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Dropping resistors.. 10 Ohm, 10 watt

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  • #16
    He would have an equivalent 5 ohm 20 watt resistor above the 3 paralleled injectors. If the 3 injectors are around 2.4 ohms, we are very close or over the power rating. In parallel, they are about 0.8 ohms. So more than 2 amps is flowing. But I bet it would work.

    But we still have a situation where a majority of the voltage is dropped before the injectors.

    There is a very cheap way to correct this. Have a capacitor with its + side 'noded' between the 'top' of the injector bank and the 'bottom' of the two 10 ohm resistors (that are paralleled). Its - side goes to ground.

    As I understand it, the actual switching takes place under the injectors and then to ground.

    So the capacitor will 'load' 12 volts through the two power resistors and then 'fire' the 12 volts when the transistor connects the bank to ground. This 12 volts provides the initial snap for the injectors. The 'battery' 12 volts provides the following holding current (which is at a lower voltage when the transistor is on). Once the transistor goes off, the capacitor is again seeing 12 volts through the top end (it charges as a RC circuit). We could even fly-back the injectors back emf to help charge up the capacitors. This even closes the injectors faster.

    Very cheap and neat.
    Try not to be a Yahoo

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    • #17
      i used those same exact ones on my 84 with an 88 computer. seems to work fine.

      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?

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      • #18
        Sorry about that size there. Injectors are modeled by R1/L1, R2/L2, and R3/L3. I did not put all the values in yet. B1 is the car battery and ECU is should also be 'containing' the Q transistors. Its a quick sketch now.

        R4 and R5 are the power 'current-limiting' dropping resistors. They also drop voltage. C1, capacitor, restores voltage at the 'top' of the injectors. The zener protects the circuit from over voltages.

        There is a 'fly-back' in that when the transistors (Q) open, the collapsing magnetic field in the injector inductance feeds back upwards towards the capacitor, charging it and 'resetting' the circuit. The zener will bleed down any spikes. I will look at the individual circuit values later. This is just the concept.

        I would strongly suggest that this inexpensive concept be pursued for those of you running low impedance injectors with 88+ ECU’s. Note that the point to this circuit is to decrease opening AND closing times on the injectors. That is what injectors should be. Open or closed.
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        • #19
          but it would have to be a small enough capacitor so as not to keep spewing voltage beyond the minimum pulse used, and the bigger the injector the smaller the minimum required

          actually looking at the diagram, how is the cap supposed to charge if the injector isn't grounded, and likewise if both leads to the cap have no potential (both 12v)?

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          • #20
            G-E wrote: but it would have to be a small enough capacitor so as not to keep spewing voltage beyond the minimum pulse used, and the bigger the injector the smaller the minimum required

            actually looking at the diagram, how is the cap supposed to charge if the injector isn't grounded, and likewise if both leads to the cap have no potential (both 12v)?
            Yes the values of the cap and zener diode need to be chosen. But I do not follow your logic. You seem to imply that a capacitor that had charge on it could control the transistor below? You should know that the Q are transistors and that the ECU turns them on and off?

            So once the Q is turned off, so what if the capacitor has a charge on it? Maybe I am not understanding what you are saying?

            The capacitor would charge through the power resistors when the Q is off. And also through flyback from the inductor.
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            • #21
              The sizing of the zener is trivial. The sizing of the capacitor(s) would require an analysis of how a low impedance ECU switches the low impedance injectors.

              From what I understand, the 84-87 ECUs have an initial pulse followed by a series of pulses. the series of pulses 'tickle' the injector to just maintain an open state (this limits the current also). The critical thing to find would be the minimum amount of charge to open the three injectors. This would allow the most efficient operation I believe.

              The low impedance systems actually use PWM within a PWM scheme then!

              A general run through of how this mod works is as follows...

