Fuel injector resistors

[Wakkolio]

I am curious to know how do you go and make the resistors for low impedance injectors to work for the ka24de?

Thanks

[klattr1]

there are wires coming off of the back of your ECU. You find out which wire is what and locate the injector #1,2,3, and 4 wires on the back of the ecu. You cut and splice the resistor inline of the wire for each injector wire. The resistor has 2 ends to it(Ballast) and you sauder each end to existing wire that was cut.Pretty easy job. The main thing is knowing what wire is what.I got the wiring stuff and diagrams off of 240sx.org faq's.

[Pornflakes]

I am curious to know how do you go and make the resistors for low impedance injectors to work for the ka24de?

Thanks

You place one 6.8 ohm, 10 watt resistor in series with each injector....like this:

[tony/ka24de]

can I control bigger injectors by using resistors? And then change the resistors until I get the amount of fuel I want?

[tony/ka24de]

what do they mean by low impedance injectors ?

[WAbernethy]

Some injectors are low impedance (2 or 3 Ohm) and some are higher (12 or 15). I know the sohc uses high impedance injectors. So when I put in my bigger injectors(low imp.) I also wired a 10 Ohm resistor in series with each of them. You cannot switch to bigger injectors and "tune" them using resistors. It would proly burn out the driver circuirty for the injectors if you try. You'll have to buy a SAFC or something similar to use bigger injectors.

[erich]

Thre are basically two types of injector drivers in cars. The Peak/hold and the saturated switch. The 240 uses the saturated switch type.

Here is the difference. The saturated switch type is like a switch in line with the injector. When it turns on the FULL BATTERY VOLTAGE goes across the injector. High impedence injectors are about 12 ohms, giving a little over 1 amp of current. If you use a low impedence injector which is usally 2-3 ohms you get 4-6 amps of current. Injectors are usually made to take 1 amp of current for extended durations. Running a low impedence injector with a saturated driver will burn it out, and probably burn out the driver as well.The peak/hold driver monitors the current through the injector. Usually they run 4 amp turn on current for at most a millisecond followed by a hold current of 1 amp for the duration of the injector on time. Peak/hold style injectors turn on faster which gives you better idle fuel delivery with big (>72lb/hr) injectors.So, if you put ~10 ohm resistors inline with the injector it will lower the current drawn by the injector to about 1 amp allowing you to use low impedence injectors with saturated drivers. You lose some high speed response but you have little choice.

[Pornflakes]

can I control bigger injectors by using resistors? And then change the resistors until I get the amount of fuel I want?

Correct. You cannot control injectors by using larger resistors. Injectors are not controlled by how much voltage is supplied to them, but rather by pulse width (how long they receive the voltage for, and how long they don't). Injectors are either "ON" or "OFF". At idle, for example, my injectors are on for 1.25 millisecond, and off for the rest of the time until it's their turn to inject again. At higher RPM, they are on for 3 ms and off for the rest of the time. The maximum they should be on is 85% of the time (to be safe and consistent). If they're on 100% of the time or close to that, they're running static (they no longer pulse, but are now open the whole time). When this happens, you need larger injectors for the task.

High impedance injectors are around 12 ohm, and are of "saturated circuit" type. The ECU supplies 12 volts to the injectors and the ECU turns this 12 volts on and off to establish a fuel injector pulse. Because of this 12 volts/12 ohm circuitry, the injectors will draw 1 amp (12volts divided by 12 ohms). So, this injector will open each time 1 amp of current (or slightly less) flows through it. High impedance injector usually take around 2 ms to open once they're activated.

Low resistance injectors are around 2 ohms, and are of "peak and hold" type because they use a peak and hold driver to activate them. These injectors need a peak current (about 4 amps) to quickly jolt them open, and then a hold current (about 1 amp) to keep them open for as long as they need to be. These injectors will also open at less than 4 amps (as long as it's more than 1 amp), but will not provide the same quick response as when it's opened with a current of around 4 amps. For this reason, they will still operate with "our stock" ECUs if connected with a resistor in series. Since this injector has a 2 ohm impedance and the resistor in series has a 6.8 ohm impedance, we have a total of 8.8 ohms. The stock ECU still provides 12 volts. 12 volts divided by 8.8 ohms equals about 1.4 amps. This is indeed enough to open the injector. Low impedance take around 1.2 to 1.5 ms to open once they're activated properly (4 amp/1 amp method).

I hope this gives some more insight.

