Supra Forums banner
1 - 20 of 28 Posts

· Registered
Joined
·
737 Posts
Discussion Starter · #1 ·
OK so my friend and I are having a conversation about my injectors, He says I should put my 550cc precision injectors in, without any other fuel mods. While my head is off the block (BHG), I said no because it might do some damage. Well I'm a little confused because he says it wont' do anything, which I think I understand but I want a better understanding. Since injectors are controlled by the ECU that means they will only flow the 440cc of fuel when my 550cc injectors right??? I'm looking for some clarity here, and I'd like a better understanding of some things.

(Cliff Notes)
1. Convo with friend
2. Friend says put 550cc in without any other fuel mod.
3. Since injectors are controlled by the ECU that means they will only flow the 440cc of fuel when my 550cc injectors are put in right???
 

· Registered
Joined
·
348 Posts
NO your friend is wrong.

The amount of fuel is controlled by the injector pulse, fuel pressure, and flow rate which are all independent of each other. The ECU only contols the injector pulse, it doesnt know/contorl the injector size (flow rate)
 

· Registered
Joined
·
1,062 Posts
DeGrE u make me laff..... :rofl:
 

· Registered
Joined
·
737 Posts
Discussion Starter · #6 ·
my advice is take advice from a friend that actually knows something about cars.
\thread

He knows quite a bit about cars, but I guess he's not well acquainted with Fuel systems.
 

· Registered
Joined
·
737 Posts
Discussion Starter · #7 ·
Special K helped me out, is there anybody else that could chime in also, I would like to understand more.

Thanks
 

· Your ignorance...
Joined
·
985 Posts
In a nutshell:

The amount of gas going into your cylinder is determined by the following:
*size of injector (440cc, 550cc, etc)
*The pressure the fuel enters the injector at
*How long the injector is "on" (pulse width)


At a set PSI (say 40psi), there are two ways to make more fuel enter the cylinder:

1) Make the injector physically larger (go from 440cc to 550cc)
2) Make the injector stay open longer (ECU control)

The "cc" rating is only the maximum, meaning a 440cc injector will flow that 440cc's AT THE MAX, not that is is usually running at the max so you always have LESS than that amount, controlled by the ecu by 'pulsing' it on and off.

Now, the ECU has no way to know how big the injector is, so it uses the values programmed into it (440cc in our case). If you put a larger injector in there, it still thinks it is a 440cc and leaves it open just as long, HOWEVER you now have 25% more fuel coming out of the 25% larger injector, hence running RICH.

This is the theory behind the Lex AFM mod, you get extra unaccounted-for fuel to go with the extra unaccounted-for air from the AFM.



There is of course a lot more to fuel injection, but this is the basics of how it works, HTH!!
 

· Registered
Joined
·
70 Posts
In a nutshell:

The amount of gas going into your cylinder is determined by the following:
*size of injector (440cc, 550cc, etc)
*The pressure the fuel enters the injector at
*How long the injector is "on" (pulse width)


At a set PSI (say 40psi), there are two ways to make more fuel enter the cylinder:

1) Make the injector physically larger (go from 440cc to 550cc)
2) Make the injector stay open longer (ECU control)

The "cc" rating is only the maximum, meaning a 440cc injector will flow that 440cc's AT THE MAX, not that is is usually running at the max so you always have LESS than that amount, controlled by the ecu by 'pulsing' it on and off.

Now, the ECU has no way to know how big the injector is, so it uses the values programmed into it (440cc in our case). If you put a larger injector in there, it still thinks it is a 440cc and leaves it open just as long, HOWEVER you now have 25% more fuel coming out of the 25% larger injector, hence running RICH.

Exactly. Now you know why stock ECU have problems controlling 720cc and up. It dosnt know they are large injectors.
 

· Madd Tyte JDM yo ®
Joined
·
7,532 Posts
He knows quite a bit about cars, but I guess he's not well acquainted with Fuel systems.
well, he doesnt know fuel system, and that 33% of making an engine run. i assume hes only got a firm grasp on the other 66% (air and spark).. and a 66% is still an "F".

the ecu just controls how long the injector stays open.

one injector flows half a liter every minute
the other flows a WHOLE liter every minute.

the time they stay open is the same, which is what the ECU does. the injector is basically a bigger hole for fuel to come out of. to make the bigger hole flow less fuel, you make the ecu open the hole for a SHORTEr period of time.

To make the WHOLE-liter injector flow like the HALF-liter injector, cut its time in half; WHOLE Liter @ 30 seconds = Half Liter @ 60- seconds.
 

· Overlooked
Joined
·
4,693 Posts
Mk2racer pretty much hit it on the head. Three main variables; pulse width, rail pressure, size. There's others like dwell time etc but that's with tuning. If you have a FPR you can turn down the rail pressure if you decide to run the 550cc but I don't really recommend that lol. It's not really that hard to get to the fuel rail to swap them out later, we all know that.
 

· Registered
Joined
·
185 Posts
I'd have to somewhat disagree with the above posts. The stock ecu is able to adjust injector pulse by a fair amount in order to account for outside variables such as air temp, air density (or flow), temp, ect.. it does this with both the air flow meter to measure the air going in, and the O2 sensor to measure the the air to fuel ratio after combustion. If the ecu sees a rich mixture it will cut fuel back via injector pulse until it gets within it's preprogrammed parameters. As long as it is within the ecus adjustment range. Your 550's would probably by beyond the stock ecu's capabilities (hence "somewhat disagree") but if your friend had said "throw in some 490's" he would be mostly correct, it would compensate for it but it would be unlikely that you would notice any difference at all as far as power. I would wait until you have some form of tuning aid.
 

· Madd Tyte JDM yo ®
Joined
·
7,532 Posts
Yes except that properly running 7ms and 1js run near 10:1 under full boostafter 4300rpm and 5300rpm for the 1j, iirc. 100% stock fuel system too.

So he's/jamis is rght that 550s on a stock car will overfuel REALLY bad under any and all conditions. You'll need to pull out almost 12% fuel across the board just to start. That's just to keep the ecu within it's abilities of adjusting/trimmin the fuel. Under boost, it'd still be 10:1 and need to be scaled back too. So MORE THAN 12% after 4500 to get near 11.3-11.5 afr. As a side effect, it will put fuel cut farther away and allows you to run more boost now.
 

· Registered
Joined
·
2,895 Posts
I'd have to somewhat disagree with the above posts. The stock ecu is able to adjust injector pulse by a fair amount in order to account for outside variables such as air temp, air density (or flow), temp, ect.. it does this with both the air flow meter to measure the air going in, and the O2 sensor to measure the the air to fuel ratio after combustion. If the ecu sees a rich mixture it will cut fuel back via injector pulse until it gets within it's preprogrammed parameters. As long as it is within the ecus adjustment range. Your 550's would probably by beyond the stock ecu's capabilities (hence "somewhat disagree") but if your friend had said "throw in some 490's" he would be mostly correct, it would compensate for it but it would be unlikely that you would notice any difference at all as far as power. I would wait until you have some form of tuning aid.
sure, it does this at low throttle, where it receives O2 feedback. at high throttle, the ecu relies on predetermined mapping and ignores the O2 sensor as the narrowband loses accuracy away from stoichiometric afrs. throwing in 550 injectors will put you exteremly rich on an otherwise stock system. otherwise, there would be no point using the lexus AFM.
 

· Registered
Joined
·
877 Posts
Nice bump newbie. . . When are you starting the thread "my car keeps overheating what could it be? Has anyone else had this issue?". . . Please do me a favour and go to another forum. . .
 
1 - 20 of 28 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top