Horrible Gas Milage!

[mexellent]

I've got a 1998 VW Jetta GL with the 2.0 liter engine. And Im getting HORRIBLE gas milage. I've done a couple of performance modifications such as an intake, exhaust, and cam, but after I did those, I used to be able to get at least 24 MPG city. Now i get 22 MPG all city. Whats going on here?

[kickflipjr]

Performance modifications do not help fuel economy under normal conditions. They might even hurt fuel economy. The performance exaust is no benifit at low rpm.

[DracoFelis]

Originally Posted by mexellent

Whats going on here?

There are many factors that can influence FE (fuel economy), and (without more info) we really can't tell which may be the cause in your case. However, the first thing I would suggest, it to check the FE basics. For example:

Tire pressure? Now that it's getting colder, tire pressure will naturally go down (unless you put more air in the tires to keep them at summer pressure). And lower tire pressure can cause your FE to tank! Which is why when it gets colder, you should check your (cold) tire pressure more often, and top off the air in the tires as needed.

What about oil changes, or other maintenance (including replacing air filters, cleaning your fuel injectors, etc)? If some needed maintenance is not up to date, FE can suffer.

Are you using different gas (different brand, or different octane rating) than you used in the past? Differences in gas frequently account for "unexplained" differences in FE.

What about driving conditions? Bad weather can lower FE.

Are you driving any differently? 2 mpg can easily be explained by simply having a little more of a "lead foot" than normal. And it can equally be explained by having to idle longer (caught in traffic, for example).

Are you using a different engine oil? I find that there really are FE differences (not to mention performance/power differences) between oils. I personally use a 5w30 full synthetic, and I get much better results than I did using a cheap dino oil. Oh yeah, don't forget to check the dipstick from time to time (in my wife's Civic, the FE really tanks when she lets the oil level get low)...

Are you overdue to replace your transmission fluid? Keeping clean "high quality" transmission fluid in your transmission, can make a little difference in FE (not to mention extending the life of the transmission).

Are you using more electricity (lights on more, for example) than you previously did? Many people assume that car electrical power is "free", when really the more power you get from the alternator the more drag the alternator puts on the engine (and therefore the more electricity you use in your car, the lower your FE will be, as that electricity takes some extra gas to produce). Which is why I have most of my car converted over to energy efficient LEDs (instead of the power sucking incandescent bulbs it came with), and also avoid using the (high energy using) headlights when they are not needed. But now that we are getting later in the year, the power sucking accessories (including the car lights) become more needed, and this can lower FE some.



And those are just factors "off the top of my head", I'm sure that list isn't even close to being complete. If you read the posts in this forum, you will see that many things can influence FE. So without knowing your car (or how you drive it), we can't really tell you what happened to lower your FE. But we can point you to things to look at that effect FE. And some of these tips would likely help your FE (possibly even giving you more MPG than you started with), even if you never find out why your current FE took a dip...

[rh77]

First, welcome to GasSavers!

I'd review the FAQ section and take DracoFelis' advice.

It sounds like you made performance mods instead of economy mods (like a cold-air intake may be worse than a hot-air intake, for example).

We're here to answer specific questions if you have them.

The best way is to track mileage by using the GasLog here, and to get a feedback device like the ScanGauge to train your driving style.

Good luck...

RH77

[FormulaTwo]

Could be your driving style has changed.
You may not even notice it. I know when i had exhaust/intake etc.... I became more used to shifting based on the sounds i was hearing.
Pay more attention to the rpms you shift at.
With that setup your engine will be passing more air, throughout the rpm range.
You may have to shift lower to compensate.

[mexellent]

thanks guys. Ill be sure and fix all those things. Ive got the stock cam. I might just stick that in later.

[onegammyleg]

Hi FormulaTwo

I agree with you ..

The difference was only 10% and that could easily be from a changed driving style - and higher shift RPMs etc.
And a car that starts at 24 isnt really that good anyway , a drop to 22 iant going to make much difference.

[kickflipjr]

Originally Posted by theclencher

Careful...

Some mods do help performance and FE and some don't.

Yeah thats true.

[BEN_EJ8]

Originally Posted by theclencher

Careful...

Some mods do help performance and FE and some don't.

Back in my Uncle Ben days, I had a CAI and catback exhaust on my Integra. EPA was 25/31, I used to average 30 all city, driving like a typical impatient lead footed teenager. I still cant believe I once got 35 for the tank all city, but changing out my spark plugs, which were white tipped, gave me a good idea why I was getting the FE I was.

[rh77]

Originally Posted by BEN_EJ8

Back in my Uncle Ben days, I had a CAI and catback exhaust on my Integra. EPA was 25/31, I used to average 30 all city, driving like a typical impatient lead footed teenager. I still cant believe I once got 35 for the tank all city, but changing out my spark plugs, which were white tipped, gave me a good idea why I was getting the FE I was.

Holy crap! What year/trim was the Integra? Also, was it a manual? I'm struggling to average 31 with all kinds of techniques and mods.

[ketel0ne]

Your Jetta is rated right in the 22-24mpg range for city.


Volkswagen Jetta
4 cyl, 2.0 L, Man(5), Regular 24 31

26 combined

Volkswagen Jetta
4 cyl, 2.0 L, Auto(4), Regular 22 29

24 combined

[BEN_EJ8]

Originally Posted by rh77

Holy crap! What year/trim was the Integra? Also, was it a manual? I'm struggling to average 31 with all kinds of techniques and mods.

