Low impedance injectors & tuning issues.

[Edub1]

A closer look at injector impedance might suggest that simply adding a resistor pack to low impedance injectors might not have the exact effect of making a peak hold type function like a saturated type. I have tried this and have been having crazy fueling issues with my ROM tunes. I'm not saying it can never work - just that it might be hit or miss. This might be the reason that so many of us with the popular rx7 460cc injectors might be having problems.

Impedance

Injector impedance describes the electrical resistance of the solenoid windings. These are usually grouped in two categories:Low and High resistance.High resistance (> 12 ohms) injectors are used where only one injector is driven by one driver, as in most True Sequential Fuel Injection applications.Most of the 500cc and larger injectors available are Low Impedance. LOW (1.7 - 3.0) ohms OR Peak and Hold DriverHIGH (10 - 16) ohms OR Saturated Circuit Drivers These type of injectors and drivers may also be called current sensing or current limiting. They are more expensive and complex than saturated circuit drivers, and are not generally used with domestic production ECUs. They are primarily used in aftermarket high performance systems. Most high flow injectors are low resistance (2-5 ohms) and use a peak and hold driver to activate them. The Peak current is the amount required to quickly jolt the injector open, and then the lower Hold current rating is used to keep it open for as long as the ECU commands. These require the extra kick from the higher current to keep the opening and closing time of the injector stable at the higher fuel flow rate. With this type of driver, 12 volts is still delivered to the injector, but due to the its low resistance, the current in the driver circuit is high. How high? Using Ohms’s Law we can calculate the current rating (12v/2 ohms = 6 amps). This is substantial current flow and a Saturated Injector cannot handle it. The drivers also come in two values; 4 amp peak/1 amp hold, and 2 amp peak/0.5 amp hold.. Even though 6 amps may be available to operate the injector, the maximum it is allowed to reach is 2 or 4 amps, depending on the driver’s current limit.

Most domestic OE production EFI systems use an ECU with 12 volt Saturated Circuit drivers. These are very inexpensive, simple, and reliable. This type of driver works by supplying 12 volts to the injectors and the ECU turns it on and off to establish a fuel injector pulse. In general, if an injector has a high resistance specification (12-16 ohms) the ECU uses a 12 volt saturated circuit driver to control it. This means that the current flow in the driver and injector circuit stays low keeping the components nice and cool for long life. Conversely, a downfall of a Saturated Circuit driver is that it has a slower response time (and closing time) than a peak and hold type. This slower time can somewhat decrease the usable operating range of the injector energized by this driver. An injector operating on a saturated circuit driver typically has a reaction time of 2 milliseconds while a peak and hold driver typically responds in 1.5 ms. There are some exceptions to this, notably the Bosch 803 injector used on the Porsche 944 turbo which is 4.7 ohms. Most manufacturers have used both types at one time or another. The trend lately is to use high impedance types in most production cars. The best way to determine impedance is to put a digital ohmmeter across the two electrical connections and see what it reads. The primary advantage of low impedance injectors is a shorter triggering time. When large injectors are fitted to high output engines, low impedance injectors will often give a better idle quality because of this fact. The primary advantage of high impedance injectors is the fact that less heat is generated in the drive circuit and often no external resistors are used.

[Edub1]

Nobody has any input on this issue???

[turbo2nr]

i cant rember too much about the rom tuning things but form what i recall, dont you have to do some conversion with the binary code used for the injectors to make the work with the low impedance...

just a taught still not to sure when i get home ill read up again on my rom tuning notes..

[Edub1]

Well, I just poped for a new set of RC 550cc saturated injectors becuase I really need them anyway. We'll see what happens.

[GTR PrYdE]

Well, I just poped for a new set of RC 550cc saturated injectors becuase I really need them anyway. We'll see what happens.

Back from the dead, but a ton of good injector info!Chime in if you run topfeeds, and how you did it!

I recently made the switch to TopFeed Evo 560cc injectors with 10ohm/50watt resistors inline with each power wire, and I got a rom tune, and after 2 revisions, the car still runs pig rich, and erratic when being revved.

Now I still haven't found out if it's the tune or the injectors that are giving me hell, but this thread really opened my eyes, seeing my setup was hit or miss, and might have "missed"

I'm suprised no one really had anything to say...

Maybe now?

[ShopliftTHIS]

so what if we're running the rx7 injectors with no tuned ecu and just a safc? we still gonna have problems?

[WDRacing]

I dunno why you guys don't just get the proper injectors to begin with...

Not trying to poke you guys in the eye, but unless you need to run HUGE injectors, then get high imps and call it a day.

WD

[Miller White]

well that doesnt help. if we dont have a tune and we're gonna run rx7 injectors can we do it with just a safc?

[WDRacing]

well that doesnt help. if we dont have a tune and we're gonna run rx7 injectors can we do it with just a safc?

Well it depends on year/model of the injectors since some were high imp. You'll need a minimum of the SAFC and the resistor pack, then you'll need to tune them via wideband.

My comment was aimed at the guys using alternative tuning, like the MS or the rom tune. It's easier to just use the high imp injectors, they aren't more expensive, they are readily available and match the current 240's setup.

I've never heard of anyone having issues with low imp injectors though, but most are tuned via standalone.

WD

[eazye2000]

I was just searching for this stuff the other day. Mike helped me out a little bit, but I'm still on the fence about it. I was told 10ohm/10watt resistors, but 50 watts should be plenty of headroom.They don't make very big high impedance injectors. Or at least I haven't found any. And with the low impedance stuff, I've been finding a set of 8x, 800+cc injectors for like 200-250 brand new.

