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Dropping resistors.. 10 Ohm, 10 watt

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  • Dropping resistors.. 10 Ohm, 10 watt

    Local radio shack has these for a little over a buck per pack of two.
    Will these be alright to use for dropping resistors with low impedance injectors? They look alot different than what Jason shows on his website, and I'm sure aren't going to be as easy to work with, but.... These are all ceramic and squared looking and can still be heatshrunk...
    Ohms and watts is ohms and watts...right?
    I am here to help...

  • #2
    I measured the stock 88t injectors at 12.4 ohm.... the 87t injectors at 4.x ohm

    I bought 5 ohm 10 watt resistors from digikey as the 7.5's weren't listed (they are on mouser though)

    reason being is the extra ohms aren't necessary, all we are trying to do is resist enough to prevent the ecu from burning out, nothing more, there is no special sauce for the injector drivers

    since I've heard several statements that 88 ecus have worked for long periods with 87t injectors I tend to think that the difference will depend on max duty cycle, max continuous use duration and ambient temperature... as such my 5 ohm resistors will bring it up to 75% the resistance of the 88t injectors, while adding less electrical hinderance at short pulse widths

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    • #3
      I would actually be interested in measuring the injectors inductance for both types as well. Using a bench type LCR meter.

      There is another option also. There are dedicated chips that could turn the 88 PWM into 'low impedance' type PWM.
      Try not to be a Yahoo

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      • #4
        crowbar wrote: I would actually be interested in measuring the injectors inductance for both types as well. Using a bench type LCR meter.
        how accurate do you want to be? do you think fractions will help you in any way?

        crowbar wrote:
        There is another option also. There are dedicated chips that could turn the 88 PWM into 'low impedance' type PWM.
        sure, but it's probably not any cheaper or easier

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        • #5
          [quote]G-E wrote:
          Originally posted by crowbar
          There is another option also. There are dedicated chips that could turn the 88 PWM into 'low impedance' type PWM.
          sure, but it's probably not any cheaper or easier
          True. Most of those systems just use your current injector drivers to trigger a new driver inside a new ignition module box that plugs in. I've seem them for all sorts of cars.

          The only reasoning or theory behind it is that the high impedance driver with a low impedance injector is losing precision when you simply add resistors to accomplish the same current through the circuit. The high-imp (saturated) driver can't provide the instant-on current as quickly (hence the response time changes) as a low imp (peak and hold) driver can when it is driving a low imp injector. If you know anything about basic electronics and fuel systems then you can think your way through the rest of it without me having to explain.

          The end argument is you "give up" any advantage that low imp peak and hold offers, but I have yet to see any proof of this outside for people trying to sell their $200 plug-in ignition box.

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          • #6
            As far as using different resistance values I think it will make a small difference in how the injectors act at lower pulsewidths. I did a quick dyno test by doing a few runs with resistors and a few runs without resistors. The runs without resistors showed slightly richer mixtures at low rpm.load areas. I don't remember it being a big enough difference to really worry about but there was a difference. If you are using a 5 ohm resistor instead of a 6.8 ohm resistor I doubt you'll notice a difference.

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            • #7
              Has anyone ever measured the inductance of a high and low impedance injector? I guess I will since I have access to real LCR meters. And they output decimal points and numbers. Not fractions. Too funny.

              edit: I did a quick measurement of four 270cc Nissan high impedance injectors. They measured about 6.2 mH. I measured one low impedance 180cc Nissan injector. It measured around 4.4mH.

              Adding resistors alone would not make the inductance the same is my point.
              Try not to be a Yahoo

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              • #8
                Stinky wrote: As far as using different resistance values I think it will make a small difference in how the injectors act at lower pulsewidths. I did a quick dyno test by doing a few runs with resistors and a few runs without resistors. The runs without resistors showed slightly richer mixtures at low rpm.load areas. I don't remember it being a big enough difference to really worry about but there was a difference. If you are using a 5 ohm resistor instead of a 6.8 ohm resistor I doubt you'll notice a difference.
                which is exactly as I would have expected, and part of the reason I chose 5 ohm

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                • #9
                  crowbar wrote: Has anyone ever measured the inductance of a high and low impedance injector? I guess I will since I have access to real LCR meters. And they output decimal points and numbers. Not fractions. Too funny.

                  edit: I did a quick measurement of four 270cc Nissan high impedance injectors. They measured about 6.2 mH. I measured one low impedance 180cc Nissan injector. It measured around 4.4mH.

                  Adding resistors alone would not make the inductance the same is my point.
                  but the only reason to use resistors at all is to prevent the ecu frying, beyond that it is irrelevant

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                  • #10
                    crowbar wrote: I would actually be interested in measuring the injectors inductance for both types as well.
                    Inductance? You realize that is a componenents ability to induct current, in other words to produce current. I think you mean reactance, and it would vary constantly because of the change in frequency.
                    KILL HADJI

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                    • #11
                      I never knew that. Injectors can produce current? Amazing.

                      For those of you that want to know; impedance consists of resistance and reactance. Resistance is understood by most people. Reactance comes from either the capacitance or inductance.

