how does a fuel injector work?

[Anonymous]

well...i was thinkin the other day, and i was just wonderin how a fuel injecter works. I know that the thing plugs into a fuel rail, and has 2 wires...so I'm thinkin that it opens from current flow, is that right, if i were to stick a fuel line on the one end of the injector and have 12 volts or so going through the 2 wires (+/- i assume) then it would spray right....i will do some more thinking if this is how they work...could i get some info please? thanks. I may try something if this is how it works 8)

 

[addo]

That's basically correct. The electricals operate a solenoid not unlike the door locking sort, this opens a valve allowing fuel to pass and exit via the nozzle. Pressure is much higher than a carby fuel supply.

 

[Anonymous]

Pressure is much higher than a carby fuel supply.

hmmm...so would the fuel pretty much just dribble out or not come out at all then? Heres my idea...pretty simple. I wanted to have 1 or 2 injectors with the fuel supply teed off of the carbs fuel line, then mount them above the hole of the carb probably in the air filter or something like that...for the electrical signal i wanted to rig something up so that when i go WOT the current will close and the extra fuel will spray from the injector(s) allowing me to pretty much have 2 stages of fuel output on a 1 bbl carb...thus allowing me to better utilize my bored out carb for both fuel eficiency and power.....it would be cheap to do (junkyard parts and wire) and would be pretty fun to work on, i plan on going 2 bbl anyways later on but this would be great if it worked for now. thanks for your quick reply too.

 

[xctasy]

The idea is great, Dave, but there are a few issuues to contend with.


First. The injectors need enough space clear the cold start choke, and they have to be run off a Ford truck throttle position sensor. There needs to be an electronic structure which locks out the injectors on start up unless you want it to flood the beast. You could trigger the first injector via a Bosch map sensor in the intake, or just use the Manifold Absolute pressure sensor from an Alloy Head XF Falcon (I have one here if you need it). When the voltage indicates a sub 12"Hg pressure (little vaccum), it could jettison the first stage of fuel, when it goes below 6"Hg, it could then add the second injector to the party!


Second, the injectors need a standard line pressure to operate. Ford EFI pumps for port injection run 80 psi, and then have a return line to control fuel pressure at the injector. Since its hard to beat 7 psi with a stock Carter pump, each time you have a closed circuit cyle delievering 12volts to the injectors, you'll end up dropping the hydraulic head and float level. So the stock carby operation will be impaired. Remember, a 4.9 Six injector at 80% duty cylce can give enough fuel to give well over 40 hp, so two injectors is enough to create mayhem if they get locked on.

If you can get that operating without killing yourself, you'll be a the first EFI log headed 250 punter in the Americas! Rock on.

Oh, read the disclaimer below. We all believe in you and want you to suceed, but if the device fails, the Candian Mounties will be wanting my head on a spike for 'aiding and abetting' :roll: :x

 

[Anonymous]

Check out what this guy did. www.toohighpsi.com Look under the part that explains how to bulid your own turbo set up. There he explains how he added the extra fuel via a sigle injector mounted above the carb. Some TBI systems use as little as 15 to 20 lbs of pressure to operate.

Think of an injector as a speaker. The higher you turn the volume up the bigger and longer the pulse becomes. If you just want to skip the carb all together then you need to check out Mega Squirt. They offer a home bulit CPU and all the instruction to get you started. You would just need to gather all of the sencors and tune it using the down loaded program. I haven't personal done one yet but it sure is tempting. Hope this helps some, later.

 

[Lazy JW]

The injector is really just a tiny faucet that turns on and off electrically. The amount of fuel delivered is determined by how long it is turned on (duty cycle). In operation, the injectors cycle on and off real fast, during idle the are 'on' a small percentage of time and at WOT they are 'on' most of the time. This is all controlled by the computer which reads various sensors and adjusts duty cycle accordingly. Increasing pressure will give more flow, less pressure will reduce flow. The injectors are designed to work at certain pressures so it isn't adviseable to get carried away with that idea, better to go with a bigger injector if more fuel is truly needed.
Joe

 

[Anonymous]

Xtaxi: the idea was that the current would be N/A while idleing and cruising, the current would only be connected when u went WOT...i understand that part, i was thinking something very simple, just have a constant ground and for the AC i could have a setup so there is a wire on the kickdown rod (the part that touches the carb for WOT) and on the carb itself (the part that touches the kickdown for WOT) that way when your not in WOT the current is not complete and the injector would not be open, and when u go WOT the current would be complete, opening the injector. How does the MAP sensor work? would it be fairly simple to hook up for this? I'm guessing that the stock 250 mechanical fuel pump gives only about 4-5 PSI? what i get from what u said though is if the injector is open that i may not get enough fuel to the carb to fill the bowl. The pump works on a constant flow of pressure right? so if u were to block the one end of the fuel line it would still keep trying to give fuel and then your line would burst right? Or will it only produce that amount of fuel pressure and if there is a blockage will it not matter?

PS...and dont worry about the mounties...i think the worst thing you'll get is a nasty letter, lol.

I think i will do a test run of the injector with the 4 psi or so of fuel and see what its like, if it squirts up a decent amount of fuel then i will see if it supplies enough fuel to the carb bowl as well as the injector, i may just have to raise the float up a bit more than it is to compensate, but we'll see...it'll be this weekends little project i think. right now i am still trying to get my bored out carb working better (i just stuck in the larger jet again so it will run rich, sincce that seems the best performance al the way round...although the smaller jet seemed better at the low end..which is why i want to attempt this little project.) wish my engine luck :roll: and thanks lot for your info guys

 

[Anonymous]

Just wondering... could the jets be mounted alond the log. Then the Carb could act as normal, and using the above stated principle, have the jet only open at WOT. This "seems" simpler, but air/fuel mixture may be a problem? But I think that would be a problem regardless of the jets position. What do yall think?
Paul

 

[Anonymous]

actually i was thinking about that as well, and just use a smaller jet in the carb for even better gas mileage...but i dont know exactly what an injector looks like, but if it has a metal threaded end then that would probably be a better way to do it for sure....what about rinning a higher flowing fuel pump...7-9 PSI and having it tee off, but use a regulater to keep the fuel going to the carb at about 4-5?