tips for fuel economy

TDeanI

Veteran Member
Joined
Oct 14, 2007
Location
Bremerton WA
TDI
'97 Passat TDI Wagon w/ 286K mi.
The hypermiller gurus say set to 0 degree toe in for best mpg, but I don't agree. The factree +value toe in settings are there for a reason. The suspension components have enough flex at highway speed that with positive toe in parked, you have 0 toe in at highway speed. Setting your car to 0 toe in, leads to Toe Out at 70 mph highway speeds and during braking which is unsafe. Toe out makes for very twitchy and unpredictable speed sensitive steering at 70 mph and is unsafe in my opinion. If you never driver your car over 45 mph, then 0 degrees toe in may work for you and save a percent or two in gas mileage.
 
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Alvis Adames

New member
Joined
Nov 23, 2022
Location
Asheboro, NC
TDI
2012 Passat TDI SEL Premium
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 because it may be just one small part of the puzzle, but an important part nonetheless! :)

Tires: this goes beyond simply air pressure, although that is an important part. Tread design is another, as well as the proper size and load rating. When in doubt, look at your car's tire information placard. It will have the proper size, load, and speed rating. Going from the proper 91 load to an 89 (an all too common mistake) can take a 1 MPG hit all by itself over the same model tire. Low Rolling Resistance (LRR) tires are becoming more popular, and are usually marketed as such. Still, keeping the pressure up, and the rating correct, is very important.

Alignment: if the alignment of the car is off, the tires can 'scrub' as they roll down the road. This causes excess friction and drag, which causes the engine to have to work harder. Checking the alignment with proper equipment is the only way to be sure everything is in specification. Worn bushings and steering components can cause the alignment to be out.

Trim pieces and shields: the car was designed to be both slick on the top AND the bottom. Missing shields under the car can not only make the engine take longer to reach operating temperature, they can also cause extra wind resistance when travelling down the road, and the faster you go, the worse it becomes. Missing grill inserts, missing lower splash shields, missing/damaged fender liners, can all contribute to this problem.

Thermostat: if the engine cannot reach proper operating temperature as quickly as possible and maintain it, it will cause more fuel to be used. Don't assume the gauge (or light in the New Beetle and latest Jetta sedan) is enough to tell you the engine coolant is warm enough. The only sure way to know is with a scan tool and watching the coolant temp data. Thermostats don't last forever, and one that cannot do its job properly needs to be replaced. If it gets really bad, the engine controller will flag a fault, however it has to be pretty bad before that happens. Also note that on many TDIs, the coolant temp sensors are notorious for going bad, so you may need to verify both sides (the ECU side and the Instrument side) is working on cars equipped with the 4-pin tandem CTS (specifically, late ALH, BEW, and BHW cars).

Timing: Both the VE TDI and the PD TDI are sensitive to timing. Just a few degrees can make a substantial difference. If the timing belt was installed wrong, your timing will be off. Period. While there is some sliding scale here, as some timing settings favor power over economy, keep this in mind when you set the timing after the belt is installed.

Air cleaner/air flow sensor (MAF): these items need to be in proper condition, and work in conjunction with the Exhaust Gas Recirculation (EGR) for proper engine function. A little bit off, or dirty, or poor quality/fitment can cause some adverse performance.

Lambda (oxygen) sensor (PD only): these can degrade and cause a slow response from the ECU in a similar (but not identical) fashion that a gasoline fueled car can, and can cause some loss of fuel mileage on PDs.

Intake/EGR clogging: while not the issue it once was, due to ULSD fuel, it is still something that should be checked for, especially on VE cars. This can cause a loss of power overall, and call for excessive fuel use since the air the engine needs to run cannot get in properly.

Brakes: many Volkswagens, especially A4 platform cars, have chronic stuck parking brake cables. This causes the rear calipers to drag, and your torquey diesel won't know it... it 'll just eat more fuel to move the car down the road. Also, brake pad perches can rust up, and cause the pads to sieze in their spots, dragging the brakes.

turbocharger: the "T" in "TDI" can't work properly if there is a vacuum/pressure leak, binding VNT/wastegate actuator, etc. While a fault will be flagged if it gets really bad, low boost can slowly creep up and rob you of both power and fuel economy gradually without you even knowing. Again, a scan tool checking requested and actual boost can help check the condition of your turbocharger system.

