Why ASDF injection?

[iwontxlr8]

My first post it's long but enlightening. Thanks for your time.

I recently started attempting to maximize my MPG's. In doing so I inflated my tires, tune-up etc... I drive a 1993 Pontiac Sunbird 2.L MPFI and 5 speed manual transmission. This is a distributorless ignition system and I average between 33-36MPG and my comute is highway and street combined. My 1990 Sunbird 2.0L with distributer and 5 speed got 44 MPG! I am now obsessed with improving this 1993 and have added an HOH generator(uses electrolysis to produce and add gas to intake plenum) as well as cleaning out the car reducing the weight and removing the lower valance body work hanging below the front bumper in hopes of reducing the coefficient of drag. I even installed a limit switch on the accelerator to open up one of the fuel injector wires when I am not on the pedal. I figure this is a 25% saving when idleing downhills or while coasting to the next light. This helps save gas while keeping the vaccuum on the brakes and power steering pressure available, just in case. I still can't get the 1990 results. I am going to heat the fuel next.
To the point, in adding this switch I noticed the injector wiring harness only had 3 wires supplying 4 injectors. I immediately asked myself "How are they opening only 1 injector at a time with only 3 wires?" I purchased the 1993 Pontiac Sunbird factory service manual (ebay) and took a good read. On page 6E3-C2-1 lower right hand corner it states
"ALTERNATING SYNCHRONOUS DOUBLE FIRE(ASDF) FUEL INJECTION. For better fuel vaporization and improved emission control, fuel is injected at the intake valves when they are in the closed position. To do this, the fuel injectors are alternately pulsed in pairs so that injection for each cylinder begins Before Top Dead Center(BTDC). Injectors for cylinder 1 and 4 are electrically paired, as are the injectors for cylinders 2 and 3. Each pair of injectors is pulsed twice (double fire), once on the compression stroke and once on the exhaust stroke for each cylinder"
What the $#%& did I just read?
Anyone with experience or knowledge of the internal combustion engine explain this advantage. I thought injector is opened based on inputs from various sensors throttle position, speed and the ECM sends pulse width/duration signals to open the injector for longer/shorter periods to add or subtract fuel burned BTDC of the compression stroke. This is the only portion of Internal combustion engine(ICE) cycle to produce movement of the vehicle, isn't it? How does injecting fuel(the exact same volume used on the compression stroke) during the exhaust stroke help with improving performance, vaporization and especially emissions. How can injecting my gas into the exhaust pipe improve emissions? Vehicles with distributers fire the injector based on cam rotation and at degrees of cankshaft position BTDC on the compression stroke ONLY!!! To squirt gas into the exhaust chamber during the exhaust stroke merely ignites the fuel without producing any output to move the vehicle. Some may say "this helps to burn any fuel that didn't burn during the compression stroke" this is to improve emissions. PLeeeaase tell me how adding gas to unburnt gas improves emissions by burning unburnt gas. I am absolutely positive the same 1990 firing method could be installed on this vehicle with the crankshaft position sensor and count values. Maybe the manufacturers found a cost reduction from using less copper wire. Reprogramming the ECM prom possibly if not for the 3 wires. Thankully this 2.0L engine has the distributer hole cast into the cam carrier. I am going to get a distributer from the junkyard and run the injector wires through a modified rotor to the plug outputs and open the injectors on the compression stroke ONLY!!! I have to get significant gains this way. Currently only 50% of my fuel is used in propulsion. The other 50% only contributes to poor air quality and global warming as well as the size of the hole in mypocket.
Just introducing myself and making some of you aware this technology could be in your car. Sorry for the long read I hope you found it worth your time. Any thoughts

[KiwiBacon]

I'll take a stab in the dark.
Firing the injectors at the closed inlet valve during the exhaust stroke will be the hottest part of the cycle. That heat helps to vaporise the fuel.

Throw away that hydrogen system. Snake oil.

[taillight]

You would need to see the whole process to really understand. First the amount of fuel is adjusted by the sensors. It is called long term and short term fuel trim along with a preprogramed fuel injection. The sensors feed into the preprogram. The fuel needs to be at the intake valve as soon as it opens. The best way is to have it there before the valve opens so it is injected on both the compression and exhaust strokes behind the closed intake valve. That way on intake all of the fuel is ready to be drawn into the cylinder.

[GreyGoose006]

but doesnt it just sit there and form a pool instead of remaining in a gaseous mix that is so ideal for burning?

correct me if i am wrong, but this seems like a dumb idea on pontiacs part.

[UncleBob]

they gave dual bank injection a fancy name. Its not optimal though.

