Trying for better fuel economy...

[Reidjc0826]

Hey everyone so I've had my 1999 Mk4 Jetta for about a year and a half now. I have done everything you can imagine to this thing. Now, I'm just wanting to know how I can possibly get better fuel mileage. As of now I get around 450miles every tank. My car has the Borg Warner S7 turbo with bosio 520 injectors and the stock 10mm injection pump. From kermatdi I got their stage 1 tune. I have a 2.5 inch straight pipe all the way back. Not sure how much of a difference it would make but I also have the bbs336 wheels on it which are way heavier than the stocks. I have done brand new brakes all the way around as well to make sure they aren't hanging up. Just looking for the best ways I can get some better mileage.

If anyone had some ideas for me or needs more information please let me know.

 

[Reidjc0826]

Also usually I'm driving in the country 55-65 mph city/highway probably around 60/40%

 

[hskrdu]

Here's out go-to thread for FE:

tips for fuel economy

I've put this together in an effort to help some folks diagnose what may be a loss of fuel economy (MPGs) with their TDIs. Keep in mind, many of these items can work against your car in concert to add up to a sizeable increase in fuel consumption over time, so please don't dismiss any one item...

forums.tdiclub.com

If my MkIV got 450 miles to a tank, it would be cause for alarm! Swap out the wheels for something lighter with LRR tires...

 

[dieseldonato]

Even driving aggressively I still get close to 600 miles per tank.

 

[Reidjc0826]

Thanks guys I'll look into it are you guys sure it has nothing to do with the mods I've got on it.

 

[Reidjc0826]

Do you guys really think it could just be my wheels they are significantly heavier than my stocks but I'm not sure that, that is the only reason I'm getting this economy.

 

[Reidjc0826]

Also is it true with most city driving that you get around 35 mpgs because if so then it's not really that bad but I always thought I'd be getting more.

 

[burpod]

manual trans? 500 mi to a tank would send me into a frenzy. thats' not right. wife's BEW with an automatic will get 650mi easy before low fuel light comes on, with lots of short trips. somethins not right. could easily be part of the tuning

 

[burpod]

you said you did brakes... did you check, clean, and re-grease all the guide pins? mk4 front calipers (imo) dry out quick. it's a horrible design... i don't understand why more people don't have problems with it, or maybe they don't realize it (mk3 and earlier front calipers are better IMO). also, rear wheel bearings? those are easy to check. jack up the rear and spin the wheels. they should spin nice and free. take vcds logs... it will take some effort to figure out whats wrong. you could have hardware problems, tune problems.

 

[J_dude]

you said you did brakes... did you check, clean, and re-grease all the guide pins? mk4 front calipers (imo) dry out quick. it's a horrible design... i don't understand why more people don't have problems with it, or maybe they don't realize it (mk3 and earlier front calipers are better IMO). also, rear wheel bearings? those are easy to check. jack up the rear and spin the wheels. they should spin nice and free. take vcds logs... it will take some effort to figure out whats wrong. you could have hardware problems, tune problems.

Park brake cables can hang up too, though I’m sure all that is listed in the FE Thread linked above.

 

[dieseldonato]

Do you guys really think it could just be my wheels they are significantly heavier than my stocks but I'm not sure that, that is the only reason I'm getting this economy.

Don't know how it stacks up, I have 11mm ip, .230 injectors, and 1852 turbo. 43mpg is the worst I've seen normally closer to 48. Stock alloy wheels and stock size tires.

 

[Reidjc0826]

Right I feel like it should be getting more than I am. Also yeah checked the rears spin freely and fronts are new and checked all guide pins which were great and greasy. Yeah and brand new rear bearing and front bearings as well as suspension parts all the way around. Also, does vcds work on the early year Jetta because I have one of the ECUs you have to tune by having it repinned and I'd vcds does work I need to know which to get for mine and what to be looking for through it. I also like I said have wheels that are around 10lbs heavier maybe more for each. Not sure if that's what is doing it or not but never have really tested it either. Probably should. Let me know what you think.

 

[dieseldonato]

I thought vcds worked on all electronic tdi engines. Don't know anything about re pining an ecu just to pull codes, or reprogram. I've been using mpps v18 for that on my tdi.

 

[Zak99b5]

That seems like an extreme mpg penalty for heavier wheels; if you still have the stock Avus (or steelies), throw them on for a tankful.

As a side note, miles per tank isn’t very precise. Many people here remove the vent and can fit up to something like 16 gallons in it. My tank fill (still with vent) is more like 13. So I get 650 miles per tank, while the owner with vent removed gets 800 miles per tank, but we both are getting the same FE, 50 mpg.

 

[hskrdu]

Do you guys really think it could just be my wheels they are significantly heavier than my stocks but I'm not sure that, that is the only reason I'm getting this economy.

Also is it true with most city driving that you get around 35 mpgs because if so then it's not really that bad but I always thought I'd be getting more.

