- Joined Sep 24, 2015
I have an old MAP sensor (Manifold Absolute Pressure) sensor that has three pins "+5V…Vout…Gnd" I've pierced the back side of the MAP sensor to measure air pressure.
That's why I've pierced the back side. I've tested the output on my scope by blowing air into the opening I created. It works.The MAP Sensor is designed to measure between ambient Atmospheric-Pressure, and MINUS (roughly) 12 PSI, ( close to a Vacuum). It is not designed to measure Pressures in excess of Atmospheric-Pressure.
Actually, a MAF could work as well.As LowQCab points out , its really a MAF , Mass Air Flow sensor, normally mounted pre carb' input to measure air intake vacuum level, for fuel control.
This I know. However, there's a fundamental difference between a MAP and a MAF."In fuel-injected automotive engines, a manifold absolute pressure (MAP) sensor is used to continuously monitor the amount of air flowing into the engine, so the computer can calculate air density, adjust the amount of fuel to spray into the combustion chamber and adjust the ignition timing. In some vehicles, a mass air flow (MAF) sensor is used. While the two are interchangeable, a MAF sensor measures flow rather than density."
Again, this is something I'm well aware of. Which is why I want to know in real time what the effects of another vehicle are. As some are suggesting, using the fuel gauge doesn't provide the real time feedback I'm looking for. Yes, hills, gusts of atmosphere (wind), tire air pressure, all conspire to create an overall picture of performance. It's not the overall I'm looking for - it's the moment by moment indication of how another vehicle is affecting my vehicle.The Aerodynamic-Drag on the Body of the Truck can fluctuate wildly,
depending upon the constantly changing environment, and Speed.
Doesn't have to be a computer fan. I have a bunch of DC motors scrapped out of old tape decks and other odd sources of motorification.I initially suggested the computer fan but then deleted my post thinking that you already had a MAP sensor. I was not sure if the fan would give you any voltage if spun by air.
I thought of this but building the Venturi means having an exit point for the airflow, which can change how things look.If you put your MAP sensor inlet in the side of a venturi, you will get a vacuum reading as air goes thru the venturi.
The available data via the mileage indicator is not sensitive enough to give me the real time indication of what's going on.It is obvious that tailing will benefit, but method described here doesn't provide any measurable data for such purpose.
The most simple way without any additional sensors is to measure your real time fuel consumption to tell how much less it takes to go the same speed behind another vehicle.
On the same road day after day mileage can vary from many factors. Traffic, speed, headwind versus tail wind or cross wind etc. all can change the reading. So I get an average readout by the end of the tank, which can indicate that during the last few weeks I encountered several differing factors that came into play for fuel economy.
I'm not looking for a way to increase gas mileage. It is what it is. I'm most curious about the effects of another vehicle directly in front of me. Not looking for "Meaningful" data, just a fun way of indicating what happens when you ride behind a big rig. Yes, I know I will get better mileage. But often times there's a cross wind which can drift the vacuum behind the rig to the side. If you're not in the vacuum you're not benefiting from it. Sometimes just sitting off to the side can be of benefit. Knowing where the air is going likewise helps to "Know" this. Benefiting from the knowledge is a different thing.
Again, accuracy be damned. This isn't a serious project, just an elementary school science project. Like what happens when you mix red and yellow food coloring in a cup of clear water. Just something for me to do besides going in the woodshop and sanding yet more drywall mud, then having a ton of baby powder all over everything in the shop. Yesterday I cut some wood for the railings around my deck. Today I'm going to be nailing those pieces so I can pass inspection (whenever that happens before mid October).