325E stock fuel injector flow rates?

[ldzpstnr]

Anyone know the flow rates for the stock injectors on an ETA 2.7 engine? They are not he same injectors as the 325i. The "I" cars use an injector that has a higher ohm resistance reading then the "E" car. I was wanting to get bigger injectors until I ran into this low resistance injector problem.

I have been wondering if I could in fact use the "I" injectors if I was to put an in-line resister for each injector, and get the oh resistance down to the 2-3 ohm requirement, instead of the "I" 13 to 17 ohms or whatever it was.

Any info on this? Thanks.

 

[Rukus]

you can't get resistance DOWN from 13-17 ohms to 2-3 ohms by ADDING resistance (resistors)

You can only INCREASE resistance by adding a resistor (resistance)
17ohms resistance + 1 ohm resistor (resistance) = 18 ohms resistance.

also Remember ohms Law:


For voltage [V = I * R] V (volts) = I (current) * R (resistance) OR 12 volts = 2 amperes * 6 ohms

For current [I = V / R] I (current) = V (volts) / R (resistance) OR 2 amperes = 12 volts / 6 ohms

For resistance [R = V / I] R (resistance) = V (volts) / I (current) OR 6 ohms = 12 volts / 2 amperes

 

[ldzpstnr]

Thanks for the info about OHMS Rukus. I do not have very much knowledge of OHMs and such so your post really helps.

Sounds like it just might be best to replace the motronic system with a fuel system from a place like www.sdsefi.com or something. I am going to crank up the power in my E30 this summer I hope. Going to need more fuel.

 

[Rukus]

simple knowledge about physics and elctricity are VERY helpful to owning a car and doing performance mods on your car.

 

[bichmgnt]

Resistance could be lowered by putting the resistor in parallel with the injector. To go from 15 ohms to ~3 ohms would require a 0.5 ohm resistor in parallel with the injector. At 12 volts that would be 24 amps being used by the resistor. I'd expect that would get pretty hot.

You'd have to talk to someone more knowledgeable about injectors than me to see if it would really work.

Steve

 

[ldzpstnr]

Sounds kinda risky to me. I dont want to risk a fire Sounds best to just replace the motronic system.

What about the injector flow rates? Anyone got any idea about them?

 

[Rukus]

how do you put a resistor in parallel with one injector? (there is no way)

the injector is a single item on working on its own circuit. You can't wire it in parallel. you cna only run a resistor in series with the 1 (one) injector. and like i said in my last post, adding a resistor increases ohmage.

Its not like wiring two subwoofesr in parallel. Besides even if you could wire the injector that way, it doesn't change the ohms of the injector, only the load (less ohms, less resistance, more current running through ECU) on the power supply TO the injector, most likely resulting in frying your ECU. (which is your power supply to the injector. So lets say you do decide to try to wire your injectors in parallel

say you have two 10 ohm injectors (the only way to wire an injector in parallel, is to take 2 injectors and put them in parallel, unless of course you run an injector in parallel with a resistor, like bichmgnet said, so replace where i make reference to the 2nd injecftor, as a resistor instead)). (i am so not rewriting all of this)
a 10 ohm injector is a 10 ohm injector.

so therefore, to understand waht i mean, take this formula: it explains what you get when you wire two 10 ohm injectors in parallel

1 / R = 1 / R1 + 1 / R2 + 1 / R3 +...
so adding two 10 ohm injectors in parallel:
1 / R = 1/10 + 1/10 = 1/2 or 5 ohms. (half the resistance of one injector running in series! (bad))

So NOW the load on your ECU is 5 ohms instead of 10 ohms , and your injector's rated ohms have not changed, your 10 ohm injector is still a 10 ohm injector.
because the ECU doesn't know or doesn't care that its a 10 ohm injector, that 10 ohm injector is STILL getting the rated V= IR current that it was deisgned to get.

V=IR

V = 12
I=?
R=10

solve for I
12 = I 10

I = 1.2

now to understand hpow the load on your ECU applies to 2 injector running in parallel, i am going to take the resulting addition of the 2 injectors in parellel, which we found was a 5 ohm load on the ECU

V=IR

V=12
I=?
R=5

12=I 5

I=2.4

Now the current running through your ECU is 2.4
split that in half??? each injecotr still gets an original equal 1.2 amperes of current just as if you never ran your injectors in parallel at all Your ECU is working TWICE as hard to get the same results as wiring your injectors normally and your ECU will most likely fry.

your best bet?

don't bandaid fix your car with resistors. spend the extra amount of money it takes to get the proper injector or engine managment system for your car.