Your numbers suggest it's more than just wheels and tires, but using a light stock wheel/LRR tire combo will give you a baseline over a few thousand miles, and you can keep improving from there. Heavy wheels and tires often have a significant hit on fuel economy because of where the weight is located, and the energy it takes to get them rolling from a stop. It sounds like FE wasn't necessarily your main goal, but OH's thread is great resource once you've ruled out some common issues that sap economy. Over my first 200k miles my city fuel economy was around 42, but (as burpod noted) there's a notable difference between the manual and the auto trans. VCDS should work on your car, although some early years couldn't be flashed via OBD, which may be why you had to use a new chip- others could say for sure. And as Zak said, use pen and paper calculations on miles driven/fuel consumed for a MPG number, rather than miles per tank.

 

[Nevada_TDI]

With the mods you have you should still be getting a lot better FE.
Talk to @burpod here, he is really sharp on ALH engines.

 

[IndigoBlueWagon]

450 miles to the tank is not good, but how much fuel are you adding? If you're only filling with 9 or 10 gallons then things might be OK.

I have a '99.5 Golf with a Stage 3 tune, stock injectors and 10mm pump, and last fill was just under 49 MPG, and that included some pretty fast highway runs (90+ MPH). I usually get right around 700 miles to a tank, adding around 14 gallons.

 

[Reidjc0826]

I have been doing the numbers every tank fill up with 12.5 gallons as I'm not vented and I get around 35 mpg usually now like I said I do a lot of city driving like 35mph and sometimes up to 60mph. I'll definitely give @burpod a text see what he thinks. Also I don't know if I mentioned this but before I had done the brakes one of my rears was hanging up not terrible but was and now that I've fixed it and its not hanging up I haven't done a full tank but hoping to see a difference. Thanks guys really appreciate the insight like I said I'm not terribly new to these cars but also still am learning some things here and there.

 

[Reidjc0826]

Your numbers suggest it's more than just wheels and tires, but using a light stock wheel/LRR tire combo will give you a baseline over a few thousand miles, and you can keep improving from there. Heavy wheels and tires often have a significant hit on fuel economy because of where the weight is located, and the energy it takes to get them rolling from a stop. It sounds like FE wasn't necessarily your main goal, but OH's thread is great resource once you've ruled out some common issues that sap economy. Over my first 200k miles my city fuel economy was around 42, but (as burpod noted) there's a notable difference between the manual and the auto trans. VCDS should work on your car, although some early years couldn't be flashed via OBD, which may be why you had to use a new chip- others could say for sure. And as Zak said, use pen and paper calculations on miles driven/fuel consumed for a MPG number, rather than miles per tank.
[/QUOT

Hey not sure if I'm not with the lingo but who's OH

 

[hskrdu]

Hey not sure if I'm not with the lingo but who's OH

OH = Oilhammer, the OP for the FE thread I linked above.

 

[Reidjc0826]

OH = Oilhammer, the OP for the FE thread I linked above.

Oh alrighty thanks.

 

[Reidjc0826]

Also another thing who has suggestions on what Vag Com I need to be looking into because my father has an old set that no longer works so I'm going to have to invest a little. So any suggestions with the fact that my car is an early year Jetta TDI.

 

[burpod]

you should just go ahead and perform the free 5 minute "ventectomy" - get more consistent fill-ups topping off and more range on a tank

 

[Reidjc0826]

you should just go ahead and perform the free 5 minute "ventectomy" - get more consistent fill-ups topping off and more range on a tank

Agreed completely I think I'm going to today since I'm seeing it'll give me more range however I still would like to know how I can fix this 35mpgs if me fixing the rear brake hanging up a little doesn't work.

 

[burpod]

the other thing i would do before anything else, actually, if i didnt know who did the TB last, is verify cam/crank is spot on

 

[Reidjc0826]

the other thing i would do before anything else, actually, if i didnt know who did the TB last, is verify cam/crank is spot on
[/QUOT

Yeah I should I just need to do some research on how to since again I'm kinda new in thus world. I've worked on vehicles most of my life but these ones are a different breed.

 

[Nevada_TDI]

With the mods you have you should still be getting a lot better FE.
Talk to @burpod here, he is really sharp on ALH engines.

 

[454k30]

For accuracy, what is your actual fuel consumption in MPG or L/100km? This per-tank measure is useless as no one on this page is over-filling the tank until it spills and then driving until the car stalls from fuel starvation.

To answer your question though, your mods seem pretty standard in comparison to others who have some incredibly good efficiency numbers. The two biggest factors in mileage are rolling resistance and weight. Aerodynamics comes into play too, but only really heavily when the vehicles start to get over ~60mph.

Heavy wheels, wide/sticky tires, your precious pig-iron collection in the trunk are some of the most usual parasitic culprits. If you are in the higher highway speeds like in california or texas, then roof racks, wings or spoilers, missing or damaged body panels, etc. really start to take a toll on the mileage as well.

The speeds you mention are pretty low for most drivers. City driving will always eat more fuel because of the stop and go nature of traffic. When I was in maryland, I was fortunate if I saw 35 mpg. I had a short commute with about a dozen stop lights and bad traffic. Living in a rural WA, I would get something in the 45-48mpg range, with no mods done to the car, just no stoplights, no traffic, and low speeds. Now in Los Angeles, with heavy wheels and wide tires, roof bars, and driving 75+, I'm in the 40mpg club. Working with burpod, we likely have a couple of mpg we can get out of this thing, but I've created a car that is never going to see high 40's.