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Old 10-09-2008, 12:39 AM   #1 (permalink)
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n00b here- 2001 Jetta TDI

Hello-
I'm a 2001 TDI Jetta owner looking to squeek a bit more efficiency for my 22 mile round trip commute. I run B20 and just ordered a ScanGuage II from JCWhitney for $159.99 with free shipping and a $50 JCWitney giftcertificate.
I need to read up on many things but I think I'm going to start with tire pressure, driving habits, and possibly blocking off some of my air intakes. This site seems like an excellent resource.

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Old 10-09-2008, 08:44 AM   #2 (permalink)
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Schwartzejetta - '00 Volkswagen Jetta TDI GL
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Welcome aboard!

You've the same body style as me, only a year younger. Is your car automatic, or manual?

What you're aiming for is prudent.

Driving style, you'll be able to monitor better with the Scanguage.

Some of the driving styles advocated here are more relavant to gas engines than diesels. The modern electronic injection diesels, like the TDI, will stop pumping fuel when you are off-throttle coasting down stops, or down inclines. That's free savings there, until your engine drops closer to idle speed - 1200rpm and lower for the TDI, it'll start fueling the engine to maintain engine speed. If you're not doing it already, use this to your advantage, it's a freebie.

From my own experience, TDI engines seem somewhat prone to air issues. Namely, keep...
  • the snowscreen on the air filter clean
  • the air filter clean (depends on how dusty it is, for me)
  • the MAF (Mass Air Fuel) sensor is operating correctly so you get accurate readings

Even with a bad MAF sensor, I've still been able to get good mileage, but highway omph is lacking when the ECU uses it's backup fueling pattern and goes into "Limp" mode.

And, with the nature of the little diesel, engine tempurature (coolant temp) will also affect mileage. This, and winterized diesel is a big factor with short drives in the winter months.

Between MAF sensor issues and me having trouble keeping a consistant fuel point, my SG readings tend to fluctuate from pump receipts and my trip odometer readings, so, don't be too alarmed by that. Use it as a tool to figure out relative efficencies on your usual commute, until your ScanGauge is calibrated.
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Old 10-09-2008, 09:39 AM   #3 (permalink)
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Thanks for the info ChrstphrR.

I forgot to include my trans in the description- I have a 5 speed manual.
I have new MAF after spending a week or so in "limp" mode about seven months ago.

Can you tell me a bit more about " off-throttle coasting down stops, or down inclines"? I assume this means leaving the clutch engaged and letting off the throttle. I'll search for diesel driving tip threads for more relevant info my TDI.

I guess its time to invest in a manual for this car. I used to have a pdf of it but lost it in a bad hard drive failure.
Thanks again for the info.
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Old 10-09-2008, 09:41 AM   #4 (permalink)
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Hey sharpfork! Welcome to ecomodder. Don't forget to fill out a garage and fuel log and such.
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Old 10-09-2008, 10:51 PM   #5 (permalink)
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Schwartzejetta - '00 Volkswagen Jetta TDI GL
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Quote:
Originally Posted by sharpfork View Post
Thanks for the info ChrstphrR.
Can you tell me a bit more about " off-throttle coasting down stops, or down inclines"? I assume this means leaving the clutch engaged and letting off the throttle. I'll search for diesel driving tip threads for more relevant info my TDI.
I haven't looked in my driver's manual to see if it mentioned this tidbit -- it's something I'd picked up reading at TDIclub's forums years ago, when researching the TDI diesel when I was looking for a newish car.

This is one of many from that forum that give a bit of a description about the phenomenon, without being overly technical.
Please explain how my car uses NO fuel while in gear coasting downhill?? - TDIClub Forums

Synopsis: When coasting down In Gear, not neutral nor with the clutch depressed, the engine computer knows to shut off the fuel flow, as long as the engine speed is above 1200 rpm. While in gear, the momentum of the car moving / the drivetrain/transmission spinning is enough to keep the engine moving, until that 1200rpm point.

Not to detract from this forum in the least, but since you do have a TDI, make sure you use that resource too, if you haven't already. Like Ecomodder, it has a pretty knowledgable and welcoming community... and close to 10 years of information about our particular car and engine type. Since both car and engine maintenance are pillars of good fuel economy, it's good to use the tools available to help you achieve better fuel economy.
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Old 10-10-2008, 03:25 AM   #6 (permalink)
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It's called injector shut off. I also recommend checking out tdiclub.com. They have a whole section dedicated to what you are asking about. Also not saying to disregard this forum, but use tdiclub for your diesel and TDi specific questions.
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Old 10-13-2008, 02:36 AM   #7 (permalink)
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Thanks a ton for the info. For a TDI owner, it seems like ecomodder is a great site for general knowledge as well as a good place to point my gas burning friends to. For TDI specific info, I'll be spending lots of time reading the TDIclub Fuel Economy forums.
My ScanGuage II should be waiting for me when I get home from work tomorrow. I haven't even started with hardware and I'm already trying to figure out how I might be able to integrate a touch screen PC running vag-com into my car.

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