              1. Q's are open (they are all on and off together right?)
              2. 12V is then on across the top of the circuit. That means it is 12V potential and the cap has 12V on it.
              3. Q's close allowing current flow.
              4. Cap discharges first. It provides the initial voltage/current to overcome the injectors impedance.
              5. Current flowing through the power resistors then provides the holding current to keep the injector open. A small amount of charge also charges the cap but NOT to 12V!
              6. Q's close. Current stops and magnetic field in injector collapses. It shoots its charge back up the circuit into the node above.
              7. Zener lets any spikes blow through to ground.
              8. Cap captures the rest that is below zener voltage level.
              9. Cap also will charge as a RC circuit through power resistors.
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              • #22
                This is the ebay response I recieved from someone trying to sell 300zx injectors...

                You have zero trust in the Z31 community.
                Please don't start an argument with me about something that I'm selling. I've seen how you act on z31performance.com with the flow testing that Jason did. Also, why would you bid on something that you are unsure about? The side feed injectors are high, and the top feed are low. I know this through other people's experience with Z31s. Trial and error with this car, and not everyone has to learn it like that. Z31 car owners read the forums to gain knowledge to learn how to solve there own problems, so frying an ecu doesn't occur, and that's what will happen when you start mixing and matching. A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law.
                I'm sure I could figure out the injector impedance, but there would be no need.
                Amazing how sure they are that they can figure things out. Except saying you can do something, and doing it is not the same thing.

                I am very sure side-feed injectors are NOT always high impedance.
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                • #23
                  double
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                  • #24
                    crowbar wrote:

                    I am very sure side-feed injectors are NOT always high impedance.
                    And I have a very nice shiny set of brand new side (well, dual) feed sitting right here to prove it. These were sold as "88-89 Turbo" injectors, they have a center plug and ohm out to about 2.6 each. They are actually 87 Turbo injectors.....

                    Jason

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                    • #25
                      amen
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                      • #26
                        [quote]Spdstr280Z wrote:
                        Originally posted by crowbar

                        I am very sure side-feed injectors are NOT always high impedance.
                        And I have a very nice shiny set of brand new side (well, dual) feed sitting right here to prove it. These were sold as "88-89 Turbo" injectors, they have a center plug and ohm out to about 2.6 each. They are actually 87 Turbo injectors.....

                        Jason
                        or 86T, because both 86-87T have low-imp side feeds.
                        Attached Files

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                        • #27
                          yes like I said plenty of times, 87T side feed low-imp.... 88+ side feed high-imp

                          and I tested the 87t at 4.8 ohm and the 88t 12.4 ohm

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                          • #28
                            [img]a href=[/img][/img]
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                            • #29
                              *Update..
                              This circuit might be something for someone to be concerned with if using these exact same resistors and merely doing a stock ecu to stock ecu swap.
                              ~I have not seen any issues using these resistors when tuning with Nistune, but understand the point Crowbar is stating.

                              I believe that when using Nistune, the difference can be adjusted with the "PreIgnition Time table"(injector latency). I say this because I am using moderately larger than stock injectors(500cc/min) and am able to adjust everything to where it idles and part throttles beautifully.

                              ^^In conclusion....I'll pass on the worries/concerns about the resistors until I see a valid result that shows me that it isn't working right.(which should be fairly obvious below 2500rpms..in regards to these effecting the opening and closing of the injectors as the ecu expects)

                              Dan 8)
                              I am here to help...

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                              • #30
                                Dan-TSS wrote: *Update..
                                This circuit might be something for someone to be concerned with if using these exact same resistors and merely doing a stock ecu to stock ecu swap.

                                ~I have not seen any issues using these resistors when tuning with Nistune, but understand the point Crowbar is stating.

                                ^^In conclusion....I'll pass on the worries/concerns about the resistors until I see a valid result that shows me that it isn't working right.(which should be fairly obvious below 2500rpms..in regards to these effecting the opening and closing of the injectors as the ecu expects)

                                Dan 8)
                                The intent is for people using 88+ ecus with 87- injectors.
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