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Old 01-18-2012, 05:41 AM   #15
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Thanks guys. I was curious how it worked. I replaced the sending unit in my 87 last year, and until then, we used the pen and paper method. And I have to say we cut it REALLY close a couple of times. That's what prompted the replacement. I did notice though, that at 55mph I could get 9.5-10mpg (even towing the trailer with the 4 wheelers), around 60mph about 8mpg, and at 65mph only about 7mpg. I might add a vacuum gauge when I put in the trans temp gauge, just to have another "tool in the toolbox".
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Old 01-18-2012, 12:49 PM   #16
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Quote:
Originally Posted by LSC9901 View Post
Ahhhh yes. This what I was looking for. I knew something like this used to exist but I just couldn't remember what I was looking for. I guess my brain is now in the "Vintage" category also. I will just assume that the installation instructions a relatively clear. I'm not much of a mechanic although I'm always more than willing to jump in. Obviously with an '84 RV I've been initiated into the world of mechanics.

I've found all the parts needed at Advance Auto Parts for about $30. This includes the gauge, 6' of tubing and connectors and a gauge mount. It is the SunPro model. Has anyone else seen it for less anywhere? After all .... this whole thing is about conservation !!!

Thanks again for all the help ... as usual, everyone here is just fantastic.
Right now Amazon.com has the Equus 3620 Vacuum Gauge for $19.95 and the kit has everything you need to mount and tap into the existing vacuum system. The guage face is as close to the one I have as I can find so I know its easy to read.
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Old 01-18-2012, 01:51 PM   #17
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Easy to use and great tool.

Back in the day I used a vacuum guage for troubelshooting and adjustments.

Simply put, it measures the performance of the engine at all times.

The vacuum is created by the pistons doing their thing.

The faster the pistons move the higher the demand for air.

The relation to the opening of the fuel throttle plate is where the vacuum comes in.

If one floors it the plate is wide open, and as such there is ltiile to zero vacuum.

But as one is cruising the throttle plate will restrict the air flow, and a vacuum will be created, simple enough, but now it gets interesting.

If you have a "tired and heavy foot", say you just let it rest a little on the gas pedal, then the throttle opens just a tiny bit, this lowers the vacuum, allows more air flow which allows more fuel to go in.

If it is just a tiny bit the difference in real power may not be enough to notice or even change the speed, but the fuel consumption will go up a bunch.

So the result is to determine the magic number at any given speed, say at 60 MPH on flat land the number should be 17, if you are at 16 too much gas, at 18 you loose speed then need to gain the speed back.

So driving by the vacuum guage will allow you to find the sweet spot at any given load or speed.

You also can learn the maximum amount of gas to use at any given time, as you push the pedal the vacuum drops, at a certian point the drop will be steep and the power gain little at that point.

You can determine the sweet spot for take off as there is a certin amount of pedal that will be the optimum amount of power where any more just dumps the fuel through the engine.

Next, you will learn the habits of your engine, if the engine gets a clogged air filter, bad injector or other problem the sweet spot that was say 17 now will be 15, this change indicates you need to investigate.

Bigger number is better.

Check out OLD SCHOOL text books on autos, they will have many tips on how to use the guage.
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Old 01-18-2012, 09:30 PM   #18
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Right now Amazon.com has the Equus 3620 Vacuum Gauge for $19.95 and the kit has everything you need to mount and tap into the existing vacuum system. The guage face is as close to the one I have as I can find so I know its easy to read.
While this one is cheaper it also appears to be a test gauge. For the few extra dollars I'll get one that can be permanently mounted. I can get what I need for $24.48 plus tax. Now I just need a boost of confidence to install it. Does that come in 12 OZ bottles?
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Old 01-18-2012, 11:23 PM   #19
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This is what you really want. It is called the Autocomp 8000 but unfortunately, it isn't made anymore. It connects to the fuel line and speedometer cable and computes mpg and fuel flow among some other things. This one was found on eBay a couple of years ago. They were made back in the late 70's and 80's.





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Old 01-19-2012, 05:13 PM   #20
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Don't waste your money. Use the old paper and pencil. I have a vacumn gauge on my 87 Allegro and it isn't even close. Anything that is added (gauges, especially to an older vehicle) is a waste of money. Go fill up and drive it in some different environments and then track you mileage. Its how we did it before computers. Still works today. Even though my SUV has all the bells and whistles I use the math.