The most primitive system is a single bank injection, all injectors fired at the same time. Just about all modern cars, the injector is fired individually, and at lower RPM's is fired just before/during the intake stroke. The advantage of that being, better idle quality, and more importantly, better emissions at low RPM's

Once you get above 3000 RPM's, at the latest, it really doesn't matter at all, because the injector open time is longer than the intake stroke by a decent amount

and the bypassing an injector on decel is a total waste btw, the injectors shut off on decel

[UncleBob]

Originally Posted by GreyGoose006

but doesnt it just sit there and form a pool instead of remaining in a gaseous mix that is so ideal for burning?

correct me if i am wrong, but this seems like a dumb idea on pontiacs part.

keep in mind, we're talking about miliseconds. There's also a lot of turbulence in the intake. There will be some droplets that stick to the walls of the intake, but most of it will swirl around until the intake valve opens

[curtis73]

iwontxlr8, it doesn't really matter when the injector fires. Its still injecting it at the same place. You can't inject fuel into the exhaust chamber because there is no such thing. The intake valve is open during the intake stroke. The injector system you describe helps emissions and efficiency by injecting fuel on a closed valve that is approximately 600 degrees farenheit. It instantly evaporates a split second before the intake valve opens and gets drawn in. Since we know liquid fuel doesn't burn, they're thought is to help it vaporize more. If it works, it would help HC emissions and possibly a .0001 MPG increase.

I also don't wish to sound like I'm making light of your choice, but you do know there is no such thing as HOH, right? Its someone's way of renaming H2O that they've electrolyzed into H2 and O2. Its complete snake oil since it requires MORE energy to electrolyze the water than you get back by burning it. You're overtaxing your alternator to the tune of a few HP drag, so its taking more "foot" to maintain your speed which is a drag on MPG.

One of the other big things I suggest not doing is removing the front air dam. That will almost certainly hurt MPG. That air dam keeps air from getting under the car. When air gets under the car does two things; 1) creates drag on all the components under there, and 2) creates positive lift on the car. If you're creating lift, you're increasing drag. If that weren't true, planes could fly as high as they want without any more thrust, but its just something we have to deal with.

Some other reasons for MPG differences;
1) the 4- speed uses a higher (lower numerically) final drive ratio since top gear was 1:1 (no overdrive)
2) the older 2L engine made less power with smaller intake ports. Less power and less air means less fuel
3) they are slightly different in body style
4) chances are the older one had 195mm rubber on 14" or 15" wheels. The new one probably has 205 or 215mm rubber on heavier 16" wheels. If you want to pick up a few mpg, go with 185mm rubber. Trust me, its more than you need. I used to autocross a BMW with 195mm and it was just right. 205 or 215mm caused me to lose time. Wide tires look nice, but Americans seem to think they perform SO much better and they just don't.

Older EFI systems (and some still in use today) were batch fire or bank fire. There were only two injector pulses per every two revolutions on V8 engines. TPI engines fired all four on the left, then all four on the right. MPI with individual injector timing shows benefits in emissions, but has been proven over and over that it makes almost no difference at all in drivability, power, or torque. WHEN it fires them is of very little consequence.

[iwontxlr8]

I was trying to emphasize how adding gas to unburnt gas wont help burn it better and provide better emissions. I concur that it is not injected directly into the exhaust pipe. I should have said it better. I wanted to emphasize the method of opening the injector and allowing it to sit there and puddle could not help in emissions. Doesn't gas burn better if it is atomized better. The finer the mist the better the combustion or is all the fuel injector cleaning a waste of time in gaining more MPG

I am also curious as to dispensing in the intake during the exhaust stroke for the purpose of heating the gas. Won't the dispensed gas be pulled away from the intended cylinder from the vaccuum of adjacent cylinder/s on their intake stroke? If hotter gas makes for better combustion manufactures should heat it up first.

The body styles of the 1990 and 1993 Sunbird 2 door coupe are identical and the tire size also the same, in my case. The only difference between the two cars is the injection and ignition. According to the service parts identification label they both had a F68 final drive ratio 3:45. I made sure this remained the same. I really like the car and wanted to refurbish the 1993 and keep as many parts from the 1990 as possible.

My last tank of gas got 40.9MPG city. As far as hydrogen and snake oil, I am undecided to this point. I do credit the hydrogen generator with my awareness in consumption I was getting 28-30 around town and 33-36 highway before it all started. I employ some of the hypermiling techniques(if no one is behind me) I also disconnected the fuel injector at idle position and disconnected the O2 sensor along with removal of lower valance plastic piece.

I agree the injectors are shut off completely with rapid deceleration of the throttle, I wanted to continue this when I was sitting in traffic or traveling downhill. I have to be saving some gas with this because the engine is misfiring now. This can only be due to fuel starvation.

[iwontxlr8]

"You would need to see the whole process to really understand. First the amount of fuel is adjusted by the sensors. It is called long term and short term fuel trim along with a preprogramed fuel injection. The sensors feed into the preprogram. The fuel needs to be at the intake valve as soon as it opens. The best way is to have it there before the valve opens so it is injected on both the compression and exhaust strokes behind the closed intake valve. That way on intake all of the fuel is ready to be drawn into the cylinder."