Does anyone have a good website for injectors? Like, high and low impedance? I'd like to get a good variety to look at and compare.

[Miller White]

If i use stock sr20 370 injectors would i need to worry about any of this stuff lol?

[GTR PrYdE]

If i use stock sr20 370 injectors would i need to worry about any of this stuff lol?

No.

[GTR PrYdE]

I was told 10ohm/10watt resistors, but 50 watts should be plenty of headroom.

I got my resistors from JGS, and have read alot about 10ohm's being correct, however-

On the JWT site, they sell 6.8ohm/10watt resistors... which confused me a bit... That's the only time i've read of different ohm's for injectors

WD- At the time, it seemed like a nice cheap switch- resistors-20 bucks, top feed rail- 40, evo injectors- 100, pigtails- 10...

But I probably could have found a good set of 560cc sidefeeds for the same price ...

[Miller White]

Well i have my safc hooked up in my car now. no turbo and stock injectors. i can up the fuel by like 50 percent and it wont do ****. i know it should at least bog the car down in what ever rpm range the fuel is up'd in. i know it has to be hooked up half way right cause i can change the sensor type and the in and out and it'll affect the car. any ideas?

[eazye2000]

Miller, Do you have a wideband you are checking for any air/fuel ratio changes? If you don't, I wouldn't suggest even playing with an SAFC. That's a recipe for disaster. Not saying you're a newb, but 9/10 people who play with SAFC's end up blowing/popping something.

If I get a deal on another SAFC, I'll throw down the cash for some injectors, and a rail and play with my S14 to see how everything reacts. I can afford the downtime, so no biggie.

[nissanfanatic]

You can't expect to simply install a resistor between the injectors and drivers and have the function of a low impedence injector. The entire setup must be oriented towards low imepence function. IIRC, even the plug and play AEM EMS can't support low impedence injectors without the resistors. All you are doing is simulating the same load as stock on the driver by putting a resistor in line. With high impedence setups, more voltage has to be present with less current to open the injector. A low impedence setup can be driven with less voltage and more current. Looking at this problem relatively, you can operate a sprinkler with flow or pressure. Flow is more readily available if the hose is already full of water. Pressure on the other hand may have to build. Voltage can be related to pressure, whereas flow can be related to current flow. By installing the resistor inline, you still have to have the same amount of power as before to overcome the resistance. You don't get the added benefit of response that you should with low impedence resistors.

This thread has nothing to do with SAFC/370cc injector setups. You should start your own thread.

[eazye2000]

This thread has nothing to do with SAFC/370cc injector setups. You should start your own thread.

Eh, what?

I hope that wasn't directed towards me. If you're talking to Miller, he said he's got stock injectors he's been playing with.

I was merely stating that 'if' I get another SAFC, I will play with a set of low impedance jobby's and let people know what I find out.

I don't hop in here with some scientific theory, and confuse people. I 'do', and have a hands on experience so I can share with peoples. Sorry, but that's how I do.Some people have had really good luck with peak and hold injectors, with an add-in resistor. Some, not so much. I believe that's what we are trying to figure/straighten out here.

My apologies if I misunderstood you. Fanatic, your posts always come across, to me, as arrogant. And I hope that's just the lovely world of internet forum talk misinterpretation.

[Bernard]

The main thing you need keep in mind is that the latency of the injector is different from the manufacter will have specified. After you've adjusted the kvalue and latency, tuning will be as per usual. Basically it' s a non issue.

[GTR PrYdE]

You can't expect to simply install a resistor between the injectors and drivers and have the function of a low impedence injector. The entire setup must be oriented towards low imepence function. IIRC, even the plug and play AEM EMS can't support low impedence injectors without the resistors. All you are doing is simulating the same load as stock on the driver by putting a resistor in line. With high impedence setups, more voltage has to be present with less current to open the injector. A low impedence setup can be driven with less voltage and more current. Looking at this problem relatively, you can operate a sprinkler with flow or pressure. Flow is more readily available if the hose is already full of water. Pressure on the other hand may have to build. Voltage can be related to pressure, whereas flow can be related to current flow. By installing the resistor inline, you still have to have the same amount of power as before to overcome the resistance. You don't get the added benefit of response that you should with low impedence resistors.

That makes alot of sense, but why is this the first time i've read this?!

LOL I would have never made the switch if I had known

Thanks

[WDRacing]

HE was talking to the dude that doesn't need to be posting in this thread. You were just answering the dude...that needs to make a new thread. Since high imp 370 injectors have nothing to do with low imp injectors and tuning.

Everyone needs to relax...

Low Imp suck unless you need 100lb injectors...like I already said. If you have them...sell them. Buy what the ECU is set up for...

WD

[nissanfanatic]

Low impedence injectors are very good for performance applications if the ECU is capable of driving them. If you use them on an ECU configured for high impedence, then you will simply insert a short essentially, unless you increase the load with a resistor. Agreed, just use high impedence injectors for stock ECUs. If you need to use low impedence injectors, then you should probably be looking into an ECU that has drivers designed for low impedence injectors. And before someone says AEM EMS, no, not unless you buy the universal box.

[WDRacing]

Exactly...there are high imps available for cheap up to 72 lbs which is more then 85% of the people can fully use. I'd never go low imp unless they of course came with the car or I needed 100lbers or better.

Cheap parts rarely work out for people, especially when fuel is concerned.

I love guys that try to boost a 240 for 1200 bucks...more power to ya. But $3500 is a much better budget to work with and it will give long lasting results.