I do?

Post by SeattleJeremy »

Did you ever get your "Lack of acceleration" issue figured out?
viewtopic.php?f=17&t=46789

Sounds like the car still needs a tune up, brakes inspected, or maybe a clutch. Have you had a mechanic inspect the car?
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jolt
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Re: 19 mpg!!! What should I do?

Post by jolt »

Little information here to go by so little answers is what you get.

p.s. A bad or slipping clutch will produce horrible gas mileage. Also when and how you shift the transmission will greatly impact the gas mileage.
NewToVibe
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Re: 19 mpg!!! What should I do?

Post by NewToVibe »

Hey there guys sorry about the lack of response, incredibly busy. But my 19 mpg issues are fixed. And so is the lack of acceleration. Turned out my clutch was going however when they replaced it they never tightened the air flow back to the throttle body (something I, at the time had no clue to check) so after that was tightened it got around 25 mpg. I then replaced the plugs, minor scorch marks on the ceramic, the pins were corroded though. I flushed the engine with liqui-moly and changed out the oils. When I was changing the transmission fluid out I couldn’t tell for sure but the fluid that came out was looking like atf. I put redline in it and it’s now getting closer to 28-30 mpg.
As far as my daily driving goes, I live in the Pacific Northwest and drive from Longview, wa to Portland, or 5 days a week. A little less than 100 miles a day. I let the engine get up to temp before I drive. Usually all the way not just until it gets to proper idle speed. I only use premium in the engine. I’ll use medium grade only when I have to.
As far as my shifting, I usually rev to about 2.8 to 3 rpm before I engage the shift. But I’m worried that this car isn’t pulling enough for being a six speed. For example going 80 mph the car is revving at 3.5 rpm in sixth gear. I asked a mechanic about this and he said that since the tires are so small it makes perfect sense... I just feel it makes sense for a five speed not a six??? Does anybody have thoughts on that?
SeattleJeremy
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Re: 19 mpg!!! What should I do?

Post by SeattleJeremy »

You're kinda all over the place so I'll break up your post, and try to answer the highlights.
NewToVibe wrote: Fri Apr 05, 2019 7:31 amit’s now getting closer to 28-30 mpg.
This is what this car should be getting. Great!
NewToVibe wrote: Fri Apr 05, 2019 7:31 amUsually all the way not just until it gets to proper idle speed.
There is no need for this. Start the car, and drive it. Stay below 5000rpm until the water temperature reaches the normal range.
NewToVibe wrote: Fri Apr 05, 2019 7:31 amI only use premium in the engine.
Good only use Premium. If you put in Mid-grade, do not go above 5000rpm.
NewToVibe wrote: Fri Apr 05, 2019 7:31 amBut I’m worried that this car isn’t pulling enough for being a six speed.
When the 2ZZ is below Lift, it's not going to pull very hard. It's just the nature of the engine. When it changes over to the Lift cam profile around 6000rpm you should feel and hear the change.
NewToVibe wrote: Fri Apr 05, 2019 7:31 amFor example going 80 mph the car is revving at 3.5 rpm in sixth gear.
6th gear is for cruising on the highway and fuel economy. Pressing the accelerator at 3500rpm isn't going to do much because of the gearing. If you need to accelerate faster at 80+mpg, then you need to downshift.
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zbyers
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Re: 19 mpg!!! What should I do?

Post by zbyers »

SeattleJeremy wrote: Fri Apr 05, 2019 9:24 amYou're kinda all over the place so I'll break up your post, and try to answer the highlights.
I read the post, then went to type up a response and saw you did. SeattleJeremy hit the nail on the head with his response. Hopefully that's the info you were looking for NewToVibe.

You can also follow the links in my signature for lots of info about the vibes throughout the site, especially the "Everything You Need To Know" thread.
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NewToVibe
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Re: 19 mpg!!! What should I do?

Post by NewToVibe »

Hey so thank you for responding and breaking up my post, it was helpful to even me. I appreciate the feedback and feel a lot better about the car overall. To be honest I really don’t think I want to get rid of it. It’s such an awesome little machine! And now that I have it to where it should be, does anyone here know anything about upgrading to a cool air intake system or headers for the vibe? I’m having trouble finding things that seem compatible.
zbyers
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Re: 19 mpg!!! What should I do?