Driving style: we hear this all too often here, but it bears repeating here. Driving the car too easy for too long can really mess things up in the MPG department. Keeping the pipes clean, by occasional spirited driving, can help to keep the EGR clean, the intake clean, the intercooler clean, the breather system functioning properly, and the turbocharger working correctly, in addition to keep the catalyst and (where equipped) Diesel Particle Filter (DPF) clean and in good working order. A good test on VE and PD cars is to do a floorboarding rolling start (once the engine is warm) and see if it belches out a cloud of black smoke. A healthy, happy TDI, even a mildly modded one, should NOT do this. If it does, and it goes away after doing this a few times, you know you were driving it too easy for too long. Some folks call this an 'Italian tune up'. Whatever you want to call it, it works.

Excess weight: we can call this a minor one, but let's face it, dragging 50 pounds of tools, a stack of bricks, your entire CD collection, your golf clubs, the collected works of Charles Dickens, and 70 bottles of water around in your car is not really necessary.

Hopefully some of the above listed items can help you track down a possible loss of fuel economy! :)
What about cruise control ? you even mentioned and for me (15 year on a 2003 Jetta TDI) probably it gave you few miles per gallon extra
 
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kjclow

Top Post Dawg
Joined
Apr 26, 2003
Location
Charlotte, NC
TDI
2010 JSW TDI silver and black. 2017 Ram Ecodiesel dark red with brown and beige interior.
What about cruise control ? you even mentioned and for me (15 year on a 2003 Jetta TDI) probably it gave you few miles per gallon extra
Most would argue that they can get better mileage without cruise. You can react to upcoming terrain and traffic better then the cruise but I like not having to constantly feather the throttle on long trips.
 

Rumblebunny

Member
Joined
Apr 14, 2022
Location
Sacramento California USA
TDI
Mk4 ALH Beetle
Driving style: we hear this all too often here, but it bears repeating here. Driving the car too easy for too long can really mess things up in the MPG department. Keeping the pipes clean, by occasional spirited driving, can help to keep the EGR clean, the intake clean, the intercooler clean, the breather system functioning properly, and the turbocharger working correctly, in addition to keep the catalyst and (where equipped) Diesel Particle Filter (DPF) clean and in good working order. A good test on VE and PD cars is to do a floorboarding rolling start (once the engine is warm) and see if it belches out a cloud of black smoke. A healthy, happy TDI, even a mildly modded one, should NOT do this. If it does, and it goes away after doing this a few times, you know you were driving it too easy for too long. Some folks call this an 'Italian tune up'. Whatever you want to call it, it works.
From the original post.

So I have a dumb question: How should I do this 'Italian tune up'? My 2002 Beetle TDI has an automatic transmission; I'd know how to do this in a stick. Should I downshift it for a certain amount of time? Or should I go over 80 mph (which on the highway around here means keeping pace with traffic)? Where should my RPMs be, and for how long? 55-65 mph usually has me between 2100 to 2500 RPM. Or is there something else I should do?
 
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kjclow

Top Post Dawg
Joined
Apr 26, 2003
Location
Charlotte, NC
TDI
2010 JSW TDI silver and black. 2017 Ram Ecodiesel dark red with brown and beige interior.
when running the 55-65, just drop it down a gear or two. You're still not going to push redline.
 
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Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
Just fit it into your normal driving and do it when the opportunity presents itself. Long open onramps to the highways and such. No need to do anything drastic in traffic. This should be easy to accomplish.
 

braddies

Veteran Member
Joined
Jul 26, 2021
Location
America
TDI
03 golf ALH
Still confused why peeps are coasting in neutral... Especially when it means using more brake pads and rotors.
On the ALH at idle the scanguage says it uses 0.11Gallons Per Hour, so coasting either in neutral and/or with clutch in 0.11gph is a given.

When going downhill in gear with no throttle input consumption drops to 0.01Gph. Scanguage will indicate hundreds, sometimes thousands of instant mpg as the weight/momentum of the car pulls the motor downhill.
Where if the car was left in neutral you're only looking at 200-300mpg going down the same hill.

Imagine one would probably have to be pretty good at rev matching to avoid prematurely wearing the clutch and syncros.
After reading a few pages of this thread just curious, it just feels weird to be in neutral anywhere but at a red light.
 

Ragdude

Veteran Member
Joined
Aug 18, 2021
Location
Phx
TDI
2015 VW Golf SEL TDi
Still confused why peeps are coasting in neutral... Especially when it means using more brake pads and rotors.
On the ALH at idle the scanguage says it uses 0.11Gallons Per Hour, so coasting either in neutral and/or with clutch in 0.11gph is a given.

When going downhill in gear with no throttle input consumption drops to 0.01Gph. Scanguage will indicate hundreds, sometimes thousands of instant mpg as the weight/momentum of the car pulls the motor downhill.
Where if the car was left in neutral you're only looking at 200-300mpg going down the same hill.

