Dismal MPG

MATPOC

Veteran Member
Joined
Dec 28, 2020
Location
Providence, near Hope
TDI
2003 Jetta Wagon 5-speed
Wheel alignment? Winter diesel fuel? Does a belly pan make a difference?
Alignment can't be far off, tracks straight and doesn't chew rubber, same fuel as IBW, he lives few towns over and gets at least 10 better MPG,
Not sure about belly pan, it's been off for most of the time because I've been playing with turbo actuator and looking for oil leaks
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
I got that 62mpg and reliable high 50s on my heavily fueld mk3 on 18s. As long as the tire size is within 3%of the oem size its fine!
You need a scangauge to learn real time mpg and gph. You are 90% of the equation
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Tire size (circumference) will affect the odometer results. Not sure how you are calculating your MPGs. But, if you don't factor for any deviation due to tire size, the calculation will not be correct, albeit small. And, other factors are involved (leverage) which affect the results. On-line tire size comparison calculators will be helpful.

The last 6 years of my career, from tank to tank (vented and filled to the rim), I consistently got over 50 MPG with my 2000 Jetta. Granted, I never drove faster than 75 MPH and mostly 70 MPH with a good amount of secondary roads which was in the 60s MPH range. I kept a very detailed Excel Spreadsheet. Including commute and on-the-job driving, I was doing about 36k miles per year. The ALH engine was totally OE, zero mods. I ran stock size tires. Today, at about 385k miles, my son is getting about 48 MPG with that car and he certainly doesn't drive like me.

I don't think I ever had the RPMs above 4100 and that was only once or twice. Briskly going up to 3200-3600 RPMs going thru the lower gears three or four times per tank of fuel provides adequate "blow-out" characteristics to keep the Turbo functioning just fine. So, I never had a Turbo issue of any kind. No, I never attempted to be a hyper-miler, but I did drive it to achieve what it was rated.

So, I believe the OP will never achieve good MPGs with all the mods as he'll always be tempted to test them. That's not saying there's some issues that may need to sorted out......... my 2 cents!
 

nokivasara

Veteran Member
Joined
Jan 25, 2008
Location
Sweden @ Lat 61N
TDI
Tiguan 4-motion, Golf mk7
Uncle Google says 39 miles per US gallon is 6.03 L/100K. Pretty much what I get on my ALH for city driving, as a datapoint.
We had our mk4 for about 7 years and never got that bad mileage. Best was 4,7l/100km and worst probably around 5,7, I think that's in the 40-50mpg range. Always filled to the brim and calculated like @AndyBees.
As a datapoint for a stock mk4 TDI :)
 

MATPOC

Veteran Member
Joined
Dec 28, 2020
Location
Providence, near Hope
TDI
2003 Jetta Wagon 5-speed
I know how to get good mpg, been driving for 30 years, pretty sure I got everything covered except maybe MAF or pump ...
I'm gonna do the logs and get some professional help.
 

