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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old August 4th, 2019, 15:14   #16
ffemtp
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This might be a statement of the obvious, so forgive me....

How about checking / changing the AIR filter? I would not assume the stealer changed that when they did the "fix" or prepped the car for sale. If the car sat for a year + you might just have yourself a critter nest in there. Less than 5 minutes and a screwdriver and you'll have that verified.
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Old August 4th, 2019, 17:32   #17
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Quote:
Originally Posted by 35 Yr Dsl Veteran View Post
A clogging air filter does NOT decrease MPG in a computer controlled, fuel injection engine. Only in the old days with carburetors would it have made any difference. The only effect will be less air flow and fuel flow to compensate, resulting in lower HP, top speed, and acceleration. Under those conditions, you will actually get GREATER MPG!
I said nothing about mileage. I made a suggestion to check / replace the air filter. Period. Nothing more. I'll take a clean air filter over a dirty / clogged one any day of the week and twice on the weekend.
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Old August 4th, 2019, 22:47   #18
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Quote:
Originally Posted by 35 Yr Dsl Veteran View Post
If something was wrong, such as retarded injection timing, it would be putting out lots of soot. He did not specify thusly.
This is a modern diesel engine with a dpf filter. It would be next to impossible for it to put out lots of soot unless the dpf filter was cracked or broken in some way. If it was putting out huge amounts of soot it would be almost unnoticeable except for the fact it would be doing a dpf regeneration really, really often, which would use more fuel resulting in decreased fuel economy, such as the OP has. This could easily be checked with an app or VCDS to rule it out. Checking for regen frequency and soot and ash load as well.

For the OP to have such low fuel economy they either drive in such a way to ruin economy or something is wrong with the car.
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Old August 5th, 2019, 09:06   #19
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What size tires does your 2012 have and what pressure are they at?

If I remember correctly, the biggest the 2006 would have had would be a 205/55-16 where as the 2012 could have up to a 225/40-18. Increased width means increased drag.

Also, with tire pressures, most dealers inflate them to what the door label says for comfort. Which, I believe, is 35 psi.

If you pump that up to 40 it still rides fine, wears fine, and you get increased fuel mileage.
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Old August 5th, 2019, 14:53   #20
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To the earlier comment about the air filter, I checked it today, and while it is not brand new, it is clean and not clogged.

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Originally Posted by Fixmy59bug View Post
What size tires does your 2012 have and what pressure are they at?
They are 225/45-17. This is the "Premier" model, or whatever it was called, and it has the same size tires as my 2003 1.8T sport model had. I check them monthly and put them to the pressure listed in the door jamb, which I seem to recall is 33 psi, maybe it is 35.

Quote:
If you pump that up to 40 it still rides fine, wears fine, and you get increased fuel mileage.
I used to do that trick in my 1.8T: it said 30 up front and 28 in rear, and I ran them at 32 front and 30 rear. I should boost the pressure in these and see what happens.

I have a fuel filter swap scheduled for Thursday, and I will fill up immediately after that. Based on what the computer says (it is always 10% optimistic), I expect this tank to be around 25 mpg.

Thanks.
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Old August 6th, 2019, 06:46   #21
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For comparision purposes, the only valid test for fuel consumption is to do it the old fashioned way - miles divided by gallons consumed.
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Old August 6th, 2019, 06:55   #22
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Quote:
Originally Posted by scooperhsd View Post
For comparision purposes, the only valid test for fuel consumption is to do it the old fashioned way - miles divided by gallons consumed.
Absolutely, and that's what I do. In fact, I track with Fuelly.
However, I also track what the computer shows, and I have found it to be 10% optimistic. The computer currently shows 26.7 mpg for the tank, so I expect about about 24 mpg on this tank.
For comparison, here are my other cars: 2006 TDI and 2003 1.8T
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Old August 6th, 2019, 07:00   #23
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If only there was a sticky in the Fuel Economy section to read through. You know, like this one:

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

Yeah, that would be neat...
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Old August 6th, 2019, 07:07   #24
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Yeah, I read that a while back. Most of it I understand, and what of it I understand does not explain my car's FE.

It does bring up a question. I see references to different kinds of TDIs, "PD" for example. I know that PD stands for Pumpe Düse, but I don't know which engine code corresponds to my car. Unfortunately the relevant wiki page isn't much help to the neophyte. How do I figure out which one my car has?
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Old August 6th, 2019, 07:47   #25
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You have a "CR" family of engine, this simply denotes the type of fuel injection system, CommonRail.

VE came first, then PD, then CR, and now.... nothing [for us]
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Old August 6th, 2019, 08:42   #26
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Quote:
Originally Posted by oilhammer View Post
You have a "CR" family of engine, this simply denotes the type of fuel injection system, CommonRail.

VE came first, then PD, then CR, and now.... nothing [for us]
Thanks. I'm starting to understand that page a little more now. Looks like mine is one of the "2.0 R4 16v TDI CR" varieties, specifically probably one with one of the following ID codes, whatever that means: CFHC, CBEA, CBAB, CFFB, CBDB, CJAA.
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Old August 6th, 2019, 09:16   #27
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CJAA according to IDParts web site, which is a good source for this info to check up with as well as needed parts.
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Old August 6th, 2019, 09:24   #28
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Quote:
Originally Posted by Lightflyer1 View Post
CJAA according to IDParts web site, which is a good source for this info to check up with as well as needed parts.
Neat site - thanks!
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Old August 6th, 2019, 09:40   #29
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Yes, it is a CJAA.
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Old August 8th, 2019, 13:09   #30
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Got the fuel filter replaced today, and filled up immediately afterward. Computer said 26.3; real fuel economy was 24.5. It's probably my imagination, but the car seems faster than it was, and I could swear that the instantaneous fuel economy numbers shown on the computer are higher than they were. We'll find out in a few weeks when I next fill up, but I may be able to notice a different in tomorrow's commute. We'll see.
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