Imagine one would probably have to be pretty good at rev matching to avoid prematurely wearing the clutch and syncros.
After reading a few pages of this thread just curious, it just feels weird to be in neutral anywhere but at a red light.
Yup , what little you might save in fuel would be quickly eaten up on wear/tear on all other parts
 

J_dude

Veteran Member
Joined
Jan 9, 2020
Location
SK Canada
TDI
2003 1.9l “Jedi”
Still confused why peeps are coasting in neutral... Especially when it means using more brake pads and rotors.
On the ALH at idle the scanguage says it uses 0.11Gallons Per Hour, so coasting either in neutral and/or with clutch in 0.11gph is a given.

When going downhill in gear with no throttle input consumption drops to 0.01Gph. Scanguage will indicate hundreds, sometimes thousands of instant mpg as the weight/momentum of the car pulls the motor downhill.
Where if the car was left in neutral you're only looking at 200-300mpg going down the same hill.

Imagine one would probably have to be pretty good at rev matching to avoid prematurely wearing the clutch and syncros.
After reading a few pages of this thread just curious, it just feels weird to be in neutral anywhere but at a red light.
The trick is to time it so you can coast up to corners and such, in neutral, and not have to use the brakes. Kinda takes some finesse to accomplish, and not recommended in traffic for sure but I do it on my rural commute. No idea if it is actually better than leaving it in gear but I find it an interesting pastime on my boring drive, trying to time it right so I can end up going the right speed when I approach my turn. Lol

Edit: Also, how do we know the scangauge is actually giving real numbers at idle and during overrun? Like a calculator displaying ERROR when you enter an actual number that is just too long for its display, a “real info is being typed in, fake numbers comin out” situation? No idea ignoring that’s a possibility, but just throwing it out there.
 
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braddies

Veteran Member
Joined
Jul 26, 2021
Location
America
TDI
03 golf ALH
The trick is to time it so you can coast up to corners and such, in neutral, and not have to use the brakes. Kinda takes some finesse to accomplish, and not recommended in traffic for sure but I do it on my rural commute. No idea if it is actually better than leaving it in gear but I find it an interesting pastime on my boring drive, trying to time it right so I can end up going the right speed when I approach my turn. Lol

Edit: Also, how do we know the scangauge is actually giving real numbers at idle and during overrun? Like a calculator displaying ERROR when you enter an actual number that is just too long for its display, a “real info is being typed in, fake numbers comin out” situation? No idea ignoring that’s a possibility, but just throwing it out there.
Oh yeah these are the little things that makes these cars Fun!
The scanguage 2 can track tank by tank averages, when you refill there's a menu to enter in how many gallons you filled up with and the amount fuel it "thinks" was used, it's usually agreeing with the pump with an error of ~0.1-0.2 gallons...

When decending downhill monitoring MPG, GPH and Throttle Position Sensor it can read up 9999 mpg at 0.01gph and 0 tps, but the cool part is feathering in the throttle while slowing down gradually going uphill waiting to crest the peak, losing a couple mphPerSecond but staying over 50mpg.
 
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Ragdude

Veteran Member
Joined
Aug 18, 2021
Location
Phx
TDI
2015 VW Golf SEL TDi
...
When decending downhill monitoring MPG, GPH and Throttle Position Sensor it can read up 9999 mpg at 0.01gph and 0 tps, but the cool part is feathering in the throttle while slowing down gradually going uphill waiting to crest the peak, losing a couple mphPerSecond but staying over 50mpg.
Please tell me the speed limit on this road you're traveling is 50 mph, or there is no one behind you when playing these silly games
 

ezshift5

Veteran Member
Joined
Sep 2, 2003
Location
West Coast
TDI
2013 JSW TDI (Enroute BB).......2017 Jetta 1.4 turbo 5M ....................
Around here - 500 miles north of San Diego - the popular culture is to accelerate INTO a red light.

Honestly - I am appalled at the level of discourtesy, ineptitude and deportment of a very high percentage of MV operators around our state capital....................

I am on my 21st year of zero accidents, citations and/or claims. i used to like to drive. Guess what? Not so much these days.

Some time I daydream about returning to my college days - with a Ford Fairlane 500 convertible...........


ez
 

Rumblebunny

Member
Joined
Apr 14, 2022
Location
Sacramento California USA
TDI
Mk4 ALH Beetle
Around here - 500 miles north of San Diego - the popular culture is to accelerate INTO a red light.

Honestly - I am appalled at the level of discourtesy, ineptitude and deportment of a very high percentage of MV operators around our state capital....................