Good Luck
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I think you misunderstand my goal. I already use the pencil & paper method. What I'm looking to accomplish is merely see a visual readout of when I have to much foot into the gas. We all, or should anyway, that starting from a stop is when gas consumption rises and most of us that care are aware that at speeds in excess of 55 decrease MPG's. I just want visual assurance that at 58 MPH's I am using more fuel that at 55 MPH's or whatever is the optimal speed for my RV. I already know that at 70 MPH's my consumption will be higher. I know what my basic MPG is and I know that each trip it will vary just due to different elevations, temps and so on. Just looking for what is happening at any given moment versus the long term. If i behave then the long term should be just fine.
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Old 01-20-2012, 09:42 AM   #21
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When I was in high school or shortly after but I think in school, (Class of 1968) I recall reading in Popular Mechanics about a new computer that you could install. It had a sensor that "Spliced" into the speedometer cable, and another that "Spliced" into the gas line, and a few other things. it accurately measured distance traveled and fuel consumed and did the math.

Alas, that is about all I recall about it. Google may find it, if it's still made.

By the way. I have not given away my age.
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Old 01-27-2012, 03:54 PM   #22
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Hey All,

I have a Motorhome with a Chrysler Industrial TBI 360 V8 (5.9L) I have a gear vendors over/underive that I can get speed pulses from and I can tap an injector (I have 2) for pulses there. It has the old Chrysler spec OBD1 so Scangauge is out. It's got Throttle Body Fuel Injection.

I have an MPGuino built (though I am still puzzling out an enclosure to sit on the dash)

While browsing online I cam across a vintage Trip computer/mpg meter called an AUTOCOMP. It has a fuel flow sensor and may be able to get speed signals from various inputs. It's designed for carbureted engines.

It isn't specific about Throttle Body Fuel injection. I believe it will work with my setup, but am unsure. A regular high pressure system with rails, etc would likely burst something important, but my fuel pressure is much lower.

What do you all think??

Also, anyone actually have one of these?? I'd buy one if it would work...

Were there any other similar devices that would work with my drivetrain???

Thanks,

Rich "The Wanderman"
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Old 01-27-2012, 06:48 PM   #23
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Quote:
Originally Posted by Wanderman
Hey All,

I have a Motorhome with a Chrysler Industrial TBI 360 V8 (5.9L) I have a gear vendors over/underive that I can get speed pulses from and I can tap an injector (I have 2) for pulses there. It has the old Chrysler spec OBD1 so Scangauge is out. It's got Throttle Body Fuel Injection.

I have an MPGuino built (though I am still puzzling out an enclosure to sit on the dash)

While browsing online I cam across a vintage Trip computer/mpg meter called an AUTOCOMP. It has a fuel flow sensor and may be able to get speed signals from various inputs. It's designed for carbureted engines.

It isn't specific about Throttle Body Fuel injection. I believe it will work with my setup, but am unsure. A regular high pressure system with rails, etc would likely burst something important, but my fuel pressure is much lower.

What do you all think??

Also, anyone actually have one of these?? I'd buy one if it would work...

Were there any other similar devices that would work with my drivetrain???

Thanks,

Rich "The Wanderman"
What year is yer motorhome? I didn't realize there was much of anything from Chrysler on terms of eve past the late 70s early 80s.

My truck has the 360-1 tbi engine, but it's a 92.
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Old 01-27-2012, 07:51 PM   #24
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RV.Net Open Roads Forum: The old girl is back - where to start

This is a long old thread on rv.net that shows the installation of an AutoComp8000B. This is page 45 of 87. On page 43 he shows the package as he got it from eBay. This was a long refurbishment of an old Monaco that is a pretty good read if you have the time. There are a lot of good ideas, and some not so good, but food for thought.
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Old 01-27-2012, 08:06 PM   #25
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My RV is a 1991 Aero cruiser. It has a Chrysler Industrial modified by the manufacturer LGS Chassis with a 1989/90 Chrysler Industrial 5.9L TBI motor (360 V8)

Mostly Dodge 1 Ton 4000lb axle with a heckuva a lot of modifications.

I talk a lot about it in my articles.