I understand what you are saying here but with only 3 wires supplying 4 loads how does injector 1 and 4 differentiate between long and short and timing. The injectors are hard wired to the same piece of copper. So if injector 1 is on long trim during the intake stroke cyl 4 is also during it's exhaust stroke. This is because the signal shares the wire with 2 injectors. Injector #1 cannot be on long trim and #4 on short trim. This indicates to me something like injector 1 short term for exhaust stroke and long term for intake/combustion. At this time cyl 4 is just the opposite long term on exhaust and short for the intake. CYL 2 and 3 would act the same.

If we step back into the emissions discussion for a second and heating he fuel for better combustion would it not be better to individualize each injector with discrete signals so all of the get the optimal gas at the optimal time for combustion, emissions and fuel economy.

Sure we are only taking about msec in duration, but when you add up miliseconds the become seconds/minutes hours. If you hold an injector open at less than optimal time for combustion you suffer most in fuel economy. Manufacturers haven't made any significant gains in MPG in my 30 years of driving. These techniques are contributing to this.

[taillight]

Your right , for best fuel economy each injector should be fired seperately and some engines do. But for cost savings, some manufactures fire them in groups.

[curtis73]

Originally Posted by iwontxlr8

I wanted to emphasize the method of opening the injector and allowing it to sit there and puddle could not help in emissions. Doesn't gas burn better if it is atomized better. The finer the mist the better the combustion or is all the fuel injector cleaning a waste of time in gaining more MPG

Yes, it burns better, which is why they inject part of it against the valve. The valve is screaming hot, there is no puddling at all. Its like spraying water from a spray bottle on a 600-degree iron skillet. It instantly evaporates when it hits. The injector does a pretty good job of atomizing, but just spraying it past an open valve doesn't take advantage (in GM's eyes) of using the latent heat in the valve to evaporate fuel.

I am also curious as to dispensing in the intake during the exhaust stroke for the purpose of heating the gas. Won't the dispensed gas be pulled away from the intended cylinder from the vaccuum of adjacent cylinder/s on their intake stroke? If hotter gas makes for better combustion manufactures should heat it up first..

To a small extent, yes it will be drawn to another cylinder, but in batch-fire injection it doesn't matter. The injection system calculates how much fuel to inject and does it. Where it goes is a function of the geometry of the intake. The net result is the same; X amount of air and Y amount of fuel was ingested. If it made massive variations in fuel mix from cylinder to cylinder, GM would have either changed the EFI tune or the intake itself. But, like I said, its a VERY small effect. You could inject all of your fuel on the #1 valve during the compression stroke, meaning the other three cylinders suck their intake before the #1 does, and it would be fine. The column of air trapped in the #1 runner won't get sucked out.

In reference to manufacturers heating the fuel, to a certain degree they DO. You don't see insulation on the fuel rails, or the fuel lines. As with everything from manufacturers its a trade off. Hot fuel makes fewer emissions (except NOx) but it makes less power. Over the years they have become very experienced with controlling emissions and MPG with other methods, so using hot fuel isn't necessary. They can wring out a few more HP to compete with the Neon and still pass emissions using cooler fuel. But, its not COOL. Some time take some gas from the test port on the fuel rail after you've been in a store for a half hour. That fuel is HOT. Or squirt some fuel from some carb bowls with the accelerator pump in the same situation. They (particularly GM) designed their carbs to be on the verge of boiling the fuel; so much so that hot cars often times DO boil the fuel creating vapor lock

[UncleBob]

Originally Posted by iwontxlr8

I agree the injectors are shut off completely with rapid deceleration of the throttle, I wanted to continue this when I was sitting in traffic or traveling downhill. I have to be saving some gas with this because the engine is misfiring now. This can only be due to fuel starvation.

you're just increasing the injector time for the other 3 cylinders, as the engine tries to maintain an idle

Hell, disconnect 2 cylinders....assuming the IAC can keep up, it'll even run smoother

This is the kind of thing that a lab scope comes in handy. If you checked the injector time before and after, you could calculate if you're actually doing yourself any favors

[UncleBob]

Originally Posted by iwontxlr8

I understand what you are saying here but with only 3 wires supplying 4 loads how does injector 1 and 4 differentiate between long and short and [long] timing.

short term fuel trim and long term fuel trim two variables that the computer keeps track to calculate the final open injector time for any particular moment. Its how the computer learns and adapts to changing engine management changes.

The long term is the accumalation of the O2 signitures for that VE cell. IE, at idle, with X KPA, it has noticed over the long term that it likes -10% of the base injector time. So thats the first part of the equation

The short term is what the O2 is currently showing. This is added into the formula for the final number of the next injector firing. The O2 is moving up and down as it fluctuates between .2V and .8V. So lets say the O2 says the last firing was -5% (it was richer than it should be) The computer takes its long term and short term and adds them together. -15% is the new fuel trim, and using this, it will take -15% out of the next injector pulse

There is no individual calculation for different cylinders. They are all being fed the same data from the O2 sensor, so they are all using the exact same calculations. Doesn't matter if you have individual injector drivers or batch injector drivers......the number of pre-cat O2's are what determine the number of seperate fuel calculations. All 4 cylinders and many 6 and 8 cylinders use only 1 O2 sensor, so its "global" for all the injectors