It was a 92 coupe GS 5 speed pig with every option, and constanty 100+ pounds of college books and tools in the back. It was probably running pretty lean, judging by the spark plugs. One time while driving 275 miles from my grandfathers last summer I filled up with non reformulated gas up in his town. I drove 75 mph all the way home, and got 38 mpg on that highway trip, 1 better than my mom did in her 04 civic, this was before I started even trying to change my driving to get better mpg; I guess you could say that car was a freak. If I drove that car like I drive my civic now, I would say averaging 33-35 mpg city would be very attainable.

[rh77]

Originally Posted by BEN_EJ8

It was a 92 coupe GS 5 speed pig with every option, and constanty 100+ pounds of college books and tools in the back... I would say averaging 33-35 mpg city would be very attainable.

Damn that Automatic Transmission! They both have the B18b1 engine and I have the options too, but geez. I was averaging 26mpg in a similar situation before I started FE mods. I can't seem to crack 32-33 for a tank with most hypermiling techniques!

I need to re-think a few things. (grumble)...

RH77

[BEN_EJ8]

If you can find a cheap hydro LS tranny I would say swap that in. I dont know how much those go for, but the old cable trannies are pretty cheap; probably because the 3rd gear synchros are bad in about 98% of them

[mexellent]

Well, I know the thread has been dead for a while, but the other day I squeezed 24.9 mpg's out of it. Ive raised the tire pressures 4psi all around and im going to try coasting some too for this next tank. I think I drive almost all city, so in retrospect, maybe 22 isnt so bad. Are hypermilers people who get 20% above EPA rating? Id have to get 31 mpg to be a hypermiler. I only got 30mpg once (400 miles out of one tank), and that was all highway @ 80mph with a fully loaded car. I dont think i can be done...

Not to fear though, I ordered a Honda Fit on July 3. Base model with a manual tranny. That should get much better milage!

[SVOboy]

to the Fit.

And I'm sure you can do the hypermiling thing, just give it some practice and you'll get there.

[Coyote X]

If you go back to the stock cam you will probably pick up some mileage. Most cams kill city mileage. My Camaro's mileage got cut in half with a cam swap and no matter how easy I drive it I can't get it up to 10mpg anymore where it used to get 25mpg driving it pretty hard.

I would say if the power increase from the cam isn't that important to you then go back to the stock cam and send that aftermarket cam in to be ground down to lower lift and duration than the stock cam and that should easily get you 5mpg over stock.

[mexellent]

At the time I wasnt concerned with FE at all, so nothing.

[diamondlarry]

Well, it just goes to show that we all start at different places in the FE game. The fact that you are here is a good first step. The numbers themselves aren't all that important. Improvement is what matters most. Welcome! Fornow, just shoot for 30 then go on from there. Little steps.

[SVOboy]

Originally Posted by diamondlarry

. The numbers themselves aren't all that important. Improvement is what matters most.

This is a dangerous thing to say. Unless you think FE is completely a game and the environment/economy/urban sprawl, waste, blah blah are not factors in anything.

[diamondlarry]

Originally Posted by SVOboy

This is a dangerous thing to say. Unless you think FE is completely a game and the environment/economy/urban sprawl, waste, blah blah are not factors in anything.

That wasn't my intent. I was just pointing out that we all start somewhere. Let's say that somebody had a car identical to mine and they only got 25 mpg when they started to be concerned about FE. They would look at my 53+ mpg and get discouraged if they couldn't get that high on thier first tank and may very well give up. I really shouldn't have referred to FE as a "game." It was a poor choice of words.

[diamondlarry]

Originally Posted by theclencher

The numbers are important.

If I started at 13 and went to 19, that's a 46% improvement, yet it still sux and is unacceptable.

Exactly. If you started at 13 and ended up in pretty much the same place, then you would know that, since there was no improvement, you did something wrong. For me, it would be more incentive to try harder.
Edit: For me, if i went from 48 up to 50 that would only be a 1.04% improvement. The next time I would expect something over 50. Staying at 50 or even declining would be unacceptable to me.

[diamondlarry]

My grandpa always used to get me to take his vehicle if we would go somewhere. I usually declined because my cars got better mileage. Sure, I could probably get better than most people in his vehicle, but mine was ultimately better for the environment.

[mexellent]

Well, I used to have a "holy airbox" (airbox with a bunch of holes in it). But I took that off today and I put an airbox with no holes back in and hooked up all the emissions stuff. I may have changed too many variables, but I figured the stock airbox with no holes is going to be better.

[Compaq888]

I replaced the hose in my old car. It had a hole but I sealed it up. The hose wasn't smooth anymore. After i put a new hose there was much better throttle response in the low end.

I started out with 24mpg and ended up with 31mpg. Sold it.

Bought a 34mpg car and now I'm at 40mpg.

[kickflipjr]

I got 24mpg on the first tank on my gaslog I figured that was ok because I was getting 28mpg in my old saturn sl1. As I learned more my mpg climbed (well, slowly climbed).

[mexellent]

WOO HOO!!! I just got 29.64 mpg out of my last tank! That was with some very basic FE techniques. I put in the clutch instead of letting the car motor. I also did the "jack rabbit" technique (accelerate "hard" on 1-3 and then shift into 5th). I also bumped the pressure on the tires by 4psi all around (36 psi).

Im very optimistic, seeing as how the car is equipped with a high performance cam and a bike rack. I can put the stock cam back in and I can also remove the bike rack. In addition to that, Ive also ordered a scan guage II. Who knows, I might just be able to make it into the 500 mile club!

=D

[diamondlarry]

Originally Posted by mexellent

Who knows, I might just be able to make it into the 500 mile club!

=D

I'm not sure how big your tank is, but 500 miles should be well within reach with your planned mods.