Post by zbyers »

TBH, you're not going to gain anything from just headers or a CAI. As I always tell people, a CAI or SRI make my grandma car sound like her chihuahua when I come over :lol:

But to answer your question, DC Sports makes a header for the Vibe/Matrix. Pay attention to the difference between AWD and FWD as they have different exhaust layouts. and CosmoRacing is probably your best bet for a CAI/SRI.
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SeattleJeremy
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Re: 19 mpg!!! What should I do?

Post by SeattleJeremy »

I agree with zbyers, adding more parts will make it louder, but not much faster. Many performance parts for the 2ZZ engine are made to increase the engines numbers on a dyno or it's abilities when in Lift (Toyota's version of vtec). So things like exhaust and intake will help when at the top of the RPM band, but may hurt performance lower at normal driving speeds.

When looking for exhaust parts make sure to get the one for the Vibe GT/Matrix XRS. The Celica GTS exhaust parts are different (I think the intake is different too).
One really good resource for Matrix XRS/Vibe GT (2ZZ) parts is https://www.monkeywrenchracing.com
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joatmon
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Re: 19 mpg!!! What should I do?

Post by joatmon »

NewToVibe wrote: Fri Apr 05, 2019 7:31 am. For example going 80 mph the car is revving at 3.5 rpm in sixth gear. I asked a mechanic about this and he said that since the tires are so small it makes perfect sense... I just feel it makes sense for a five speed not a six??? Does anybody have thoughts on that?
tldr summary:
80 mph at 3500 is about right for a GT. see below if not avoiding math
I think the # of gears and gear ratios in the 6th speed were designed to allow upshifting near redline and staying in lift




In a manual transmission car with no clutch slipping, or an auto with the torque converter locked up there is a direct mechanical connection between the engine and the tires. The speed the tires spin depends on the engine RPMs, the overall gear ratio and the tire diameter.

The relationship between RPMs and miles per hour depends on transmission, gear selected, and tire size.

For the 1st gen Vibes (03-08) there were 4 transmission options: Base 5 speed manual, GT 6 speed manual, base 4 speed auto, AWD four speed auto. The gear ratios for these are

Manual 6 speed
1st : 3.17
2nd : 2.05
3rd : 1.48
4th : 1.17
5th : 0.92 (overdrive)
6th : 0.73 (overdrive)
Reverse : 3.25
Final Drive Ratio: 4.53

Manual 5 Speed:
1st : 3.17
2nd : 1.90
3rd : 1.31
4th : 0.89 (overdrive)
5th : 0.73 (overdrive)
Reverse : 3.25
Final Drive Ratio: 3.94

Auto (FWD):
1st : 4.01
2nd : 2.21
3rd : 1.43
4th : 0.98 (overdrive)
Reverse : 3.27
Final Drive Ratio: 2.96

Auto (AWD)1st : 2.85
2nd : 1.5
53rd : 1.00
4th : 0.70 (overdrive)
Reverse : 2.34
Final Drive Ratio: 4.24

In this case, the gear ratio means the ratio of speed between the input and output. A gear ratio of 2 means the input spins twice as fast as the output. After the selected gear ratio, the transaxle has a final drive ratio that works the same way. If the gear ratio was 2, and the final drive ratio was 3, the engine will spin 6 times faster than the axle.

After that, you need to factor in the tire circumference (or pi * tire diameter), and throw in a unit conversions of 60 minutes/hour and 1 mile/63,360 inches to get from engine RPMs to vehicle MPH

from a calculator at https://tiresize.com/calculator/ the standard tire diameters are
205/55R16 - 24.9"
215/50R17 - 25.5"

putting this all together using the most common 205/55R16 tires
Engine RPM / gear ratio /final drive ratio * wheel diameter in inches * pi *60 min/hr *(1mile/63,360 inch) = miles per hour
To simplfy this
RPM /gear/final drive * (24.9*3.1416*60/63,360)
or RPM/gear/final * 0.07408
using the most common 205/55R16 tires

With all that, a GT at 3500 RPM in 6th gear should be moving at 3500/0.73/4.53*0.07408 or 78.4 mph, close enough to the 80 you observed

A side note, since the early 5 speeds had reliability issues, some have swapped in the 6 speed, but given the difference in final drive ratios,
for the same speeds in top gear, the 6 speed car will be running about 15% higher rpm than the 5 speed (4.53/3.94)
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