Rpeck

I want to now upgrade my primary injectors to 720’s. My stock Harness and ECU uses 12-13 Ohm. High impedance injectors. I can only get 2-3 Ohm low impedance injectors in 720 CC. Are you with me so far? That’s the simple part.

Now, if I ohm out a low impedance injector with nothing connected it will read 2-3 Ohms. My ECU is looking for a 12-13 Ohm signal. People say wire in a 10 Ohm resistor on one of the injector wires, right? (still with me?) A resistor LOWERS a signal, it does not raise a signal .. so if I have low imp injectors and put on a 10 ohm resistor how is my ECU going to see those as High imp injectors.. I will be lowering the siganl even more. This is making no sence to me at all. Can someone please clarify this?

Also where do I wire in the “part or resistor” I need to make this all work? At the ECU .. or on the injector wire itself? Also what “part” am I looking to get .. anyone have a exact description & or part number and place of purchase?

Another thing... am i going to have to butcher my wiring harness? don't the low Imp injectors have a different Plug? Do I have to wire in new plugS?
Thanks a lot,


Robert

AreExSeven

Not totally familiar either, but I think the signal goes the other way.

I read it as the resitance is always 12-13 OHMS on the ECU, and the resistor changes the resistance on the injector to be lower (ie 2-3 OHMs) to match the impedance of the injector.

I could be totally wrong though

zyounker

it lowers the single but will increase the resistance (ohms) put it at the injector.


Get it?

zyounker

high impedance injectors use less single then low inpedance injectors.

RETed

You need to take a basic course in electronics.

Resistance in series is additive.
Resistance in parallel is the inverse of the sum of their inverses (confuse yet?).

Bottom line, if you add a resistor "inline", then you add the 10-ohms to the 3-ohms of the fuel injectors, creating a 13-ohm nominal resistance.


It'll be easiest and safest at the ECU leads.&nbsp Trace the leads for each fuel injectors, as labelled in the FSM.&nbsp Cut the wire at the ECU (leave a little wire on the plug) and just connect the two ends to the cut wire ends.&nbsp That should basically be it.&nbsp Get the "sandblock" resistors that are at least 10 ampere rated.&nbsp Radio Shack (or any electronics store) should be able to get these or order them for you.



-Ted

AreExSeven

Ya thats what I meant to say

A resistor does not lower the resitance, it raises resistance. Hence the name.

If you check the resistance of something, and it is 2-3 ohms, and you wire in a 10 ohm resistor, it is going to resist even more, making it 12-13 ohms.

Its basically like it takes a signal in one side, and resists it going through to the other side, make more resitance. If that makes sense.

Rpeck

Okay I added this part of my question in a edit. Can anyone comment on this?

That other stuff is making more sense now, thx fellas & Ted

RETed

If you're running high impedence fuel injectors originally, yes, you need to cut (i.e. "butcher") the wiring harness.

If you are running low impedence fuel injectors originally, the 720's should plug right in.



-Ted

Rpeck

]

Ya i was thinking about that backwards.. only 1 cup of coffee so far today. It makes alot more sense now. I think I was thinking of a capasitor or somthing .. I have used capasitors on smaller speaker in stereo systems to limit the bass siganl to them .. to prevent distortion .. my confusion is clearing up.

AreExSeven

Not sure if they have different plugs, but if you need em I've got a few from base model 86-87's sitting around that I pulled from the Jyard. Lemme know.

RETed

Capacitors (and inductors) still adhere to the resistance rules - see above.&nbsp Capacitance and inductance are a whole different ball game though.

And that was your Electronics 101 lesson for today...



-Ted

Rpeck

I assume I can get the propper plugs at any parts store? Or are they special order? what would I call them if I was to call around local places to ask if they carry them?

Thx again

RETed

I believe GReddy sells them.&nbsp If not, tell them you need plugs for "ND" or "Nippondenso" fuel injectors - that should help.


-Ted

Rpeck

Are they in good shape? I might just take you up on that offer .. if you don't need them. I will cruise up there and we can swap a few stories. I will drive the AE. Assuming I find my small oil leak tonight... with football, & baseball playoffs I have been slacking on my car work

damn sports.

AreExSeven

Well, heres one. You can judge the shape. I can't find the other one right now (damn parts are all over the place), but it is in similar shape.

Rpeck

Is this the resistor I need?

http://www.radioshack.com/product.as...5Fid=271%2D132

J-Rat

iTrader: (2)

Actually RETed, resistance in parallel is the sum of total resistance divided by the number of resistors in parallel.

If you have two 6 ohm resistors and a 3 ohm in parallel, the total resistance is 5 ohms... Resistance in a series is the sum of all resistors. Or in this case, 15 ohms.

Funny thing is, that if you have 12V on one side of EITHER of the aforementioned circuts, you will have 12 V on the other side. All the resistance does is impedance match the signal source to the signal destination.

If your ECU needs to see 13 ohms, and you put a 3 ohm load on it, the amperage generated could be enough to blow the ECU.

Rat

Rpeck

Thats the idea of adding the 10 Ohm resistor right? You anwsered nothing J-Rat. Will this work? and will that resistor I linked to work?

thx

J-Rat

iTrader: (2)

Actually, I was trying to show RETed that there is a much simpler equation for figuring out resistance in parallel.

The idea of adding a 10 ohm resistor to a 3 ohm injector, is so that the ECU sees 13 ohms of total resistance. This keeps the signal amperage inline with what the ECU is rated for. So, theoretically? It should work. Now here is the problem....

Most resistors are rated in wattage...This is the amount of amperage that they can disappate (turn into heat) without burning up. So how many amps are the resistors handling in order to impedence match? In the FC, I dont honestly know..I would need a schematic of the resistor network in order to answer your question.

Now here is the good news. The link you provided was to a 10 Watt resistor. Not a small resistor by any means, and may be just what you need. If you go too big on the resistor wattage, guess what? It will work just fine...If you go to small? It will burn up.

error on the side of caution.

Rat.

(hope that is more informative..)

Felix Wankel

I bought every ******* 10 ohm resistor that Radio Shack had. You know what worked?

The stock ones off a pre-87.5 car. Irv, (Keith's dad) says they are ~7 ohm resistors. The wattage I don't know.

I got just a wee bit fed up with soldering and desoldering in my wiring harness that I ripped a resistor pack off my brother's 86 GXL and it worked flawlessly after a little rewiring.

J-Rat

iTrader: (2)

And it just so happens that....

I have a spare resistor pack lying around..

Rat

mac_dad6

how do you know if your primaries and secondaries are high or low impedance

mac_dad6

also, what do the resistor packs look like and where are they located

Rpeck

Do you want to sell that pack?

Rpeck

Does this mean the radio shack resistors would not work for you? What did it do, or not do?