Feel free to ask my any questions if you find this confusing.

 

[Rukus]

new stuff. edited.

 

[ldzpstnr]

Wow Rukus. Nice post. Yea I wont be trying the resistor idea, new ECU sounds the easiest way to go. A lot of that is greek to me but I understand the basics. Sounds like a bad idea.


Later

 

[Rukus]

just to be clear... a 10 ohm injector is a 10 ohm injector no matter HOW you rewire it. you can't physically change the characteristics of an injector by wiring it in, parallel. the ONLY thing that changes is the load on your power supply or (ECU). (which does you no good anyways)

 

[bichmgnt]

how do you put a resistor in parallel with one injector? (there is no way)

You can't put a resistor in parallel with the injector? There is no way? I beg to differ. All you have to do is put it across the two wires that go to the injector. It's exactly the same as wiring two subwoofers in parallel. And wiring two injectors in parallel would make both injectors fire at the same time which wouldn't do any good so I'm not sure why you used that example.

What if there's only one wire that goes to the injector? That means the injector is using the engine as a ground and all you have to do is put a resistor from the injector wire to ground.

Both ways the resistor is wired in parallel with the injector. Both ways the resistor is only affecting the injector it is connected to. Both ways the ECU sees the resistance it is expecting. And both ways the injector is still seeing 12 volts and is using its normal amount of current. The only thing that is different is that the resistor is now drawing the current that the original 3 ohm injector would have drawn minus what the new injector is drawing.

The whole point of putting resistors in the circuit is to keep the load on the ECU the same as if it had the right injectors in it. The original 3 ohm injector draws a lot more current from the ECU than the 15 ohm injector.

1/R = 1/R1 + 1/R2

1/3 = 1/15 + 1/X

Multiply both sides by 45

15 = 3 + 45/X

12 = 45/X

X = 3.75 ohms ( A correction from my earlier post)

If a 3.75 ohm resistor wired in parallel with the new 15 ohm injector, the resistance that the ECU sees is 3 ohms and the voltage the injector sees is 12 volts. Both are getting what they expect. The resistor probably doesn't get that hot either because the duty cycle on it is probably only 20% or less at full throttle.

I = E/R

I = 12v/3.75 ohms = 3.2 Amps

E x I = Power

12v x 3.2A = 38.4 watts

At a 20% duty cycle

38.4 x 0.2 = 7.68 watts.

8 watts will feel barely warm let alone start a fire.

The new injector, following the same equations, draws 1.92 watts.

The old injector draws 12/3 x 12 x 0.2 = 9.6 watts = 7.68 +1.92.

With the old injector or the new one with the resistor in parallel, the ECU is putting out 4 amps while the injector is on.

If you wanted to do it the other way where you wanted to use the 3 ohm injector in a system that needed to to see 15 ohms, putting a 12 ohm resistor in series with the injector wouldn't work. The ECU would see the right resistance but the resistor is now dropping 9.6 volts and the injector is only seeing 2.4 volts.

I never said it was a good idea. As a matter of fact I said to check with someone else. But it was flat out wrong to say that you can't put a resistor in parallel with an injector.

Class is over. There'll be a pop quiz tomorrow based on the homework. Permission slips for the field trip to the chocolate factory have to turned in no later than Tuesday or you'll be staying behind and licking envelopes for Principal Skinner.

Steve

 

[Rukus]

i really don't understand where you are going with this, and if you evne read my post.

he wants to put higher ohms injectors on an ECU that calls for lower ohm injectors.

A 10 ohm injector is a 10 ohm injector, no matter how you wire it!! its going to draw the same amount of current. and its going to do the same thing it was designed to do!!!!! its going to behave normally. wire in parallel or not.

sorry if my example wasn't exactly along the lines of what we were talking about, it was merely an example of why you DON"T WANT TO wire in a resistor in parallel. you can wire your injectors any damn way you want. i never mean it was impossible.

still your post is very unclear to me, maybe you want to draw me up some diagrams?

