Volkswagen Passat Forum banner
1 - 20 of 52 Posts

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #1 · (Edited)
Guys,

Let me begin by apologizing for the long post.

Some of you have been following my saga of trying to track down why my fuel economy is lower than it used to be, but yet the MFA records about what I used to get before this problem began.

My Car: 2003 1.8T variant, with Tip, 43,000 miles on the clock. Oil has always been full synth, currently M1 0w-40. Tire pressure set, as always, at 32 PSI all around - checked religiously. Tires were exactly the same before and after this decrease was noted (Nokian WP All Weathers). Fuel Quality: Only 93 octane, but I have tried different stations and pumps without success. I fill the tank on the slowest automatic fill rate, and do not top off. Air filter: OEM paper style - I have never used a K&N filter. Driving Style: Grandma. None of these items changed during the onset of this problem.

Let me summarize the past: In February, while filling the tank, the nozzle did not automatically shut off, overfilled my tank, and spewed about 1/2 a gallon of gasoline on the ground. Since then, my fuel economy has been lower than it previously was even on repeated, well-documented, easy trips.

I found a fuel leak near my fuel filter. Changed out the filter and repaired the leak. No significant change in fuel economy.

Air filter changed and slush screen cleaned repeatedly. No change noted.

Sparkplugs only had 20,000 miles on them, but I changed them out with OEM NGKs, properly gapped. No change noted.

I had the dealer scan for codes - they found nothing. All settings were reset to basic, with no change noted.

Since the onset, about two months later, I did get MIL code for the air intake temperature sensor. I cleaned the sensor (it was a bit oily) with spray brake cleaner, cleared the code, and no other MILs since. Dealer tells me that the sensor is not showing a code and that the sensor is either good or bad, doesn't show a gradual degradation.

I had some oily seepage around the fuel injectors. I replaced the o-ring seals. No change in my economy with the change.

I have examined the entire visible length of the fuel lines and see no leaks and smell no fuel anywhere. I paid specific attention to the fuel line under the hood, at the firewall. Everything looks good.

I made a trip over the weekend to Erie, PA from Pittsburgh. This is an easy run, on gentle terrain that typically nets about 32 mpg. I set the cruise at 70 mph and off we go. Not much traffic, and I never had to go off cruise. My MFA showed about 31 MPG, but a hand calculation showed 28 MPG. This is really depressing me.

I have graphed out different variables to try and track this down. At present, the best correlation seems to exist between how many hours the engine has run, and the discrepancy between the MFA and a hand calculation for mileage. I'll post that graph later - it's on a different PC. On a long run time, I'm missing almost 1 gallon of fuel!

What am I missing?? The fact that there is a correlation between engine run hours and mileage discrepancy would seem to say that I'm leaking/losing gasoline while running. Yet I see and smell no evidence of leaks anywhere. I'm beginning to suspect a EVAP problem - but I'm not that familiar with system and don't know where to begin. Does the tank vent at all? Are there check valves that I should be looking at? Can the engine consume fuel from the tank, without it going through the measuring process of the MFA via the injectors?

I'm also thinking of buying a VAGcom, but I'd need suggestions/guidance on what to look for within the car's systems once I had it. Bear in mind that the dealer found no codes when they checked this after about two months into this problem.

I'm thinking about changing out the air intake temperature sensor, since that's the only code I've every had on this car in almost five years of ownership.

This is truly pissing me off - I'm not seeing the fuel economy that I previously had, despite the MFA recording about the same as pre-problem under similar driving styles and trips. 28 MPG as my top fuel efficiency is just not acceptable, given my driving style.
 

·
Self inflicted facepalm
Joined
·
1,445 Posts
28 is pretty stellar for this thing. I'd say you are in the market for a different car/scooter.

Your biggest barrier now is the weight.
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #3 ·
28 is pretty stellar for this thing. I'd say you are in the market for a different car/scooter.

Your biggest barrier now is the weight.
34 was my previous recorded high mpg - that's stellar. 28 is what I would expect from the v6. :(
 

·
Registered
20 GTI S
Joined
·
888 Posts
I made a trip over the weekend to Erie, PA from Pittsburgh. This is an easy run, on gentle terrain that typically nets about 32 mpg. I set the cruise at 70 mph and off we go. Not much traffic, and I never had to go off cruise. My MFA showed about 31 MPG, but a hand calculation showed 28 MPG. This is really depressing me.
This trip you took; did you run the A/C the whole time? If so, 28 is about as good as you're going to get going 70 on the interstate. I'm sure you know this, but gas mileage drops dramatically one you start going past 55-60 mph. Plus the auto trans, and the increased weight of the Variant over the sedan, it sounds like you're getting almost as much out of a gallon as you should.