I am on my 21st year of zero accidents, citations and/or claims. i used to like to drive. Guess what? Not so much these days.

Some time I daydream about returning to my college days - with a Ford Fairlane 500 convertible...........


ez
Here in Sacramento, we also have THAT GUY, which is why I pause at least 3 seconds before starting through an intersection.
 

Ragdude

Veteran Member
Joined
Aug 18, 2021
Location
Phx
TDI
2015 VW Golf SEL TDi
Around here - 500 miles north of San Diego - the popular culture is to accelerate INTO a red light.

Honestly - I am appalled at the level of discourtesy, ineptitude and deportment of a very high percentage of MV operators around our state capital....................

I am on my 21st year of zero accidents, citations and/or claims. i used to like to drive. Guess what? Not so much these days.

Some time I daydream about returning to my college days - with a Ford Fairlane 500 convertible...........


ez
Same here, I really wish every intersection would have red light runner cameras, and make the fines hurt more with each offense. Being stupid should be painful, maybe it'll sink in.
 
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Zak99b5

Veteran Member
Joined
Apr 30, 2021
Location
Albany NY
TDI
2003 Jetta TDI
Maybe it’s a Dem state capital thing? Here in Albany NY a red light means one more car can go through. Ok, sometimes two cars.

We have a few red light cameras, but if they stop for that one they run the next three.
 

kjclow

Top Post Dawg
Joined
Apr 26, 2003
Location
Charlotte, NC
TDI
2010 JSW TDI silver and black. 2017 Ram Ecodiesel dark red with brown and beige interior.
When one of my co-workers was returning to Europe, he said that he finally figured Charlotte traffic out. Yellow means three more and red means five more. I think it's only gotten worse over the last 20 years. Everyone recognizes the problem, but the cops are too busy elsewhere to enforce traffic laws. As a kid in Iowa, I was issued a warning for running a yellow light!
 
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TDeanI

Veteran Member
Joined
Oct 14, 2007
Location
Bremerton WA
TDI
'97 Passat TDI Wagon w/ 286K mi.
I coast every chance I get. My Scan Gauge 2 says I use 0.16 gph at idle warmed up, which isn't much, but coasting downhill in gear I go from around 100 mpg to around 400 mpg after shifting to neutral on the Scan Gauge II when coasting at highway speeds. On my 35 mile each way commute I probably coast at least 4 miles if I added them all up. It does make a difference but not a lot, maybe 5% increase in trip gas mileage. The biggest difference is the length of the coast. I have one coast on my commute that is about 3/4 mile long if I am in neutral but only about 1/2 mile if I leave it in gear and coast. The motor does slow down the vehicle some.

The brakes on a B4 wagon are undersized anyway. You have to push in the clutch on an emergency stop or the motor will fight the brakes and take longer to slow down in a panic stop. First time I had to do a panic stop on the freeway I almost hit the car in front of me. Around 30 mph the motor starts bucking against the braking.

Around here most people stop on reds unless it is a notoriously long left turn signal, then you get a few late comers, but the lights are timed with a long delay that a few can make it through before the other direction turns green.
 
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braddies

Veteran Member
Joined
Jul 26, 2021
Location
America
TDI
03 golf ALH
I coast every chance I get. My Scan Gauge 2 says I use 0.16 gph at idle warmed up, which isn't much, but coasting downhill in gear I go from around 100 mpg to around 400 mpg after shifting to neutral on the Scan Gauge II when coasting at highway speeds. On my 35 mile each way commute I probably coast at least 4 miles if I added them all up. It does make a difference but not a lot, maybe 5% increase in trip gas mileage. The biggest difference is the length of the coast. I have one coast on my commute that is about 3/4 mile long if I am in neutral but only about 1/2 mile if I leave it in gear and coast. The motor does slow down the vehicle some.

The brakes on a B4 wagon are undersized anyway. You have to push in the clutch on an emergency stop or the motor will fight the brakes and take longer to slow down in a panic stop. First time I had to do a panic stop on the freeway I almost hit the car in front of me. Around 30 mph the motor starts bucking against the braking.

Around here most people stop on reds unless it is a notoriously long left turn signal, then you get a few late comers, but the lights are timed with a long delay that a few can make it through before the other direction turns green.
clutch usually gets disengaged during a quick stop until we know what gear to throw it into, idk about this "coasting in neutral," seems to pale in comparison to the mpg we get with a skillfully modulated right foot.

On a side note, met a left-foot-brake-pedal guy the other day and his taillights were blinking going down the highway and don't know how communicate to him about how many extra brake pads he goes through every year. Happy New Year!
 