<quote> All you have to do is put it across the two wires that go to the injector </quote>

and isn't that EXACTLY what i wrote about? you just explained waht i said all over again. come on buddy do the math before you try to act all big. a 10 ohm injector is a 10 ohm injector, no matter how you wire it, and AGAIN... V=IR will prove that. all you are doing with that resistor is changing the load on the ECU. not the physcial quality's of that injector.

 

[Rukus]

its not that you should try to trick the ECU to THINK its a 3 ohm resistor instead of a 10 ohm resistor, thats not a factor that determines the way the ECU operates (fuel rate flow, response.. etc), thats determined by your ECU map and various sensros connected to the ECU
its trying to have an injector that can properly operate with the signal or current that the ECU puts out
if the ecu only puts out 2 amperes of current which is sufficent for a 3 ohm injector, on a 10 ohm injector, current is going to be significantly reduced. Which would obviously affect injecotr reponse and rate of fuel flow.
no matter WHAT you do.

sure, do the resitor trick, yes your ECU puts out more current, buts its distributed evenly across the resitor and the injector. the injector still draws the same amount of current and the resistor draws the difference.

 

[bichmgnt]

You're right. He wants to put a bigger injector with a higher resistance in place of the original injector with a lower resistance. His idea was to add a resistor to the circuit of new injector so the ECU doesn't see the difference. You said he couldn't lower the resistance of the circuit, only raise it by putting a resistor in series with the resistor. I said he could put a resistor in parallel with the injector to lower the resistance. You said there is no way a resistor could be put in parallel with the injector. But all you have to do is put the resistor across the two wires that go to the injector and here's how.

Two wires go to each injector. One of the wires going to the injector gets pulsed with 12 volts when the ECU wants the injector to spray fuel. That is the hot wire. The other wire is a ground. Both go to the ECU which provides the current. The injector is the load on the circuit. If you pull the plug off the injector it's an open circuit. Infinite resistance and no current. Depending on the design of the ECU the voltage could go up as well but it is probably switching battery voltage so it won't go up much.

If you connect a resistor between the hot wire and the ground wire somewhere behind the plug, the ECU sees the simple resistance of that resistor. Using my calculations from the previous post, it would see a simple series load of 3.75 ohms. If you then put the plug onto the new injector, the resistor is then wired in parallel with the injector and the ECU sees the resistance of the injector and resistor wired in parallel. The injector still gets the full 12 volt pulse and yes since it's now a 15 ohm injector it only draws 0.8 amps while being pulsed. The resistor draws 3.2 amps while being pulsed and the ECU can't tell the difference between that and the 3 ohm injector because the injector and the resistor together are drawing the 4 amps the ECU is expecting to see. The injector doesn't care that there is a resistor across the wires that go to it because the ECU puts out enough current to supply both.

So the ECU sees the same load and the injector is getting 12 volts. The real question is what's happening. The injector, although it has a different resistance than the original, might still put out a similar amount of fuel for a pulse of the same duration. Or it doesn't. It might put out more. After all, it's a bigger injector. But it might put out less. It depends on how the injector is designed.

Bigger means it has the capability to put out more fuel over a period of time than a smaller injector. But it doesn't necessarily mean that it puts out more fuel for a pulse of the same duration. Probably but not necessarily. It depends on how the injector is designed.

The ECU, after a while, might be able to adjust for it by putting out shorter or longer pulses after seeing how much oxygen is in the exhaust. The problem is there could be a limit as to how short or long a pulse the ECU can put out. It depends on how the ECU is designed.

There is another variable - fuel pressure. By lowering (or raising) the fuel pressure the bigger injector might now be putting out the same amount of fuel for the same duration pulse.

So at this point the ECU is seeing the right amount of current, the injector is putting out the same amount of fuel and everything should be happy. But since I am not an expert on fuel injection systems I might be missing something. That is why I said to consult someone much more knowledgeable about it than me.

Steve

 

[bichmgnt]

One last thing. All the injector cares about is seeing 12 volts. If the ECU can provide it 12 volts at whatever resistance the injector is happy. The fuel doesn't care how much resistance the injector has or how much current the injector is drawing whereas the ECU might. The only thing that matters is that the injector sees 12 volts and it opens up and sprays fuel. As a matter of fact, an injector with higher resistance probably reacts faster and cleaner with less current going through it than the higher current injector. An injector is essentially a fuel relay. Power gets applied to the relay, it opens, and out comes fuel. It takes time to build up current when going through a coil because of the inductance of the coil. Less current means less time it takes to build up to the max for a coil of the same induction. But it does not necessarily follow that less current means lowered injector response or rate of fuel flow.