Just for comparison's sake, my wife's car (02 1.8t Tip)averages 31 mpg on long trips doing 55, and around 28-29 doing 70 on the interstate with A/C on.


Mike
 

·
Registered
Joined
·
853 Posts
It's a long shot but you might check the differential / transmission fluid just to be sure you're not low.
 

·
Registered
Joined
·
830 Posts
:) Yeah, I have a thread going re: gas mileage too.
1/2 a tank = 100 miles. And that's on a manual 5spd 1.8t.
no Aircon, no heated mirrors or heated rear windows, no roof rack, fan on low-mid and windows up. I put some air in tyres today, they were a little low.
Am going to change injector seals they are a bit leaky, Put in some slick 50 fuel system cleaner today as well. After that, will do the seals maybe slick 50 is a bit corrosive.
Do you think your driving style has changed? maybe your speed is wandering up and down according to pedal pressure?
For best gas mileage I used to find freezing the accelerator was best for eco,
let the car change speed (within reason) depending on hills.

I think the v6 are more economical! :)
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #7 ·
This trip you took; did you run the A/C the whole time? If so, 28 is about as good as you're going to get going 70 on the interstate. I'm sure you know this, but gas mileage drops dramatically one you start going past 55-60 mph. Plus the auto trans, and the increased weight of the Variant over the sedan, it sounds like you're getting almost as much out of a gallon as you should.

Just for comparison's sake, my wife's car (02 1.8t Tip)averages 31 mpg on long trips doing 55, and around 28-29 doing 70 on the interstate with A/C on.


Mike
Thanks for your note. Yes, the A/C was on the entire time. My trip comparisons were taken over the entire time I've owned this car. We make trips to Erie every summer. Same passenger and luggage load, same speed, same road, same weather and A/C operations. I can show you the past records, if anyone feels that's necessary.
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #8 ·
It's a long shot but you might check the differential / transmission fluid just to be sure you're not low.
Not showing any seepage/leakage in the area. I don't think I can get the car level enough to check this in my driveway - I'll have to read up on this. Thanks for the suggestion.
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #9 ·
Do you think your driving style has changed? maybe your speed is wandering up and down according to pedal pressure?
For best gas mileage I used to find freezing the accelerator was best for eco,
let the car change speed (within reason) depending on hills.
I've typically got my kid in the car so I'm pretty conservative driver. "Grandma" style. If anything, I'm driving even more conservatively to try and save gas. I've used cruise control with very good results - traffic won't let me lock the pedal and let the speed vary.

You can see my injector seal leaks here: http://www.passatworld.com/forums/showthread.php?t=241442. Easy job to change 'em out. I never smelled fuel around them, though.

Part # is 035-906-149-A , at least on this side of the Atlantic.
 

·
Registered
Joined
·
69 Posts
My guess is the difference in ambient tempertures. Here in Atlanta I will get around 30mpg on my way to work when the temps are cooler. (28 if I use the A/C) I get 20-24mpg on the way home always with the A.C on this time of year. I sit in a little more trafic on the way home too. When fall comes back around I bet your milage will go back up.
 

·
Registered
Joined
·
130 Posts
My car('00 1.8T Variant) has also experienced a drop in mileage. Roughly 2-3 mpg less than it was 4 months ago. Checked evrything I could, changed air filter, etc. My conclusion is: It's the fuel. In the past I've made charts of fuel economy vs. where I bought gas. The differential was truly amazing, I mean like from 25 mpg to 15 mpg. This was a 1978 Chev Malibu with a 305 V-8 Auto and NOT babied at all.
The Passat was averaging 28-30 mpg, now is at 24-26, no changes mechanically, although an oil change will be due in 1K miles.
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #12 ·
My guess is the difference in ambient tempertures. Here in Atlanta I will get around 30mpg on my way to work when the temps are cooler. (28 if I use the A/C) I get 20-24mpg on the way home always with the A.C on this time of year. I sit in a little more trafic on the way home too. When fall comes back around I bet your milage will go back up.
I thought of that - but this has been happening since February - similar trips showed the same reduction in mileage, even before the weather warmed significantly (i.e., before A/C season).
 

·
Registered
Joined
·
648 Posts
This trip you took; did you run the A/C the whole time? If so, 28 is about as good as you're going to get going 70 on the interstate. I'm sure you know this, but gas mileage drops dramatically one you start going past 55-60 mph. Plus the auto trans, and the increased weight of the Variant over the sedan, it sounds like you're getting almost as much out of a gallon as you should.

