MPG (miles per "USA"gallon) ,
My car sucks too much fuel (gas) (over uses, or wastes) , my fuel economy is horrible, etc.
What is a Gallon?, seems an easy question and is, inside confines of USA.
The USA EPA 1995 spec MPG , is 19 to 30 MPG]US], << see arrows! in linked photo?, with E0 fuel (gasoline pure) E10 a tad less, a 1/2 mpg?)
My 2 Dr.-5speed, does 28 MPG one E10 fuel. (open road !) 60MPH. (unloaded and flat ground)
The same car gets 34 Miles per Imperial gallon[UK]. 20% more due to the large gallon size. Even a tad more on E0 fuel
E0 is pure gasoline (octane) E10 is 10% Ethanal.
Our engines (EFI) are not tuned to get good Ethanol mileage.
The metric fuel economy is 8.4Liter /100km
Most of these cars with 15MPG[USA] are STUCK in limphome mode. (most)
An Example of REAL MPG DATA here are may owners, reporting , add yours. (these are mostly mixed, MPG, so are lower)
If engine issues are the cause of low MPG, it us usually due to bad Combustion. (too rich tops list)
Don't let MPG make you sad, like this: (funny Geo Metro jokes, a 50 MPG[US] car )
See Hitlers RANTS ON MPG FAILURE ! (the 3 speed joke, is the best...) "why make a 50 MPG car, then wreck it, with that 3speed ?"
BAD MPG is: (pure physics and errors)
Top reasons for poor MPG: (common or macro reasons)
Cockpit Errors or others.
In the city you are accelerating over and over and wasting forward momentum at each stop. (both acts, waste fuel)
On the open road the MPG will be best at 14.7:1 AFR, this is the point, that every molecule of fuel is burned, with oxygen. every drop.
This is how you get good MPG good on the open road and keep the AFR at STOICH, 14.7:1 and you will get 28mpg with E10. I do. (2dr .5sp)
To get better city mileage it takes careful driving, and not stopping. No fast right foot actions.
(mosly, impossible, and my point here)
If your tire/wheels spin freely (jack up car, and spin it by hand, must be an easy spin, no drad) then your engine is running super bad.
The engine can only do 2 things, make lots of power efficiently or blow heat and raw gas out the tail pipe.
The engine can burn all the fuel or waste it. (incomplete combustion will caused bad MPG) MISFIRE is the top reason, is thet EFI over fueling ?
Top Solutions: (Micro) (no order , order is dictated by FATE)
What is, "Close Loop"? , is when the Oxygen sensor is holding the Engine at best MPG. Open loop is when the oxygen sensor is shut down , for passing or wideopen throttle.
The purpose (besides SMOG) for closed loop is to BURN every drop of fuel. Not waste it. Read this book from Mr. Banish, for the full story. (best of best)[mech, engineer]
Close loop failures, are caused by many things. (but the EFI is out of control , if the hot engine fails to enter Closed loop at idle or light steady cruise)
What does MPG look like?, well , this plot was done on my 96 with a full OBD2 scan tool and Laptop. See the instantaneous MPG? See the complexity?
The above car is a 5speed 2door 4wd and has a 95hp 16v motor that produces max. torque at 4000 RPM. I get 29MPG.
Other motors have different sweet spots, due to different motors and transmissions ,etc.
Best practice, is to buy or make an MPG gauge (#11) and discover your cars MPG sweet spot in each gear, and learn to drive all over again, For Sure.
A cheaper way is to make a closed loop LED, for the dash, my MPG gauges has one. Drive and keep this simple light glowing and MPG will happen.
Commentary: It's called a heat engine.
In the Otto Cycle engine, where does all my fuel get lost (ICE= internal combustion engine) . See it here, it is lost as HEAT !
Automatic transmissions: A/T
These old school , A/T gear boxes are a big waste of fuel , newer cars have 9 speeds. or CVS or dual shifted auto , M/T boxes (Porsche)
They (A/T) slips every time you accelerate and turns fuel to pure wasted heat.
The A/T does quite will, out on the open road, with the TCC locked up; sure does. but wastes fuel ever time you down shift or take off from low speeds.
The new A/T has 9 speeds and a 2 speed tranny oil pump, that does not waste huge energy (@ a2-kw) at every stop signal, at a dead stop, while in "Drive", selected.
