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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 12th, 2017, 18:05   #1
Join Date: May 2009
Location: Berkeley, CA
Default 2 mile/gal projected loss of fuel economy with "modification" of 2009 Jetta why?

Subj: 2 mile/gal projected loss of fuel economy with "modification" of 2009 Jetta why?
related Subj: "modification" vs "buyback" 2009 Jetta TDI Sportwagon

I just received a "recall" package describing the "modification" for my 2009 Jetta TDI Sportwagon located here in California. The package describes the proposed "modification" as reducing fuel economy by 2 miles/gallon and I'd be interested in any engineering assessments about what exactly the "modification" fix does that reduces fuel economy and performance.

Also of interest although not directly related to fuel economy, VWcourtsettlement.com is reporting they will pay $21,136.73 if I return it on 4/2/2018 or if I do the "modification" on that same date a payment of $6011.73 but the "modification" is described as reducing fuel economy by an estimated 2 miles per gallon and also effecting engine noise and performance. I'm considering 4/2/2018 because that is the month the registration will be due along with a CA required "smog test" that I am presuming would be failed without the "modification." An earlier "modification" or "buyback" date 8/26/2017 results in a smaller restitution payment of $5906.73 for "modification" and $20506.73 for "buyback." So it seems like it is better to delay until shortly before the required "smog" test.
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Old August 12th, 2017, 21:53   #2
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Join Date: Dec 2012
Location: Chicago

My understanding is that part of the fix is a bigger nitrogen oxide storage converter, and that the fixed software will refresh that converter more often, by injecting extra fuel to reduce the stored nitrogen oxide to nitrogen. So the car uses more fuel than before to put out less NOx, at the price of putting out more CO2. You pick your poison (or rather, the EPA picked it for you).

If it works, take it apart and find out why!
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Old August 13th, 2017, 03:31   #3
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Join Date: Aug 2004
Location: South of Boston
Fuel Economy: 50/45/37

I don't think anyone will know for sure the cause of the FE loss until cars are fixed and folks get to see the hardware and software changes. But I bet the loss is from fueling map changes, retarded timing to reduce NOx, and more after combustion dosing to improve the operation of the DPF and Cat. But that's my guess. Honestly, I don't think the number is that significant. Again, we'll know better once some fixed cars are out there accumulating miles.
2002 Jetta wagon, 351K, RC3+; 1993 Mercedes-Benz 300D 2.5, 197K; 1997 Passat, 283K; '99.5 Golf, 255K; 2011 335d, 52K; 2015 Golf Sportwagen, 2K. Principal, http://www.idparts.com
Kid's cars: 2002 Golf TDI, 2002 Jetta TDI
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