34MPG what to do

dave2500

Member
Joined
Jun 10, 2013
Location
Watchung NJ
TDI
00 auto
Hello,
I have a 00 jetta A4 250k miles

I just changed the fuel filter oil and filter, cleaned the egr and intake and did diesel purge

I am still only getting 34mpg

I use diesel fuel treatment in every tank

its about 60% highway 40% city and i buy all my diesel from BP (its a bigger truck stop one that sells a lot)

Any idea what to do

THanks
 

No More Buffalo

Veteran Member
Joined
Mar 31, 2012
Location
Greenville, NC
TDI
Current: 2015 Golf SEL 6m Sold: 2012 Golf 2dr DSG
Sounds like it's time to break out VCDS, check iq, check turbo boost vs requested, etc.

Does power seem ok? Checked the obvious stuff like a (very slightly) sticking parking brake?
 

MonsterTDI09

TDIClub Enthusiast, Veteran Member
Joined
Jul 3, 2009
Location
NoVa/NJ
TDI
2010 Jetta DSG/ up keep on 2009 Jetta DSG 2006 Jetta Pag 2 in North SEA Green
Hello,
I have a 00 jetta A4 250k miles

I just changed the fuel filter oil and filter, cleaned the egr and intake and did diesel purge

I am still only getting 34mpg

I use diesel fuel treatment in every tank

its about 60% highway 40% city and i buy all my diesel from BP (its a bigger truck stop one that sells a lot)

Any idea what to do

THanks
Did you just get this car? Stop and go and very hot days will kill mpg. Check you tire pressure. Check mpg by hand calculation and fill it to very top every time that will give you a true reading. Do this for a couple of tanks see what kinda number you get.
 

dave2500

Member
Joined
Jun 10, 2013
Location
Watchung NJ
TDI
00 auto
thats the adv of like 7 tanks

i had the car for like 40k miles now and i changed that fuel filter thinking that i got a bad batch of fuel but i guess not,


The tires are inflated right, i know that the timing belt is comming up for a change soon but i dont think that matters

When i first bought it i was getting a constant 40 with no problem
 

MikeMars

Veteran Member
Joined
Mar 6, 2008
Location
UK
TDI
Vento 1.9 TDi (retired), A4 1.9 TDi (rear end collision), VW Passat 1.9 TDi (retired), Audi A2 1.4 TDi
Firstly it's an automatic, which will drop your mpg significantly.

There are a couple more questions for which would be useful to know the answer.
* How many miles is your typical journey?
* What is your highway cruising speed?
 

Maffken

Veteran Member
Joined
Jun 14, 2013
Location
WNY
TDI
99.5 A4 Jetta ALH
Are your turbo lines good? My turbos been going on and off and it makes my engine work harder, until I replaced my pan and relubed my actuator I was only getting 28-35mpg. Water made it stick/rust and that caused more force on the failing lines, making them collapse.

I replaced all my small vac lines, check valve, maf and airfilter (it was due). I still think I have a leak somewhere but it's all working now :/.
 

BleachedBora

Vendor , w/Business number
Joined
Oct 16, 2003
Location
Gresham, Oregon
TDI
'81 DMC-12, '15 GL350 CDI 275 hp/448 tq - '81 Caddy CJAA, '05 E320 CDI 250hp/450 tq, '23 ID4 AWD Pro S Plus
That's a whole 'nother can of worms. Malone stage I is best mileage boost I've seen, and I'll even tell you not to go to me for it in an attempt to stay unbiased :p.
Your nearest dealer is Mike Hevner in Montague NJ. Great dude, he'll treat you well...
YMMV,
-BB
 

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
Maybe the fail-omatic 01M tranny isn't upshifting into 4th and/or the tcc is'nt going into lock-up mode. Any codes/CEL??
Also, try a few tanks w/o additive.
Timing matters, too.
Sounds like its due for a trip to the guru.
 

dave2500

Member
Joined
Jun 10, 2013
Location
Watchung NJ
TDI
00 auto
Maybe the fail-omatic 01M tranny isn't upshifting into 4th and/or the tcc is'nt going into lock-up mode. Any codes/CEL??
Also, try a few tanks w/o additive.
Timing matters, too.
Sounds like its due for a trip to the guru.

i did not have any for a while i use to have the speedomater go up when sitting at a light like up to 20 and the temp gauge will go down to 0

Then sometimes i get a cel light and the ac would not go on and it would not go into 4th

so i cleaned the intake and egr and the problems seemed to go away but i only did that 1 month ago,

so right now there are no CEL's
 

KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
currently 99 beetle and 2011 335d
If your MPG was good for a while, then suddenly/gradually took a dive, then something happened with the car to cause the MPG decline.

