Quest for better fuel economy

I have had my 2003 Jetta TDI sedan since November, 2017. When I bought the car (before I did anything to it) I was getting 34 mpg in the city. When I do city driving, I do about 25% highway driving. After I replaced the thermostat and replaced the rear calipers, my mileage went up to 38.5. That was just one tank though. I then replaced the fuel injectors and did a tune from Kerma. I had Charlie do a performance/economy tune and ended up with 36.5 mpg on the next tank. I then went back to Charlie and had him do a pure economy tune. I'm going to get about 36.5 mpg on my current tank as well with the economy tune.

There at people on here that get 42 mpg in the city with the same engine/car.

Should I just give up in my quest for better FE and be happy with 36.5? Does anyone have any suggestions for things to check?

Here is what has been done to the car in my quest for better FE:

* Replaced intake manifold (old one was 40% coked up - did not clean out the intake ports on the head)
* Replaced ASV valve (old one was coked up)
* Replaced both rear calipers (old ones were dragging, new one spin freely)
* Cleaned snow screen. (40% clogged)
* Checked injection timing with Vagcom. Set to intersect with green line.
* Set IQ to 3.0. (I had this at 5.8 and Kerma told me to set it to 3.0. Didn't make any difference)
* Tire pressures are at 45 psi.
* Replaced all of the smaller vacuum lines.
* Replaced turbo actuator. (It is adjusted correctly)
* Tested N75 valve.
* Replaced MAP sensor.
* Replaced fuel filter and air filter.
* New timing belt, rollers, etc 1 year ago. (Done by previous owner at Autobahn Motorworks in Phoenix)
(static timing has not be rechecked, but I think this is a VW knowledgable shop)
* I try to keep the car at 2000 rpm when not accelerating.
* I use 5th gear whenever possible down to 45 mph.
* Replaced vacuum reservoir and brake master vacuum hose with new ones.
* Tested vacuum and got 24".
* Did full EGR delete.
* Checked intercooler and no oil came pouring out of it. (removed the hose from the turbo to check it)
* Checked engine temperature multiple times. (Average 188-195 degrees F)
* Cat and muffler were replaced with a straight pipe.
* Checked odometer against GPS and I am correcting the mpg figures.
* Installed Panzer plate to replace missing bottom engine cover.
* Replaced thermostat and coolant temperature sensor.
* Adjusted turbo actuator so it has the correct amount of boost. (used Vagcom)
* Fixed cap on the top of the fuel tank. (wasn't screwed in and was leaking fuel)
* Replaced fuel injectors with Bosio DLC 520 injectors.
* Did KermaTDI tune with EGR delete.
* Front end alignment done recently.

Thanks!

There's a sticky over in the Fuel Economy thread. It will likely help you out...

http://forums.tdiclub.com/showthread.php?t=342274


By the way, your location reads Florida. Why do you have a snow screen on your air filter?

Also, I use a ScanGuage II in my car, and have for years. If you are trying to get the best economy I'd recommend one of these. There are other brands that do the same thing. Whichever suits you better.

Thanks, I have read the FE thread many times. I just read it again and I have done everything on that list. I am in Albuquerque, NM. I have the Torque app for my phone and that shows realtime FE.

Wow you've checked pretty much everything.
Is this purely city driving? Often the bias on forums like this is to overestimate mpgs, so comparing one's city driving to another's is difficult.


How many miles on engine?

Transmission fluid? (Doubtful)

You can adjust IQ either way and your dash display (fuel consumption) will increase or decrease depending on the direction of that adjustment. I gather you aren't doing your calculations with pencil and paper.

Random thought, but: what wheels and tires are you running?

Your city numbers are very close to what I get during the warm months. I'm running a heavy 17" 'Longbeach' wheel in the summer, which contributes to lower city economy.

Have you tried to take a non-city driving trip to see what you can get out of a tank? If I can do 80%+ highway, I get between 46-51 MPG for the tank. My city mileage is still sub-40, though.

I see lots of MPG claims on these forums that I've never been able to attain. Not sure how some folks come up with their numbers as I have 115k miles worth of fill-up data where I fill to the same spot in the filler neck each time. Each car is different and you'll drive yourself crazy trying to match the figures someone else has posted.

iirc, the EPA mileage on the window sticker for a 5-speed manual ALH was 42 city/49 highway.

I've been part of the 800 mile club before, which was a road trip from NJ to Detroit area, but this was before the modding started. This was also with the stock Low Rolling Resistance tires (Michelin Energy MXV4 Plus).

Swap the wheels and tires from daughter wrecked car and check, might be the wheels.... still in Texas, will call you when I get back. You should be getting better mileage for sure.

I am running 17" wheels. I already swapped in the 15" wheels from my 99.5 and it made no difference. I am doing the mpg calculations by hand and using Acar as well. My mpg calculations are spot on.

210,000 miles. I recently changed the transmission oil. I have not tried a highway only trip yet.

Thanks everyone!

Tires/wheels can make a diff, but not that much IMO... my son drives an 01 golf with 17" fat fives and 225 tires. He can still get over 50. I don't know how heavy those wheels are tho. We run 195's on the BEW and my DD has 16" with 205's. I can get really good numbers in each of those.

The biggest factor I've seen is driving habits - my wife gets high 30's low 40's in her current DD (BEW 5 speed). I drove that car over 3 years and had a 50.6 running avg. There is a commute difference but she routinely shifts BEFORE the tach gets to 2k and she rarely rolls in neutral. While it was still my DD, I could tell which tanks she drove the car because my numbers would be lower.

That being said... "city" driving for us is pretty rural compared to most. We are rarely in stop and go traffic or "light to light" situations.

