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Old 06-28-2010, 01:02 AM   #1 (permalink)
OldertechGuy
 
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Mountain driving with Honda VX

We just got back from the mountains of Colorado. With no MPG reading devices, I'm wondering... I know that coasting in idle is a way to make maximum efficiency down hills, but when the hills are mountains, you have to stay in a gear to hold the car from going too fast, and not burning up your brakes.

My question: Coasting down a mountain in gear in a '92 VX - are you burning gas? Or is gas shut off to the injectors if no power is needed?

As it was, we got 47 MPG driving home to Kansas at 75 MPH with AC on a lot of the way. Sure need to add a MPG computer to know what it really is doing all the time.

Scott

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Old 06-28-2010, 01:14 AM   #2 (permalink)
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If you're engine braking you will not be using gas.

Have you thought about picking up an MPGuino yet?
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Old 06-28-2010, 02:11 AM   #3 (permalink)
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you can feel the deceleration fuel cut off. As you are coasting down in gear with (3rd is shows up well in the honda) as you get down to about 1000 rpm you will feel the decelration from the engine braking stop. you can pick up a replacement instrument cluster with a tach for 30 bucks from a u pick a part, and install a wire off the speedo when you install it for the mpguino. It literaly takes less than 1 hour to both. Assuming you have a 5th gen honda.
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Old 06-28-2010, 07:33 AM   #4 (permalink)
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Considering the average speed and AC use, I would consider 47 MPG to be about the optimum mileage you would get.

I would probably get about the same around here where it's fairly flat.

With AC on fuel shut off is about 1200 RPM, so you want to use the proper gear to maintain your downhill speed. Probably 4th or 5th depending on the grade.

When climbing you can stay in lean burn if you can maintain a manifold vacuum of over 5 inches. On grades that require downshifting for the down slope, the corresponding up slope would be difficult to climb at any decent speed while maintaining 6 inches of vac.

I would say the major factor in your mileage was your high average speed, much more so than the grades you encountered.

PS VX had a factory tach.

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Mech
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Old 06-28-2010, 09:47 AM   #5 (permalink)
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MPGuino

Sure have thought about MPGuino. Where do I get one and where is the most comprehensive info on how to install/use?

Scott
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Old 06-28-2010, 06:56 PM   #6 (permalink)
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That funky gas tank

The prime reason I'd like a mileage computer is that gas tank. For a car that is so carefully thought out to get high mileage, the regular means of checking, by dividing the gallons filled by the mileage driving is really, really hard to consistently do. If you stop filling the tank as soon as the pump clicks off, you are short about 2 gallons. If you trickle, trickle, trickle, you can go to a place that I named, "hyperfill." When I "hyperfill" the tank, I can go 200+ miles before the gauge drops from F.

I've looked at the tank design and it seems the filler tube is below the top of the tank. So when we trickle, we are kind of forcing fuel into the expansion area? Has anyone else acknowledge this in the VX? We had a Del Sol, and never had wacky filling issues.

By the way, I've read that the '92 VX has a 12 gallon tank, and the '93-'95 has a 10 gallon tank. Can anyone verify that?

Scott
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Old 06-28-2010, 07:03 PM   #7 (permalink)
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I can verify that my '94 has a 10 gallon tank, according to the manual that came with.
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Old 07-07-2010, 02:59 AM   #8 (permalink)
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Quote:
Originally Posted by oldertech View Post
Sure have thought about MPGuino. Where do I get one and where is the most comprehensive info on how to install/use?

Scott
http://opengauge.org/mpguino/

The install is pretty easy, there are a few of us using them in 5th gen civics, the install is pretty painless. If you require a bit of guidance just do a search in the DIY or instrumentation forums or ask.


in my DX filling to the first click, I can go about 150 miles (50+mpg) before I come off the full mark. The tank 11.9 gallons. the first 3 gallons gets it off the full mark. The next 3 brings it to the half way point. 3 more drops it to the empty mark. and the last three just about on E to sputter.
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Last edited by bestclimb; 07-07-2010 at 03:19 AM..
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Old 07-07-2010, 06:47 AM   #9 (permalink)
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I cut a piece of 2X4 with a angled edge. When I pull up to the pump I drop it in front of the left rear tire, and raise that end up slightly.

Consistent fill ups and about 50-60 miles range to the same point on the gauge when it gets to about 400 miles on the odometer.

One day I will carry some extra fuel and run it out to see what the gauge reads, but the way the needle oscillates, you can probably get a pretty good idea when it stops moving altogether. I think one time I got over 9 gallons in it but I don't like to run in tank electric fuel pumps dry. In my opinion since they are cooled by the fuel, it could shorten the life of the pump.

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Mech
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Old 05-05-2015, 11:55 AM   #10 (permalink)
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Found this thread trying to figure out how the tank is shaped and how the gas is measured.
The gauge drives me nuts. First because of the way it drops at a certain point when you think it's getting better mileage and then you have to wait for the drop. Why?

In the recent past I knew I was getting 47 plus mpgs regularly when the needle was just above halfway or roughly 200 miles. I've been having trouble achieving that mpg after lots of major maintenance and so have been watching the needle very closely.

Also, does it make sense that the car should hesitate when the tank is less than a quarter full? I've been encouraged to get the best mpg evaluation, run the full tank. I was filling up at a Shell station (using 85 octane-bad or good BTY) but I started getting short fills and splash overs. This has happened at another station. I switched to a small corner store to support a local business and liked the pump but I think the gas was bad.

I thought that gas might be the cause of a hesitation I feel right about where you want to shift (2000 rpm unless I need to get going). That Seemed to make a difference in power, my mpgs looked great on a highway trip at 60 mph from Denver to Colorado Springs. I really wanted to fill up after the first 100 miles because the needle barely budged, but resisted. It will be a good tank since I'm around 350 now and I feel like I'm right above that last darn drop on the gauge.
But now even with the better gas, the hesitation is evident to me again at least (my mechanic can't feel it when he drives it).
Any idea if gas level can make the engine hesitate?

I finally found a Conoco that bubbles up so I can hear it then the pump automatically stops. That will be my pump for three tanks.

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