Just for comparison's sake, my wife's car (02 1.8t Tip)averages 31 mpg on long trips doing 55, and around 28-29 doing 70 on the interstate with A/C on.


Mike
I'm with mike and some of the others here. 28 MPG at 70 MPH is pretty good unless you're on completely flat territory. I certainly wouldn't call it depressed.

My vote is for the fuel itself. When did the stations around you stop carrying gas w/ MBTE and start using the ethanol blend? Less energy in ethanol.



I want my..... I want my MTBE...... (or was that MTV)
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #15 ·
Question: did they introduce ethanol in your gas in feb?
Because if so, I know what it is.
To my knowledge, ethanol has been in our fuel for quite awhile, at least a couple of years, longer than the onset of this issue.

But let me ask you this: if our understanding of how the MFA trip computer calculates mileage is correct, wouldn't this not be an issue?

Members told me, on another thread, that the MFA reads the cycle duty of the injectors and the mileage from the odometer to calculate the MPG. If we assume that gasoline with ethanol provides less MPGs, then wouldn't the injectors catch the decrease in mileage since they would be cycling more often? Because the MFA is reading close to what I would expect, but the hand calculation is showing less miles per gallon.

Here is the graph that shows my Hours Driven vs. the fuel disceprancy (what I figure the make up is between MFA and hand calculation).



Only the last 4 entries are actual hours driven (via the MFA) - prior to that I made some assumptions based on observations and driving cycle (urban versus highway). The date range runs from 02/21/2007 through 08/06/2007.

And here is a graph capturing every fuel fill since the car was new - and every time I buy gas it's a fill up. You can clearly see when things went goofy:

 

·
Registered
Joined
·
334 Posts
I agree with what you're saying -- basically, an explanation has to account for fuel that's not being measured by the MFA. There are two separate questions. 1) why is mileage lower? and 2) why are the calculations disagreeing. Most people seem to be answering 1) whereas 2) is probably more puzzling...
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #17 · (Edited)
I agree with what you're saying -- basically, an explanation has to account for fuel that's not being measured by the MFA. There are two separate questions. 1) why is mileage lower? and 2) why are the calculations disagreeing. Most people seem to be answering 1) whereas 2) is probably more puzzling...
Exactly.

The MFA was never entirely accurate from new, but it was, on average, about 1.3% optimistic. That remained true right up until February of this year. As it stands right now, I cannot break 30 MPG at the same speeds as driven in the past.

And a third question is: Is the discrepancy at all related to the overfill/overflow occurrence in February? Or is that just a coincidence? ("Coincidence is the word we use when we can't see the levers and pulleys." Emma Bull)
 

·
Banned
Joined
·
8,975 Posts
:) Yeah, I have a thread going re: gas mileage too.
1/2 a tank = 100 miles. And that's on a manual 5spd 1.8t.
no Aircon, no heated mirrors or heated rear windows, no roof rack, fan on low-mid and windows up. I put some air in tyres today, they were a little low.
Am going to change injector seals they are a bit leaky, Put in some slick 50 fuel system cleaner today as well. After that, will do the seals maybe slick 50 is a bit corrosive.
Do you think your driving style has changed? maybe your speed is wandering up and down according to pedal pressure?
For best gas mileage I used to find freezing the accelerator was best for eco,
let the car change speed (within reason) depending on hills.

I think the v6 are more economical! :)
Whoa! 200 miles to a tank? I get better than that driving in-city with the A/C on the whole way. (With an automatic!) I can get at least 400/tank driving cross-country.

When was the last time you changed your transmission oil? How about your CV joint grease? Are your wheels properly-aligned?

Berryman's Chemtool (in the metal can) is the only injector cleaner that I've ever felt any sustained improvement from -- most cleaners just boost your octane to make your car feel more powerful until the next fill-up, at which point you don't care anymore. Also, Seafoam administered with the help of the Black Seafoam Apparatus will help to restore off-the-line power if your intake valves are crudded-up and not seating properly.
 

·
Registered
Joined
·
7,582 Posts
Discussion Starter · #20 ·
STOP crying ! :poke: ...
you'll kill yourself if you had my mpg :p :biglaugh: (19-22mpg @ 60mph ----02 v6 4mo wagon)
Pfftt...I was on the web before I made my purchase and ruled out the V6 fomo thing for just that reason...:p :biglaugh: ... and that was when 93 octane was $1.50 a gallon!

I just didn't figure on my 1.8T droppin' down to FWD V6 mileage....
 
1 - 20 of 52 Posts
Top