I'd definitely take it on a highway run and keep it at 70 - you should score 50mpg if not really close.

Tires/wheels make a gigantic difference when doing mostly city commuting. When I ran the stock 15" wheels with factory tires my MPG was right around where the EPA put it. My 17" 'Longbeach' wheels kill city economy due to larger rotational mass. I can still "get over 50" with these wheels if I'm doing all highway driving, but my city driving just plummets.

Like mentioned above, driving habits also have a decent effect. I'm more heavy footed with my VNT17 and Stage 4 tune compared to stock as I like the power.

For a manual transmission car that FE is pretty low. I can count on my thumbs the number of tanks where I've gotten less than 40 MPG in my '02 Wagon. I'd look at four things: boost, injector balance, static and dynamic timing, and MAF performance. Sounds like you've checked or improved most other stuff.

In my experience static timing is important. And if your turbo isn't meeting requested boost levels it'll result in a loss of FE. Same if it's persistently overboosting. You can run fueling, boost, and MAF logs in VCDS and see how well each area is meeting requests.

I think these cars tend to deliver lower FE in arid climates. And in most western cities you end up stopping at a light, accelerating to 50+ MPH, then stopping again. I find that's hard on FE. Nevertheless, you should see at least 40 MPG in the worst conditions.

mrfiat said:

I am running 17" wheels. I already swapped in the 15" wheels from my 99.5 and it made no difference. I am doing the mpg calculations by hand and using Acar as well. My mpg calculations are spot on.

210,000 miles. I recently changed the transmission oil. I have not tried a highway only trip yet.

Thanks everyone!

Click to expand...

What did you put in for tranny oil?

Also, is there any chance the AC is overfilled? Probably a mild contributor, but possible.

My injectors were pop tested and balanced by Kerma, so that shouldn't be an issue. Here is the Group 13 readings: .14 -.16 .0 .33 All within 0.5, so I should be ok there.

I used synthetic 75W90 in the transmission. I don't know what brand it is.

I did have a thread on here asking about my boost levels when I was adjusting the actuator. Everyone seemed to think my boost graph looks fine. I can post it again if needed?

By dynamic timing you mean the injector timing? If so, that is set to the green line.

No idea about the A/C being over-filled. I do have an A/C gauge set, so I can check that if people think that could be a problem. I was driving this car in the winter and the mileage wasn't any better with no A/C running. The car does lug a little when you turn the A/C on which could be a sign of the A/C clutch going out. My other two ALHs do not do this.

I will try the fueling and MAF logs to see how those look thanks! I have not checked the static timing, not sure how hard that is to do. I am installing a new timing belt soon in my wagon, so I will need to do it for that anyways.

True if air is overfilled mileage will really suffer !!!!!!!happened to one of my jettas.

There's been discussions about using different tranny oils for years. Make sure you used a GL4 rated oil. I noticed a difference when I changed to RedLine MT-90. Notchy, and car seemed a little sluggish when warmed up. I bought the VW tranny oil from the local VW stealer and put that oil back in. Brought the car back to normal. The 75W90 oil is considerably thicker than the factory fill oil.

I used this howto and they say to use 75W90, so I did.

http://www.myturbodiesel.com/wiki/m...iy-service-and-fluid-replacement-mk4-vw-audi/

I was having problems at times shifting into 4th gear and all the problems went away after I changed the transmission oil.

Unless you are looking for bragging rights, the extra MPGs aren't going to make a big difference in the wallet. I average 41MPG and fuelly tells me if I got 3 MPG better I'd save $4 a tank. That's $100 a year in my situation. I'm paying just under $5/gallon too.

The money for fuel is not really an issue for me. Part of what I love about the TDIs is their excellent FE. My car runs excellent, has great power, starts instantly, doesn't smoke, and looks great, so I am very happy with it.

I would just like my car to get the best FE that it can possibly get. It seems like I am short at least 4 mpg in the city.

ffemtp said:

There's been discussions about using different tranny oils for years. Make sure you used a GL4 rated oil. I noticed a difference when I changed to RedLine MT-90. Notchy, and car seemed a little sluggish when warmed up. I bought the VW tranny oil from the local VW stealer and put that oil back in. Brought the car back to normal. The 75W90 oil is considerably thicker than the factory fill oil.

Click to expand...

Had none of those issues with Amsoil MTG 75w90 GL-4

For me it's not about the money, really, either. Although I don't mind the savings.

This stuff just never gets old. My most recent fill:

Get a Scangauge. That allowed me to get feedback on how effective my driving habits are. I've been able to consistently get 50 mpg over my 20 mile mile commute, and 60+ on road trips through the Colorado mountains.

Dumb stuff- If the outside diameter of the wheel is not real close to factory, the calculation needs adjusted.

802 Impressive! My best is 585 in town with this car. I did 625 miles in my new wagon before I filled up, but that was all highway miles with a slushbox. I'm in the process of doing the 5-speed swap now. Once I finish that, then I will do a tank here in town and see if the wagon gets better FE than the sedan has been. That will help determine if it is the car or my right foot that is the problem.

I got that tank commuting, some traffic, lots of suburban driving, running at 80+ on the highway when traffic allowed. So I was hardly hypermiling. However, I was surprised at the range on that tank. Usually I get 720-750 in similar driving.

I assume that was the wagon?

Even being careful, I've never seen anywhere near that sort of range on my sedan. My best have been barely flirting with 700 miles.

Are the timing belt tools required to check the static timing?

Yes.
You can improvise.
You can not compromise.

Yes, the wagon. Light had just come on and I put in 15.6 gallons. Can get right around 17 in it if it's really empty. I can't get that much fuel in my MKIV Golf.