nokivasara

Veteran Member
Joined
Jan 25, 2008
Location
Sweden @ Lat 61N
TDI
Tiguan 4-motion, Golf mk7
I know how to get good mpg, been driving for 30 years, pretty sure I got everything covered except maybe MAF or pump ...
I'm gonna do the logs and get some professional help.
Your mileage sure is too low, highway mileage should not be different with or without injectors/tune since you're not requesting more power than it takes to do 75mph. Other than timing being very retarded (causing smoke and bad mpg) there is not much more to check engine wise. you'd almost need a fuel leak to get that bad mpg doing 75mph.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
Sounds like a plan!
My 1st TDI 99.5 Jetta got 45 average. 50+ on straight highway (at 75-80). Dropped a bit after RC2 tune, but is was sure more fun. My (all stock) bug gets 38 city or highway, ruled out all the dumb stuff, suspect IP or injectors, but I drive the car so little, it's hardly worth the expense.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Sounds like a plan!
My 1st TDI 99.5 Jetta got 45 average. 50+ on straight highway (at 75-80). Dropped a bit after RC2 tune, but is was sure more fun. My (all stock) bug gets 38 city or highway, ruled out all the dumb stuff, suspect IP or injectors, but I drive the car so little, it's hardly worth the expense.
Bob, same here! I gave my son the 2000 Jetta and he don't drive it much because shortly thereafter he purchased an 04 with the BEW dirt cheap and low miles. Also, I purchased my brothers 03 with an 01 engine ............. I don't drive it much and I've not driven my 84 Vanagon with the 02 ALH in months .... Being honest and revealing, a little over a year ago, I purchased a very low miles 11 Tiguan with one of VWs biggest engineering goofs, the 2.0 TSI engine...... fuel economy sucks and it has a lot of potential issues of which some are beginning to show their ugly faces. But, the darn thing is awesome to drive.......... from about 2000 RPMs out to 5000 RPMs, it has 200 HP and 200 Ft lbs of torque ........flat on the graph! The 6-speed DSG is awesome!
 

CableJockey

Veteran Member
Joined
Apr 20, 2019
Location
South Dakota
TDI
2002 Golf GLS
Last fill up was 32 mpg with 1/2 city 1/2 highway...
Random thoughts:
-Have you verified your pump type? You mention you have a 5-speed, but have you verified that it still has the 10mm pump? 11mm might have been installed without your knowledge. (Check part numbers)
-You mention granny driving, but does it smoke if you lay into the pedal? (edit: noticed you said it does after 1/2 throttle...)
-Clear fuel lines still exist from filter to pump? Is there any air? Try watching the line while the engine is revved in neutral.... Excess air intrusion will screw with pump advance.
-You mention your tune is written to 25psi, yet boost holds steady at 30psi? That sounds like an issue that could be contributing. Do you have VCDS logs? If boost isn't trailing similar to expected, the ecu can do odd things with fueling to compensate.
-Do you use additives? Specifically winterizers/anti-gel? Some local stations near me sell "Power-service Xtreme diesel" which is pretreated with PS gray/white depending on season, treating such fuel again has resulted in noticeable MPG drops... sometimes dramatically so, if winterizer was involved.
 
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MATPOC

Veteran Member
Joined
Dec 28, 2020
Location
Providence, near Hope
TDI
2003 Jetta Wagon 5-speed
Random thoughts:
-Have you verified your pump type? You mention you have a 5-speed, but have you verified that it still has the 10mm pump? 11mm might have been installed without your knowledge. (Check part numbers)
-You mention granny driving, but does it smoke if you lay into the pedal? (edit: noticed you said it does after 1/2 throttle...)
-Clear fuel lines still exist from filter to pump? Is there any air? Try watching the line while the engine is revved in neutral.... Excess air intrusion will screw with pump advance.
-You mention your tune is written to 25psi, yet boost holds steady at 30psi? That sounds like an issue that could be contributing. Do you have VCDS logs? If boost isn't trailing similar to expected, the ecu can do odd things with fueling to compensate.
-Do you use additives? Specifically winterizers/anti-gel? Some local stations near me sell "Power-service Xtreme diesel" which is pretreated with PS gray/white depending on season, treating such fuel again has resulted in noticeable MPG drops... sometimes dramatically so, if winterizer was involved.
Didn't check pump number but I have all the service records since the car was new, didn't see anything about pump, but I will check. I did see bubbles but didn't think much of it, will check if still there. Sometimes it smokes at 1/2 throttle when I accelerate, not always.
Adjusted actuator on new turbo, still over 25 but not 30, also I never stay on the gas to even get past 15 psi, very light foot. I have another ECU with different tune that I will try swapping with next tank.
Fuel from few different places, Shell and Speedway usually, no additives AFAIK, like I said, everyone here uses same stations and no one has bad MPG.
 