                      Since we are speaking about electrical 'motors' (injectors are linear motors) we are speaking about the resistance and the inductance. The impedance is Z and Z is sqrt(R^2 + X^2) where X is the reactance. The reactance for an inductor is

                      Inductive reactance, XL
                      XL = 2*pi*f*L where: XL = reactance in ohms ()
                      f = frequency in hertz (Hz)
                      L = inductance in henrys (H)

                      So, yes, we measure inductance with a LCR meter. Thats how we get reactance that gives us impedance.
                      Try not to be a Yahoo

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                      • #12
                        I have had a little testing here resently on the injector resistors and various combinations. To make a statement that the resistance ONLY affects the fuelflow @ low rpm's is not correct.
                        To properly identify an incorrect part and correct part, you need to exercise the full span of the ECU meaning you need to either simulate the engine or run an engine on the dyno. The second thing you are going to need to know, is EXACTLY how your specific ECU operates. I know that Nissan did different injection schemes from 84-89 on the various boxes. I will tell you that the 84 box really is not worth the time or trouble. the 85-86 box is alright, but it to also is lacking in some of the features the 88-89 box has, like check summing the memory before the ECU shuts off. This makes for quick starts, like going to the store for milk when the engine is already hot.
                        The later boxes 88-89 have the most advanced scheme of injection for the Z31 cars.
                        The ECU operates in three modes:
                        1) idle to 3000 rpm's the unit will batch fire the injectors three injectors per bank per one revolution of the crankshaft.
                        2) the ECU after 3K then goes to one injection event on every injector per every single revolution of the crankshaft.
                        3) under high rpm's and loads, the ECU will then change the duty cycle of the injection pulse, and divide the pulse in half. Then TWO injection pulses per every revolution of the crankshaft are injected, and again the ECU can scale the fuel metering duty cycle.
                        So there is the parameters.
                        I am running a 72Lb rochester injector on my setup. The problem I am having is when the MAF reaches 4 volts, the ECU divides the injection pulse, starts injecting two shorter pulses per revolution. So what is happening to my car is that the injectors are closing to fast and as I just turn past 5K the engine starts going lean. The first time it happened, the stumble was so extreme that the AFR's went from 11.5:1 12.0:1 all the way to 18:1 or higher just like the fuel was shut off, or the ECU went into rev limiting. WRONG (and it cost me a set of pistons) but the car was not misfiring, but extremly lean.
                        So to across the board say changing injector resistors dont affect anything much is not correct. I tested 7.0 ohm resistors, and got 15:1 after we made adjustments to the latency value. I then went to 3.5 ohm resistors and improved the AFR to 13.5:1. KEEP IN MIND, the whole time I was testing, the low end was very rich 10:1 or so. The resistors do make a differance.
                        If you look at my map, you will see the line (AFR curve) rich @ idle, and up to 3K, basically the idle portion of the ECU operation, after 3K it starts leaning out until the MAF gets to 4 volts and then it really gets lean.
                        All I have to say is watch what you do when you start changing out resistors because they do change the operation of the ECU, and you need to know exactly what to look for or you will screw up the AFR'S at different loads and enging rpm's
                        Oh and BTY, if you want to you can run WITHOUT the resistors on the low resistance injectors if you want. I have tested, and the calculations of the current through the drivers and they are rated at high enough current to not be a problem. You have to keep in mind, that even @ 100% duty cycle, the injectors are only on for a few milli seconds, hardly enough time to create high current problems.
                        anyway, I have to make mods to the ECU and then we will see if I am able to run the box. There is ONE other option for me, go with the M30 box. The ignition is the same as the z31, but the change was in the injector drive, Nissan made that box fully sequential for the injectors, so that may be an out for me, but the connectors will have to be adapted to the M30 main connector. anyway.

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                        • #13
                          From the simplest circuit analysis standpoint, adding a resistor before the injector will decrease the voltage drop across the injector. This might increase opening times and decrease closing times.

                          Its not just current limiting we are talking about here. Voltage plays into this also. The injectors are solenoids which are very similar to electrical motors. The 'solenoid' needs a higher voltage to get it to initially open. Once open, it can be held open with a lower voltage.

                          From what I suspect, you could monkey the hex-code to adjust one spectrum of the rpm range but the other would enrichen/lean out.

                          From a circuit analysis standpoint, its actually a patallel situation as far as the voltage at the top of the injectors and each bank firing. At higher rpms, both banks (all injectors) are firing and in a parallel situation.
                          Try not to be a Yahoo

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                          • #14
                            Dan-TSS wrote: Local radio shack has these for a little over a buck per pack of two.
                            Will these be alright to use for dropping resistors with low impedance injectors? They look alot different than what Jason shows on his website, and I'm sure aren't going to be as easy to work with, but.... These are all ceramic and squared looking and can still be heatshrunk...
                            Ohms and watts is ohms and watts...right?
                            To answer your question; I would use 2 of these in parallel to get 5 ohms equivalent. This also reduces the power through each one by the way.

                            But to answer your question, you need to know what is the tolerance on these?
                            Attached Files
                            Try not to be a Yahoo

                            Comment


                            • #15
                              [quote]crowbar wrote:
                              Originally posted by Dan-TSS
                              Local radio shack has these for a little over a buck per pack of two.
                              Will these be alright to use for dropping resistors with low impedance injectors? They look alot different than what Jason shows on his website, and I'm sure aren't going to be as easy to work with, but.... These are all ceramic and squared looking and can still be heatshrunk...
                              Ohms and watts is ohms and watts...right?
                              To answer your question; I would use 2 of these in parallel to get 5 ohms equivalent. This also reduces the power through each one by the way.

                              But to answer your question, you need to know what is the tolerance on these?
                              but if he does that he can get away with 4 of them, two per bank, assuming the correct harness mods

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