This is likely not something that a "chip" will fix on its own - unless somehow the "chip" comes with good support for helping you troubleshoot the underlying issue. (and the issue is something cheap/easy to fix)

Then, after troubleshooting, it may turn out to be a dying injection pump, clogged airway/head and/or cat/exhaust, boost leak, EGR leak, camshaft wear, sticking turbo, bad compression (from a number of causes), failed maf or coolant temp sensor, leaking thermostat, and so on.

Might only be a really hot summer and/or a bad batch(es) of fuel, filling the tank at half full vs almost empty, (believe it or not you will get better FE filling at the halfway mark instead of waiting until empty)

In other words, the car is not getting any newer, and may be due for some TLC that may or may not be expensive. But one thing is for sure: the MPG decline will not cure itself if there's an underlying mechanical problem, and if there's an underlying mechanical issue a tune will likely only make it worse without some troubleshooting, first.
 

dave2500

Member
Joined
Jun 10, 2013
Location
Watchung NJ
TDI
00 auto
If your MPG was good for a while, then suddenly/gradually took a dive, then something happened with the car to cause the MPG decline.

This is likely not something that a "chip" will fix on its own - unless somehow the "chip" comes with good support for helping you troubleshoot the underlying issue. (and the issue is something cheap/easy to fix)

Then, after troubleshooting, it may turn out to be a dying injection pump, clogged airway/head and/or cat/exhaust, boost leak, EGR leak, camshaft wear, sticking turbo, bad compression (from a number of causes), failed maf or coolant temp sensor, leaking thermostat, and so on.

Might only be a really hot summer and/or a bad batch(es) of fuel, filling the tank at half full vs almost empty, (believe it or not you will get better FE filling at the halfway mark instead of waiting until empty)

In other words, the car is not getting any newer, and may be due for some TLC that may or may not be expensive. But one thing is for sure: the MPG decline will not cure itself if there's an underlying mechanical problem, and if there's an underlying mechanical issue a tune will likely only make it worse without some troubleshooting, first.
What do i start looking at first, ?
 

raptor5618

Member
Joined
Mar 5, 2004
Location
Scranton PA
TDI
2011 Jetta
Had a 2001 TDI that I constantly checked the MPG at every fill up. I always had a drop in the winter. But when I saw a drastic change like that it either was the MAF sensor got gunked up, and I must have put 3 or 4 new ones in that care before I got rid of it. You can buy some cleaning solution for it but that only was a marginal fix. The other issue was The exhaust recirculating (ERG?) thing at the back of the engine. I only had the car for a little while after they switched to low sulfur fuel which was supposed to keep that from getting clogged but when that would clog, my mileage would drop. Lastly the biggest drop I had was when one of the connections at the injectors got a small leak. Mostly I could not tell that there was a leak except when I would sit with it idling with the windows open and I would get a wiff off fuel. I got mostly in the 38 to 39 range through the hills of PA. Automatic. I did get a small drop when I left the window heaters on while using the seat warmer. I rarely used the AC but did not see that big an effect when I did use it. Probably because it was only for short periods of time.
 

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
Film type material that the TDI MAF is made of don't usually fare well to cleaners, or oiled air filters like K&N type. There is no good reason for a MAF to get "gunked up". New OEM Bosch replacement MAFs are very good life now.
EGR shouldn't clog much now w/ULSD, mostly a thing of the past.
 

raptor5618

Member
Joined
Mar 5, 2004
Location
Scranton PA
TDI
2011 Jetta
Tried cleaning my MAF once and it really did not work so well as you said. Ended up just buying a new one. I know the new fuel is supposed to keep EGR's from clogging but back in the day it did cause me problems a few time.

All these problems presented themselves by giving me a big drop in power. I would notice that the car lacked that zip when trying to accelerate especially at higher speeds.

I think I also had a big drop when I had problems with the exhaust system. Not saying my problems are what problems he is having but thought my experiences might help. My thoughts are that something went south and it is not because of fuel.
 

Perfectreign

Veteran Member
Joined
Jul 20, 2013
Location
Los Angeles
TDI
2000 Jetta GLS 5-speed
(believe it or not you will get better FE filling at the halfway mark instead of waiting until empty)
I've never heard this.

Is there a rationale? I can't imagine 50 lbs. (approximately) of diesel fuel would make much of a difference. (I figure 7lbs/gallon x half-tank)
 

MikeMars

Veteran Member
Joined
Mar 6, 2008
Location
UK
TDI
Vento 1.9 TDi (retired), A4 1.9 TDi (rear end collision), VW Passat 1.9 TDi (retired), Audi A2 1.4 TDi
not the slightest difference. except maybe a miniscule drop in city driving mpg due to the extra weight.
 

KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
currently 99 beetle and 2011 335d
no,
the fuel heats up as it recirculates back the tank.
a fresh full tank is cooler fuel than if you run it until the low fuel warning.
You will gain maybe 5-10% fuel economy if you fill again after using less than 1/4 tank (fill again when the tankl is still almost full)
cooler fuel = denser fuel = more molecules oer gallon = energy density = fuel economy
or another way to look at it:
hotter fuel = less dense= fewer molecules per gallon etc

still using the same # of fuel molecules, just fitting more of them in a gallon = more MPG

this is one possible explanation, though there are others

This has been my personal experience: it works
All I can say is try it and see for yourself.

Fill the tank, vent
drive 100 miles or so
refill
observe fuel economy
repeat several times

then

fill the tank, vent
drive until on empty
refill
observe fuel economy
repeat several times

look at the difference

hypermilers will probably see less difference and the difference is more pronounced in the wintertime

won't change short trip economy as much

PITA to fill up every day if you have a long commute, but that's the choice you make, FE vs convenience
 
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Ultrasonic

Well-known member
Joined
Jun 10, 2012
Location
UK
TDI
Skoda Octavia 1.9TDi
cooler fuel = denser fuel = more molecules oer gallon = energy density = fuel economy
When people talk about mpg what matters surely is the number of miles per gallon of fuel purchased. Whether fuel expands or contracts a little in the fuel tank due to changes in temperature makes no difference at all to this. (Where temperature and fuel density does make a potential difference is connected to the time of day that you buy fuel, if the pump used doesn't have temperature adjustment.)

The only argument I've seen for it being better to keep a fuel tank full is that you get less fuel loss due to evaporation. But I suspect that this difference is tiny, and smaller than the already pretty trivial gains from the reduced weight of a partially filled tank.
 
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KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
currently 99 beetle and 2011 335d
All I can say is try it and see for yourself.

Fill the tank, vent
drive 100 miles or so
refill
observe fuel economy
repeat several times

then

fill the tank, vent
drive until on empty
refill
observe fuel economy
repeat several times

look at the difference

maybe a fluke, maybe I'm delusional, but I seem to be able to reproduce this fairly reliably over more than a decade of tdi ownership. So I have concluded that it matters
 
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Ultrasonic

Well-known member
Joined
Jun 10, 2012
Location
UK
TDI
Skoda Octavia 1.9TDi
maybe a fluke, maybe I'm delusional...
If you seriously think you get the 5-10% improvement in fuel economy you mentioned above then I'm sorry to say but I really do think that you are mistaken. There is simply no good reason why an effect of this size (or at all!) should occur. Unless, and this is monumentally unlikely, your car has some sort of fault that somehow causes it to behave in this way. Not that I can think of one that would (but I am not a mechanic).

If 5-10% fuel economy improvements really could be achieved in this way then car manufacturers would be selling cars with larger fuel tanks...

As you'll see from my Fuelly data, I sometimes fill up after a short distance, and sometimes when the fuel warning light comes on but there is no strong correlation with mpg.
 
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KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
currently 99 beetle and 2011 335d
ahh you have a PD... not relevant because the fuel temp is largely correlated to coolant temp and therefore stays relatively constant at the injectors (fuel flows thru the head)

My referenced TDis have all been rotary pump ALH (VE), sorry, should have specified
 

Ultrasonic

Well-known member
Joined
Jun 10, 2012
Location
UK
TDI
Skoda Octavia 1.9TDi
My referenced TDis have all been rotary pump ALH (VE), sorry, should have specified
I'll be interested in what others have to say, but I really don't believe the effect you describe occurs for ALH engines either.

You fill your car up with fuel. There is now a certain amount of energy (J) stored in the tank. If the fuel density changes the total energy doesn't change. To get an improvement in fuel economy (miles per gallon put into the tank) there needs to be an improvement in the engine power generated per J of energy in the fuel. Can you explain why this occurs, and if so why the effect should be as dramatic as you claim?
 

KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
currently 99 beetle and 2011 335d
1. speed of sound
2. isentropic bulk modulus (google it)

maybe should be another discussion thread. poor guys thread is hijacked
 

Ultrasonic

Well-known member
Joined
Jun 10, 2012
Location
UK
TDI
Skoda Octavia 1.9TDi
1. speed of sound
2. isentropic bulk modulus (google it)

maybe should be another discussion thread. poor guys thread is hijacked
I'm a scientist so technical terms don't intimidate me (and I don't need to Google bulk modulus to find out what it is) ;). Please do start a new thread to explain how these parameters relate to your argument and explain how refilling your tank at 1/4 full can lead to a 5-10% improvement in fuel economy. Right now I'm placing that claim firmly in the nonsense camp I'm afraid.

If your claim really is genuine the many people here with ALH engines will be very interested.

Edit: I'm not saying there is no effect, but I simply don't believe that if there is one that it can have anything like the scale of effect that you claim. A 10% increase in fuel economy is HUGE.
 
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