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hskrdu

Top Post Dawg
Joined
Oct 17, 2003
Location
Maryland and New England
TDI
2003 Golf GLS 4D 5M, 2015 GSW SE 6M
I coast every chance I get. My Scan Gauge 2 says I use 0.16 gph at idle warmed up, which isn't much, but coasting downhill in gear I go from around 100 mpg to around 400 mpg after shifting to neutral on the Scan Gauge II when coasting at highway speeds. On my 35 mile each way commute I probably coast at least 4 miles if I added them all up. It does make a difference but not a lot, maybe 5% increase in trip gas mileage. The biggest difference is the length of the coast. I have one coast on my commute that is about 3/4 mile long if I am in neutral but only about 1/2 mile if I leave it in gear and coast. The motor does slow down the vehicle some.
Not sure about the 1Z/AHU, but the ALH uses less fuel coasting in 5th than coasting in neutral. Try your readings with VCDS, you may find highway in neutral is less efficient.
 
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dhangejr

Veteran Member
Joined
Mar 1, 2017
Location
PNW is my home
TDI
mk4 Jetta
Driver slow and get the best MPG
I can get 42 in town driving slow.
I like to go so I get 37.

Highway is same story. Keep it at 60 I get 49 pretty much always. Go 80 I get 44 pretty much always.
 
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Ragdude

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Joined
Aug 18, 2021
Location
Phx
TDI
2015 VW Golf SEL TDi
... On a side note, met a left-foot-brake-pedal guy the other day and his taillights were blinking going down the highway and don't know how communicate to him about how many extra brake pads he goes through every year. Happy New Year!
There are a LOT of apparently left foot brakers, even if you don't think you're applying the brake, you are. Just got home from a New Years getaway and the number of idiots braking while traveling down the freeway is depressing. Set your cruise control, plant your feet on the floor, and enjoy the drive.
 
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dhangejr

Veteran Member
Joined
Mar 1, 2017
Location
PNW is my home
TDI
mk4 Jetta
I like to practice my heal toe technique. I often wonder what people are thinking With my brake lights blinking. It’s also fun When people are on my ass,
 
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Ragdude

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Joined
Aug 18, 2021
Location
Phx
TDI
2015 VW Golf SEL TDi
I like to practice my heal toe technique. I often wonder what people are thinking With my brake lights blinking. It’s also fun When people are on my ass,
I know what I'm thinking
 
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turbodieseldyke

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Joined
Jun 6, 2010
Location
Free Mustache Rides
TDI
98 jetta
Not sure about the 1Z/AHU, but the ALH uses less fuel coasting in 5th than coasting in neutral. Try your readings with VCDS, you may find highway in neutral is less efficient.
AHU works the same. Using TDeanI's example:
I have one coast on my commute that is about 3/4 mile long if I am in neutral but only about 1/2 mile if I leave it in gear and coast. The motor does slow down the vehicle some.
he loses 1/4 mile of coasting by leaving it in gear. Coasting in neutral during that extra 1/4mile costs him about 0.12gal/hour * 0.0042hour, or 0.0005gal. Coasting in 5th saves him 0.0005gal, but costs him much more than that to regain his original speed.
 

turbobrick240

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Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke
I know some people make a big deal about coasting in neutral being lethal and all that, but I do it frequently since there is very little traffic in my area- and it's pretty hilly. Not as much in winter when the road surfaces can get slick. I definitely coast much further in neutral than in gear. I just enjoy maximizing the coast more than the fuel it saves.
 
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J_dude

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Joined
Jan 9, 2020
Location
SK Canada
TDI
2003 1.9l “Jedi”
There are a LOT of apparently left foot brakers, even if you don't think you're applying the brake, you are. Just got home from a New Years getaway and the number of idiots braking while traveling down the freeway is depressing. Set your cruise control, plant your feet on the floor, and enjoy the drive.
Just a note; not all left foot brakers are idiots, I mean I’m sure lots of them probably are, with the number of idiots in the world in general lol, but I know from my work operating equipment you OFTEN need to use both feet (one on each pedal, the machines are made for this) for better and smoother control, and I can see how some people might end up making that a habit in their personal vehicle. I personally don’t do this unless the situation calls for it (like rocking the vehicle back and forth to get unstuck, things like that) and then only in vehicles with two pedals (naturally your left is busy with the clutch in cars with manual trans).
 
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kjclow

Top Post Dawg
Joined
Apr 26, 2003
Location
Charlotte, NC
TDI
2010 JSW TDI silver and black. 2017 Ram Ecodiesel dark red with brown and beige interior.
yup, kind of hard to ride the brake when you have a clutch.
 
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