[Pornflakes]

Oops...you beat my post by a few minutes erich

[erich]

Haa Haaa.

[tony/ka24de]

thanks guys.

[tony/ka24de]

does the mafs give the signal for the pulse width? And now that my car is boosted, will the mafs see the air being forced in and try to open my injectors more?

[rco8786]

does the mafs give the signal for the pulse width? And now that my car is boosted, will the mafs see the air being forced in and try to open my injectors more?

Indirectly, yes. Correct me if I'm wrong but the maf feeds info to ecu, which feeds info to injectors about how long to stay open. and it u have bigger injector and the ecu doesn't know about it you will be dumping fuel into ur motor.

[Pornflakes]

The ECU controls the injectors based on both MAF and RPM signal. If you upgrade to bigger injectors, you need to re-program the ECU to let it know that you now have larger injectors. A 500cc/min injector that opens for 1ms will squirt as much fuel as a 250cc/min injector that opens for 2ms. So if you originally had 250cc/min injectors in your engine and you upgraded to 500cc injectors, you now have to re-program the ECU to tell it to open the injectors for half the time it used to (at the same exact time as before, but just half the pulse) all throughout the MAF/RPM table.

Answering your boost question, whatever air that goes into the engine (boosted or not boosted) will have to go through the MAF first. Therefore, the MAF will always read all the air that's coming in, and let the ECU know. There is a limit to what amount of air the MAF can read though. The stock MAF, for example, will max out at about 250~300HP worth of air (enough air supply to produce 250~300HP). A Mustang Cobra MAF will do 500~550HP, for example.

[tony/ka24de]

I probably would not do this,but correct me if I'm wrong. If i were to put 370cc injectors on to my car. And then put a resistor on the mafs signal wire(would have to calculate the percentage)(370's are approx 37% bigger.) Install a resistor that would reduce signal by 37%, the car should still run like stock injectors did. ( Not sure, just trying to learn more) thanks for your replys

[Nathan]

Nope, it wont work...the computer will still tell the injectors to stay open for the same length of time and thats the problem, you'll just change the voltage going to the injector but not the pulse width which is what matters with different size injectors.

[s86d]

so would there be any way to change the pulse width w/o ecu tampering???

[Nathan]

I dunno...the discussion is getting a little past my technical knowledge, I hope someone else knows though because now I'm curious...I'm also hoping I was right about my last post.

[huguetpj]

Nope, it wont work...the computer will still tell the injectors to stay open for the same length of time and thats the problem, you'll just change the voltage going to the injector but not the pulse width which is what matters with different size injectors.

But he is talking about modifying the MAF signal. I think it would work something like the hacked MAF idea, but you need to make sure how to do this. I really don't know how the MAF circuit works, so I could be of no help. I don't think a resitor in series would work, maybe a resistor circuit or in parallel. A much better idea would be a controlled voltage regulator of some sort (or a simple high impedance amplifier) so you could separate impedances and not affect the MAF circuit. This way you could reduce the voltage the ECU sees by a simple fraction, in this case 270cc / 370cc ~ 73% or 0,73

Again this is just speculation, so care NEEDs to be taken if you wish to proceed.

[Nathan]

Oh gosh darn, that's what I get for not reading well, I thought he asked what another person did today...about putting a resistor between the ecu and injector. I think Huguetpj might be onto something. Ignore anything I said previously, it doesn't apply to the question

[huguetpj]

Jeje... anyway.. after I finished posting that I thought about something else... the ECU uses both the MAF signal and RPM measurement to set injector pulse width. So if you where to modify the MAF signal that would only be half of the equation... but since the hacked MAF works then the amplifier (actually would be a reducer) should work. And if you use a simple variable resistance to control the amplifier you could make fine adjustments with a WB setup.

The more I think about it the more possible the idea is... hmmm. Can somebody prove (or proof?) me wrong?

[tony/ka24de]

I think it is very posible, alot of people hack the mafs to make it bigger in dia so that the air being read is much less than what is going in. By using a resistor, this should do the exact same thing. I think I should get some 370 and try this. Then I could probably get rid of my fmu.

[huguetpj]

The problem with the resistor is... and I'm saying this from the top of my head since I haven't seen the MAF circuit... that you could screw the MAF calibration or something making it more difficult to setup. The ECU makes the MAF resistance maintain a stable temp, but measures V or I? Hmmm... If it's V then the amp should work and not screw up the MAF calibration. And you can buy an amp IC and use a couple of resistances to calibrate it.