CableJockey

Veteran Member
Joined
Apr 20, 2019
Location
South Dakota
TDI
2002 Golf GLS
I did see bubbles but didn't think much of it, will check if still there.
Sometimes it smokes at 1/2 throttle when I accelerate, not always.
These can be related: Consider the pump is ingesting air limiting the amount of fuel injected, ecu compensates by swinging QA, but the air is not constant: it varies. Going from large amounts of air to suddenly very little will result in ecu over-compensation and over-fueling until QA can adjust again.
I've had these problems: My car was ingesting huge amounts of air under load (hence my suggestion to watch the fuel line as the engine is revved, in my case air increased A LOT...) causing erratic smoke, and boost. Finding and fixing (most of) the air intrusion solved many problems for me....
 

NewTdi

Top Post Dawg
Joined
Jan 15, 2004
Location
NorCal
TDI
2003 Bora, Reflex Silver
Do you top off or just stop fueling when the pump stops? Right there you are loosing about 100 miles. If your tank is not vented you might want to try the Ventectomy mods. I have similar mods as Curious Cris and I am getting 40/44 mpg; if I drive at 65mph (odometer) I can squeeze 50mpg. Since the car is tuned because I wanted to have a more responsive car that is the price I had to pay. The best tank ever before mods was 62mpg, 99.9% highway trip. As other have mentioned dragging brakes, low tire inflation play a major role in FE/MPG. Difference between 15” and 18” wheels can be as great as 10mpg depending of tires and weight of wheels. If you are doing a lot of highway driving I would suggest getting a taller 5th gear; it makes highway driving more enjoyable and improves MPG between 3-5mpg.
 

MATPOC

Veteran Member
Joined
Dec 28, 2020
Location
Providence, near Hope
TDI
2003 Jetta Wagon 5-speed
These can be related: Consider the pump is ingesting air limiting the amount of fuel injected, ecu compensates by swinging QA, but the air is not constant: it varies. Going from large amounts of air to suddenly very little will result in ecu over-compensation and over-fueling until QA can adjust again.
I've had these problems: My car was ingesting huge amounts of air under load (hence my suggestion to watch the fuel line as the engine is revved, in my case air increased A LOT...) causing erratic smoke, and boost. Finding and fixing (most of) the air intrusion solved many problems for me....
What causes air ingestion? How did you address that?
 

MATPOC

Veteran Member
Joined
Dec 28, 2020
Location
Providence, near Hope
TDI
2003 Jetta Wagon 5-speed
Do you top off or just stop fueling when the pump stops? Right there you are loosing about 100 miles. If your tank is not vented you might want to try the Ventectomy mods. I have similar mods as Curious Cris and I am getting 40/44 mpg; if I drive at 65mph (odometer) I can squeeze 50mpg. Since the car is tuned because I wanted to have a more responsive car that is the price I had to pay. The best tank ever before mods was 62mpg, 99.9% highway trip. As other have mentioned dragging brakes, low tire inflation play a major role in FE/MPG. Difference between 15” and 18” wheels can be as great as 10mpg depending of tires and weight of wheels. If you are doing a lot of highway driving I would suggest getting a taller 5th gear; it makes highway driving more enjoyable and improves MPG between 3-5mpg.
I got this nailed down: fill up till I see fuel in the neck, wait for the foam to break down and I see clear fuel, go to the same pump, park in the same spot so if the car is slightly pitching up/down it's consistent.
Was getting similar mileage with 15's and 18's, also 2 different ECU's.
New pads, calipers and rotors, zero drag.... I wouldn't have been asking if it was something simple, I have extensive background in automotive field, just not familiar with diesels, if this was a gas engine I would have had it figured out by now because that's what I used to do for a living annd diagnostic is my favorite part (just doesn't pay ****)
 

CableJockey

Veteran Member
Joined
Apr 20, 2019
Location
South Dakota
TDI
2002 Golf GLS
What causes air ingestion? How did you address that?
In my case, it was bad fuel hoses/lines, bad thermo-t, tired spring Clamps, partially clogged fuel filter (mild fuel gelling during recent arctic temps), and a plugged/restricted fuel sender pickup.
The fuel restrictions allowed air to be pulled in readily through the ancient rubber fuel lines at higher revs. (These pumps have a lot of suction)
This was much exaggerated when I replaced my IP with an 11mm version with 250,000 less miles.