The Autocomp thread was great info. Though no one seems to be able to tell me if I can use VSS or some other way to get speed reference other than their supplied adapter.

I also have Throttle Body Fuel Injection...around 20psi or lower so I am unsure the flow sensor would be OK...

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Old 01-27-2012, 08:14 PM   #26
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Originally Posted by Wanderman View Post
My RV is a 1991 Aero cruiser. It has a Chrysler Industrial modified by the manufacturer LGS Chassis with a 1989/90 Chrysler Industrial 5.9L TBI motor (360 V8)

Mostly Dodge 1 Ton 4000lb axle with a heckuva a lot of modifications.

I talk a lot about it in my articles.

The Autocomp thread was great info. Though no one seems to be able to tell me if I can use VSS or some other way to get speed reference other than their supplied adapter.

I also have Throttle Body Fuel Injection...around 20psi or lower so I am unsure the flow sensor would be OK...

Rich "The Wanderman"
Oh, likely less than that given that the intank Carter fuel pumps only put out an at max 18PSI, and the diaphragm that regulates the pressure in the Holley TBI usually opens up around 15 PSI to return excess fuel back to the tank again.

However, having said all that, I think most carb systems run at around 5-10 psi.
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Old 01-31-2012, 06:49 PM   #27
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What I'm looking to accomplish is merely see a visual readout of when I have to much foot into the gas . . . . I just want visual assurance that at 58 MPH's I am using more fuel that at 55 MPH's or whatever is the optimal speed for my RV . . . . Just looking for what is happening at any given moment versus the long term.
The question has been answered. With a tachometer and a vacuum gauge (a quality pair, such as from AUTOMETER). Be sure to correct for tire size and any speedo/odo discrepancies (GPS is handy for both of these, and manufacturer speedo gear charts to get you closer to optimum) which should be entered into any calculations.

Besides, you will always use more fuel at 58-mph than at 55-mph all other things being the same. When they aren't, the above two gauges will reflect that.

Travel speed is only one gauge of steady-state fuel economy. Number of steering corrections per 100 miles is another, as are braking applications over the same. Then there are the variables of climate, terrain, weather, traffic and driver skill.

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Old 02-01-2012, 05:21 PM   #28
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Additional thoughts
Others have stated using the tach with vacuum.

That brought up something else.

The peak torque and horse power are at specific places on the tach.

If one is traveling just a little bit slow, say 50 and they are just under the optimum torque range the engine may be lugging, using more fuel than say running at 55.

The greater speed alone is not going to cause worse fuel mileage, it is a contributing factor.

If you want to do some homework you could look up the specifications of your drive train to determine the optimum speed via gear ratios and tire sizes.

This will be where the engine torque and horsepower are optimum, the racing guys can better advise how to interpet the data.

Now we use a made up number of 55 MPH as the optimum, head wind or drag will impart additional loads on the engine, so difference from 53 to 55 not much, but torque maybe so.

Now you use the vacuum guage, and to determine the best operation you do NOT want any of the slap under the dash ones, they are too small to see and do not have the resolution you want.

Go to the supply store and you will see large ones for testing vacuum and fuel pump pressure, they are more accurate and it is easy to read small differences.

You wil need to lay it on the doghouse, but so what.

Now you go out on a long flat road and look for the sweet spot, you are looking for the highest vacuum near the optimum speed.

You will observe the vacuum will remain in a small range while cruising across a wide range of speeds with the cruise control on.

As you slowly increase speed there will be a certian speed where the vacuum drops off, this is the speed for which you have exceeded the cruising torque of the engine.

What I mean here is think about cruising down the highway, foot on the gas at a certian spot and all is well, when an overpass arrives you need to give additional fuel to provide the power to get over the hill.

When you are cruising down the road you engine is running under a certian load, as your speed increases the RPM of the engine increases to drive the vehicle at that speed, and the foot applies enough pressure to supply the correct amount of fuel for the given RPM.

As the speed increases the wind resistance also increases, at some point it will overcome the normal output of the engine at the given RPM and require more fuel, just like the overpass.

The vacuum guage will show you where that point is as the vacuum will drop fast when you get there.

Once you have your sweet spot found, then the small guage is fine as for normal driving you just want to drive for peak vacuum, you already know your maximum cruising speed.
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