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Old 08-04-2007, 09:39 AM   #41
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You should fill your tank up right before and right after your vehicle gets repaired.
I wish that had occurred to me. I did keep track of the distance they test-drove the car, though.

Got a little surprise... I unplugged my ScanGauge and took it with me (since they would be using their scanner, plus I didn't want them playing around with my SG and maybe clearing some figures). Unfortunately, while it remembered my mileage and gas figures over the course of the day, it forgot everything else (engine displacement, tank size, etc.)

I think I got everything set back as it was, but FE seemed unusually good on the way home (won't know for sure until I drive one of my regular routes). Maybe it was my imagination, maybe the SG calibration is still off, or maybe the oil change and other maintenance are helping things run more efficiently. (Others say their numbers go up right after an oil change.) We'll find out on the next tank fill, but it looks like there's yet another variable in the mix.

Rick
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Old 08-04-2007, 10:21 AM   #42
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RR,

If they actually replaced "timing belt/tensioner/water pump" then heck yeah you will see way better gas mileage! Were you seeing more than a "2LOD" load on your scangauge at engine idle before repair, and where does it sit now?
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Old 08-04-2007, 12:11 PM   #43
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If they actually replaced "timing belt/tensioner/water pump" then heck yeah you will see way better gas mileage!
Help me understand the "why" of that, Will?

Yes, they did. The damper was also replaced.

Quote:
Were you seeing more than a "2LOD" load on your scangauge at engine idle before repair, and where does it sit now?
I try to avoid idling but I believe the load at idle was 2 or 3. I tend to swap TPS and LOD depending on what I'm playing with at the moment; it was set to TPS on the way home from the shop and I haven't driven the car since.

It did seem to want to idle faster than before -- normally I see something in the mid- to high-800s, and yesterday I saw some 900s. I wondered at the time if that could be the result of less mechanical load with the same fuel feed or an adjustment they made. I presume the ECU controls idle RPMs, in which case the latter would make more sense.

Note that, since starting to hypermile, I've been getting to and from the city during off hours on roads with a 40MPH limit maximum. Coming back from the dealer yesterday, I had to drive mostly on 65MPH interstates in rush-hour traffic. The slowest I was able to get down to was maybe 55 once or twice. So I won't know for sure about a change until Tuesday when I again drive my normal work route.

The timing of this is unfortunate but not a killer, since I can always establish a new baseline and from that come up with an adjustment factor.

I'm definitely not going to complain about anything that gets me better FE, regardless of the timing!

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Old 08-05-2007, 07:57 AM   #44
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Rick,

Old timing belts get hard, brittle or begin fraying and all that increases friction. Water pumps and tensioners have bearings, and as they age that bearing loses its ability to freely rotate.

So with you getting those replaced, your engine is definately spinning more freely due to less friction inside the belt system and inside the timing system!

And yes you will see increased RPMs after all that work simply because the Tech's unplugged your battery to work on the car, and the ECU is "re-learning" where it can efficiently idle at.
I'll bet your LOD was 3, and now its going to be 2.

The other benefit to getting the timing belt replaced is now your timing is more exact than with the old stretched belt. That will also give you some increased efficiency.
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Old 08-05-2007, 11:35 AM   #45
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Old timing belts get hard, brittle or begin fraying and all that increases friction. Water pumps and tensioners have bearings, and as they age that bearing loses its ability to freely rotate.

So with you getting those replaced, your engine is definately spinning more freely due to less friction inside the belt system and inside the timing system!

The other benefit to getting the timing belt replaced is now your timing is more exact than with the old stretched belt. That will also give you some increased efficiency.
Makes sense. Thanks!

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And yes you will see increased RPMs after all that work simply because the Tech's unplugged your battery to work on the car...
Ah crud, I completely forgot about that. Ironic; I was careful not to disconnect the battery when pulling/replacing my instrument cluster so as not to disturb the ECU, and as soon as I get the cluster re-installed I take it to the shop so they can do it. D'OH!

Seems odd, though: I'd have thought losing the mappings would cause FE to go down.

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I'll bet your LOD was 3, and now its going to be 2.
I had to take a short drive this morning -- idle load was at 3. Also, idle RPMs were back in the mid- to upper-800s again.

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Old 08-06-2007, 04:40 PM   #46
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First Shell mid-grade segment complete; 33.92MPG over 308 miles. There are entirely too many variables to make any assumptions at this point, so I'll wait for trends to emerge.

Rick

P.S. The odometer ran lower than the GPSr by about 2%. This is a relatively small error, equaling only 1/2 MPG or so.
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Old 08-07-2007, 10:17 AM   #47
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Rick,

Quote:
I had to take a short drive this morning -- idle load was at 3. Also, idle RPMs were back in the mid- to upper-800s again.
I'm not sure if the fuel map was reset, but I do know that the route the ecu takes and under which conditions getting to "target idle" was reset.

And when I spoke of the idle load, I should have noted that 2 will be when fully warmed. I think that has to do with the warmth of the serpentine belt and ring seals...after running for so long, belt becomes more plyable and the rings seal the energy better then the lod decreases.

And if you made more than 4 turns in your short commute, I would trust the odometer over GPSr. And I agree on waiting for trends to emerge for your FE.
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Old 08-12-2007, 06:19 PM   #48
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Second Shell mid-grade segment complete; 33.75MPG over 349 miles. This is very consistent with the first mid-grade tank. I refilled with mid-grade again to see if continues to be repeatable.

I rechecked the odometer/GPSr calibration, and again saw approximately a 2% error (about 1/2 MPG over a tank).

My impression of getting better FE post-service was apparently due to the ScanGauge losing its tank-fill adjustment factor. Gallons were low on the first post-service fill and adjusted; on this fill the reading was once again low and about a 4% offset was required. On this tank I'll probably see MPG numbers more in line with what I was used to seeing. (Note that these misleading numbers had no bearing on the VW's gaslog or the numbers reported here -- those come directly from odo mileage and gallons pumped.)

Rick
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Old 08-15-2007, 04:59 PM   #49
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Third Shell mid-grade segment complete; 35.54MPG over 378 miles. I pretty much screwed up the test series with this tank. First, I had to make a fairly long trip on a road that was absolutely perfect for high-FE driving, and I took full advantage of it.

Then, since I knew the numbers would be off anyway, I installed an upper grille block and front air dam about halfway through the tank.

I'll continue forward with the test then go back and re-baseline everything. I'm hopeful that, by then, my driving style will have settled in pretty well and any variances in Shell V-Power versus other Shell gas grades versus random gas will be more visible.

Also, if there's a strong discontinuity from this tank forward, it might still be possible to subtract out that offset and see other trends.

Rick
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Old 08-20-2007, 04:49 PM   #50
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Fourth Shell mid-grade segment complete; 35.46MPG over 331 miles.

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