It was addressed by cleaning the sender pickup, drilling the check-valve restriction from the feed, replacing the fuel filter and fuel lines from the firewall to the IP. (I replaced my OEM clear lines with clear Tygon tubing from McMaster Carr)

I still get a trickle of very tiny bubbles, but that is acceptable compared to what it was prior.
Economy, smoke, and drivability all improved in my case...
 

red16vdub

Veteran Member
Joined
Aug 26, 2013
Location
(617) City of CHAMPIONS
TDI
03 JSW 5spd
Do you top off or just stop fueling when the pump stops? Right there you are loosing about 100 miles. If your tank is not vented you might want to try the Ventectomy mods. I have similar mods as Curious Cris and I am getting 40/44 mpg; if I drive at 65mph (odometer) I can squeeze 50mpg. Since the car is tuned because I wanted to have a more responsive car that is the price I had to pay. The best tank ever before mods was 62mpg, 99.9% highway trip. As other have mentioned dragging brakes, low tire inflation play a major role in FE/MPG. Difference between 15” and 18” wheels can be as great as 10mpg depending of tires and weight of wheels. If you are doing a lot of highway driving I would suggest getting a taller 5th gear; it makes highway driving more enjoyable and improves MPG between 3-5mpg.
Some tdi’s just get bad mileage, it’s something we can’t figure out just yet. I’ve always averaged around 45mpg city and usually 53-55 highway. 18” OEM wheels 225/40. I believe coolant temperature and tune plays a huge role in fuel economy. Just like IBW 700 tanks are normal. My best tank was 982 miles I think, heading to Miami with the wife before fuel light came on.
 

MATPOC

Veteran Member
Joined
Dec 28, 2020
Location
Providence, near Hope
TDI
2003 Jetta Wagon 5-speed
Put in new clutch last week, SB Stage2 Daily with SMF, new rear main and motor mounts. After 350 miles mostly around town and not particularly easy driving I got 38mpg...
Still smokes when I get on the power, mostly when I shift...
 

MATPOC

Veteran Member
Joined
Dec 28, 2020
Location
Providence, near Hope
TDI
2003 Jetta Wagon 5-speed
Thinking back to what else I did other than clutch before last fill up and just remembered that I pulled the MAF and rinsed it with light detergent and water, it seemed oily and I figured it's cheap enough to replace if I screw it up. Have not had any highway trips lately, so I'm not sure if this is now fixed, but 38mpg with heavy footed driving seems an improvement from 32 I got last time driving like a granny. I've been enjoying new clutch and getting little harder on the pedal, old clutch was slipping and I had to take it easy but was still getting 32mpg.
Smoking seems to come and go, seems sometimes I get on it more than 50% throttle and no smoke, other times it smokes heavy before I even get half way... wonder if I have an intermittent coolant temp sensor issue. Also I get a puff of black smoke if I shift at higher rpm.
Work and life been quite busy lately, it drives OK and broken strut bearing will be the next issue I will be addressing. 1000 miles on all new suspension and a pothole on i-95 bent a rim and broke strut top bearing... that is a kick in the balls
 
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TurboABA

Veteran Member
Joined
Jul 24, 2010
Location
Kitchener, ON
TDI
2010 Jetta 6spd MT, 2014 Touareg Execline
Hang on a sec.... so you're driving around with a slipping clutch, dirty and\or malfunctioning MAF and can't figure out why your MPG is suffering?
Could it possibly be impacted by the loss of power transfer and\or the inability to properly read airflow in order to supply the correct amount of fuel? :unsure:
 
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