new or used air filter makes no difference on MPG

[sdowney717]

seeing the closed loop injection cycle when it finds less air, will lower the injected gasoline volume to keep the mix stoichiometric. You would think less gas would mean a better fuel economy? Perhaps not seeing the engine power output will go down with less air and less fuel. Still would it not improve highway mileage a tiny bit to have a restricted air supply?

I did find when my in tank fuel pump was failing and the pressure dropping, that my mileage jumped up 3 or 4 mpg.

One symptom of that is you have no revability at highway speeds, your car can get up to speed slowly. Acceleration causes backfiring due to the mixture being lean.
I was thinking if you lower your pump pressure by lowering the voltage then it would do the same result as a weak fuel pump.
Lean mixtures might cause engine piston damage due to less cooling effect of a proper charge of gasoline which absorbs cylinder heat when injected, lean burn makes engine better mpg, less power, water temp stays the same.

Still I was thinking of a variable resister in the pump power circuit and see what happens.

Quote:

the US EPA and IATn have conducted pretty thorough testing which shows that up to about 50% restriction of the air filter has about zero effect on fuel economy On Fuel Injected systems , it does reduce maximum flow and so will reduce maximum power output -

these tests were in response to the many false claims of various vendors including but not limited to K & N that replacing air filters could somehow magically improve fuel economy

it does not
as demonstrated by the test results in at least 3 separate sets of testing

http://ecomodder.com/forum/showthread.php/air-intake-restrictor-b-test-19054-2.html

 

[NHGUY]

How about an adjustable pressure regulator? If you could get one that was dashboard adjustable you could crank the psi down around town and idling,crank it up at high speeds (65+)??

 

[sdowney717]

fuel pressure setting is designed to get max power out of an engine. The car with bad pump is a 94 Buick Roadmaster with LT1 MPFI engine. Lets say your able to lean mix when engine power demand is low, like after it has gotten up to speed and just cruising. Perhaps even rig this so pump pressure is modified engine vacuum.
High vacuum engine load light, lower vacuum engine load heavier.

 

[The_Jeff]

You would have to rig it so you'd get it to operate just outside of the adjustable section of the closed loop programming, but without running so lean as to burn a valve. Probably the best way to do so would be a permanent open loop status, and a piggyback on the MAF sensor reading.

Look at GM's "highway mode" of a 17:1 AFR circa 1990. They got busted on this and had to reflash PROMs to eliminate it. You could get a custom chip, back when they were chips and not software flashes, that re-enable said "highway mode". If I were to guess how they got away with it (for a while), it kicked in at 56 MPH which was above the speed limit of the day, (or at least where they certified the car) but factually where many people drove.

They had to get rid of it because of high NOx emissions.

A variable resistor better be big, the pump draws lots of power. Plug you might blow the pump motor with low voltage. I like the adjustable FPR idea better.

I suggest you read up on your theory more before you blow up expensive parts of your car.

 

[gathermewool]

Emissisons!!!

My fuel pump is multi-duty-cycle, based on requested torque, IIRC. Not sure which other models are.

Also, detonation will be an issue, as well as EGT's. Lastly, an extremely dirty filter may help MPG's due to forced lower performanc, but it will increase pumping losses, those losses associated with actually sucking in the air/fuel and pushing it out as exhaust.

 

[Jim Allen]

The increase in economy is likely due to less throttle being used, since more resuted in problems. You could achieve the same thing by just driving the way to were driving with the bad pump.

Higher pressure results in better atomization (and more flow too if the pulse width is increasesed). With low pressure, the PCM is compensating by increasing the pulse width on the injector to get the required mixture and the fuel is less well atomized. Some custom programmers will tune to get the pressure up at every level to increase atomization and fuel economy.

 

[sdowney717]

The car was like a dog trying to get going.
your partly right as I could not give it much gas pedal. Mostly noticed too much pedal gave no power and way too much pedal it would backfire and bog.
I have tried driving the car with a very light pedal and noticed little or no improvement in MPG.

As far a pressure atomization, I think that is a false thinking trap. the engine downstroke is creating a suction and engine heat will vaporize the fuel. It is still being injected as small droplets even with the lower pressure or it wont run at all. Perhaps not as efficiently.

I am thinking just enough pressure drop under light cruise conditions to improve mpg. If intake vlave burning or piston dome overheating then think about water vapor injection as an aid to keep it cooler.

 

[Jim Allen]

Originally Posted By: sdowney717


As far a pressure atomization, I think that is a false thinking trap. the engine downstroke is creating a suction and engine heat will vaporize the fuel. It is still being injected as small droplets even with the lower pressure or it wont run at all. Perhaps not as efficiently.




Not me thinking it at all. It's a fact you can verify in any text on the subject. If you look at the fuel pressure of modern cars, they are higher than they ever have been. The more the fuel is atomized, the more efficiently it burns. A good analogy is a carbed vs fuel injected engine. The carbed engine needed more fuel to account for the in efficiencies of atomization vs a fuel injected engine.

 

[dwcopple]

I should start a used air filter selling company...

 

[Smokescreen]

Maybe you can have mine when I am done with it...but not yet, its the original factory one (from 2008) with 134K kms (~84,000mi) on it and it still looks great and I still get an unchanged awesome fuel economy...maybe at the end of summer...maybe...

 

[sdowney717]

Notice comment number 5
http://www.3si.org/forum/f35/will-lowering-fuel-pressure-help-mpg-504064/

Quote:
I would look into buicks system. On the supercharged 3.8 liter they have a fuel pump relay that sends a lower voltage while under vacuum and high voltage when under boost.


Regardless of how much better the spray pattern with higher pressures, I got better mpg with lower pressure.

I know why they dont do this, because increasing the combustion temp with a leaner mix likely increases formation of NOx. But do I really care?

 

[Jim Allen]

Ah, using one opinion to bolster another. Looked like a pretty off-the wall exchange to me with no real fact being presented. Anyway, if you want to bone up on this, google the search terms "fuel pressure, atomization, fuel economy" and you'll turn up some interesting things. Have fun!

 

[Vikas]

Does your vehicle have a donut spare? If so install it and drive your vehicle for a whole tank respecting that donut.

Come back and be amazed at the mileage gains! (the mileage goes up because you drive lot more carefully with the donut and limit the highway speed to around 50mph) You would be surprised at how much gas that saves.