Pure Physics!: ( Saving money is the deal, but saving fuel and saving money are NOT the same thing. but Cost of ownership, is the topic)
COASTING, etc: IMO:
Only fools, hypermil , that is, tail gate other cars,etc. IMO ! or drafting big trucks. (gas is cheap , death ,$$$$ and inconvenient big time)
Coasting in neutral gear is dangerous and illegal in most States, for good cause.
Coasting in gear, is the way to go, down any hill, in top gear, if you can keep legal speeds, if not down shift and use the engine braking to slow car to safe legal speeds. (saves fuel)
Coasting in gear , and lets the EFI use cut fuel mode. zero fuel flows, when coasting in gear , down hill. I'm a life time coaster.
The first automatic transmissions using hydraulic fluid were developed by General Motors during the 1930s and introduced in the 1940 Oldsmobile as the "Hydra-Matic" transmission.
This helps to understand why old A/T waste fuel.
Books to read, just one, the best by Jeff Hartman. ISBN-13: 978-0760315828
Better or just as good is the Mr Banish book.
Read this book from Mr. Banish, for the full story. (best of best)[mech, engineer]
Top reasons, for bad MPG not the 50 listed under misfire and flooding for gross fuel waste are: (just engine, not cockpit reasons, not bad fuel)
See real MPG live and instant MPG, below, the true MPG is the average of all those spikes. Test car: 1996 2dr, 5speed, 4wd in 2wd mode. a 2000 lb car.
The below is driving on country roads, below 45 MPH, and those spikes are cut fuel mode, coasting.
To find you cars maximum open road MPG, just log this data and find what speed on flat ground gives you the highest MPG.
My newer Jeep JK 2008, I have a factory MPG gauge. and can see instant and average mpg driving.
What happens , in real time , is every time you Accelerate or drive too fast, the average mpg drops.
The below data was pulled using a cheap ELM327 scan tool, then plotted.
The less air you engine sucks with the MAF, the more MPG you get, and the longer the coasting and less braking....too. The script is from "Palmer Performance Engineering"
My next graph, is trying to get 40mpg. (just at 1 speed, and gear) the average will always be less.
The spikes are shift points, and cut fuel mode.
This is Not flat ground it's rolling hills an stops.
Lets say , I'm getting 15 MPG (USA gallons) 15 Miles per gallon, that is 150 miles on 10 gallons of fuel MPG = Miles divided by gallons.
Not only that, the fuel was not stolen, and my GPS shows, my mileage really was 150 miles driven.
I do not have dragging brakes, I check that carefully, by hand (spun tires by hand, I did.)
I suspect my engine is running badly. (I did the full 60,000 mile tuneup per the operator guide.)
My check engine light (CEL) is on, telling me , it has problems. DTC P0171 In all cases, I . find the cause of this first. This DTC, means the fuel trim is way off the pass/fail rails.
I next connect my scan tool and see if the hot engine holds closed loop status at idle and that idle is near 800 RPM (± 50 RPM) HOT ! If not?, I find out why , now.
I next drive the car while my friend scans the ECU/PCM, and to see if on flat ground, at a steady easy cruise, say 45 MPH, the PCM holds closed loop status, if not? ,fix that next.
The early cars are very hard to check for closed loop status, due to Suzuki (inanely) not publishing their stinky OBD1 protocol.
In all cases,I check my ECU/PCM long term fuel trim is not over 10% or out of control.
OBD1, 1989 to 1995 (USA)
The closed loop can be seen with a scope, connected to the oxygen sensor CELL pins. (not the heater pins)
If the sensor swings fast, say 3 to 6 times a second, it is , in closed loop.
One other way is to watch spark (1991 to 1995) advance as you race the engine fast in neutral or park, and see timing move way out to near 40 Degree's before top dead center BTDC. If not?, it is in limphome mode.
The OBD1 DTC code 13 , is very very poor monitor and shows 13s only if the fueling is HORRID. It is not reliable at all, this monitor 13. I pretend it don't even exist.
Trouble shooting all non OBD2 cars, is a pain, all tests must be done by hand and with a DMM and scope. (all sensors. and check spark timing very carefully)
Finding a scan tool is not easy. ( there are some crude hacking tools about)
On any 1989/90 Sidekick, with the crude , manual distributor, make sure the thing, advances spark properly first, then check ECU LAST. Both the fly weight spark and vacuum ! BOTH!
The engine will NOT burn all the fuel , unless spark is advancing proper.
rev 15: 5-11-2014 ( started in 2007) added graphics.
The cheapest gas you will ever find, is the gas you didn't burn. (move closer to work?)