There is one thing that I didn't take into consideration when writing the post above and that is the fact that a resistor across a coil creates a filter circuit. Even though this is DC, it is being turned on and off at varying rates which makes the voltage look like a square wave. This might cause a problem at some RPMs based on how much induction the coil has but I would have to do some research to put some reasonable numbers together. It might make no difference at all and it might make your engine sputter at a certain RPM. Considering these engines aren't run at more than 7000 RPM that is only a square wave at less than 60 Hz. It's unlikely the filter would be lower than that. Still, that is why you need to talk to someone more knowledgeable. Or just put in the different ECU with matched injectors and be done with it. Please.

Peace. Out.

Steve

 

[chucko]

Do you guys agree or disagree?????????????? I'm confused..............and I majored in EE[???1]

 

[Rukus]

I am seriously done arguing with you. Not that i feel i ahve lost, but i feel you have lost total judgment on the subject.

the voltage has nothing to do with how the circuit works. its only how many volts that the battery puts out to all electronics in the car. Its basically only a variable that determines current when put into the formula V=IR, with a resistance variable. Current is the most important factor in this argument.

 

[bichmgnt]

I don't know. It seems to me that Rukus is saying the 15 ohm injector won''t work right with an ECU that is designed to work with a 3 ohm injector because the injector is drawing less current. I'm saying the injector would work just fine because it is getting 12 volts and is able to draw its normal current which is all it cares about. I saying that adding the resistor makes the ECU think the injector still has 3 ohms resistance. It might not even be necessary. The ECU might not care as long as the injector is working and putting out the right amount of fuel.

The stock 325e injector has a flow rate of 133 cc/minute and the stock 325i injector has a flow rate of 149 cc/min. That answers ldzpstnr's original question. The ECU should be able to handle the difference in flow rate by shortening the pulse. And if not the fuel pressure could be lowered to accomodate the bigger injector.

And because he asked for a diagram:

 

[Rukus]

my last comment is.....

A smart person wouldn't suggest a bandaid fix.

I don't suggest anyone bandaid fixing your car with resistors. Spend the extra money and do it right.

 

[bichmgnt]

my last comment is.....

A smart person wouldn't suggest a bandaid fix.

I don't suggest anyone bandaid fixing your car with resistors. Spend the extra money and do it right.

1. No one ever suggested that using the resistors was the right thing to do. As a matter of fact, I repeatedly suggested to talk to a professional before doing it. I only got into this to correct your erroneous statement that a resistor could not be put in parallel with the injector.

2. The more I look at it the more I'm beginning to think that the whole system would work just fine by putting the new injectors in and not doing anything else. Just because the injector draws less current doesn't mean it isn't working just as well as one that draws more current. It is still putting out the same amount of fuel. It just uses less current to do it. It's more efficient.

The only thing the ECU changes in response to the input from the sensors is the frequency of the pulses and the length of the pulses. Frequency in response to engine speed and length in response to the oxygen sensor. The sensors don't determine how much current goes to the injector, only V = IR does that. And since V and R are constant, I is always constant. The only difference here is that R is higher for the new injector which means I is lower. It's a different constant. The injector still works exactly as it is designed to.

There would be a problem if you tried to put the three ohm injector with the 15 ohm ECU. You would likely burn out the ECU because the injectors draw too much current. But the injectors would work just fine as long as the ECU held out.

ldzpstnr, I say if you have the injectors and want to try it out, give it a shot. Since the newer injectors are drawing one-fifth the current I doubt that that you can hurt anything. And I would be willing to bet that it works without any other modification. There's only a ~10% difference in the flow rates of the injectors and the ECU should be able to handle that without much of a hiccup.

I appreciate this discussion because I am going to be putting the 192 cc/minute injectors into my 325iC sometime in the near future and this has solidified some points for me. I think we're saying a lot of the same things but, Rukus, your insistance that the lower current is a problem is difficult for me to understand.

Steve