280 ZXT injectors - LOW or HIGH impedance?

[Mudge]

Many of the injectors used for replacements I see talked about are low imp, are the stock injectors low or high imp?

[SleeperZ]

Low impedance. Stock ZXT injectors are about 2.2 ohms, most of the higher flowing injectors are low impedance. The reason is low impedance injectors activate faster, making them more useful over a higher range of on-times. For the same flow rating a low impedance injector will idle better than a high impedance one.

[Mudge]

Right, I knew that stuff, just didn't know what "we" had Most of the turbo/blown cars come low impedance stock, pretty hard to find high impedance stuff past 50#, and they aren't as great on the idle side for many cars.

 

Thanks

[Mudge]

Something I forgot, how are you putting O ring style injectors on the car... Getting a custom fuel rail?

[z-ya]

SleeperZ wrote:

Low impedance. Stock ZXT injectors are about 2.2 ohms, most of the higher flowing injectors are low impedance. The reason is low impedance injectors activate faster, making them more useful over a higher range of on-times. For the same flow rating a low impedance injector will idle better than a high impedance one.

 

The stock ZXT injectors are 2.4 Ohm as meausred on a precision 4.5 digit DVM.

 

I don't agree with you regarding activation time and idle quality. If the ECU's output drivers are setup correctly, high Z injectors will respond just as fast as low Z injectors. As far as idle quality, the impedance of the injector has nothing to do with it. My truck has high Z injectors, and it idles super smooth. What does determine the idle quality is the flow rate vs the fueling resolution of the ECU. If the resolution is not fine enough to deliver the proper fuel, it will idle poorly regardless of injector impedance. An example: if the engine required a 1.5ms open time to idle smoothly, but the fuel computer's resolution was to the nearest ms, then it would either idle rich, or lean. You wouldnot be able to find the optimal setting. I know this because I have low Z injectors in my turbo Z, and the idle is border line because the fuel computer I'm using does not have fine enough resolution.

 

Pete

[SleeperZ]

Mudge - I am not using O-ring injectors. I tapped my fuel rail for 5/16" hose barbs, and converted my 370cc injectors to 5/16" hose.

 

Z-ya - I agree that ECU resolution can affect how well a certain injector can be controlled. Most stock ECUs can probably not control a higher flow injector well, and that could be the root of most idling issues with a higher flowing injector.

 

Peak and hold (ie: low impedance) injectors can fundamentally be operated faster, resulting in a potentially wider range of operational duty cycle. A low impedance injector is nailed ("peak") with a high slug of current to open it quickly, then the current is reduced to hold it on. Setting up the magnetic field to induce movement in the injector is very slow - a high initial current helps it along. Once the injector is open you can reduce the current to "hold" it open. If the injector current is not scaled back, the injector will burn up. A high impedance injector cannot be overdriven like a low one, and cannot be opened as quickly.

 

Perhaps the newer technology high impedance injectors can operate as fast as the low impedance ones now, but that certainly was not the case when the L-jetronic was developed.

[Guest Anonymous]

Not to be argumentative, but only some of what you say here is true. It is true that the ECU resolution can have a lot to do with how well a car will idle, but the statement that low Z injectors don't have a shorter open time is not necessarily true. With all factors equal, a low Z injector using a Peak/Hold driver will be able to lift the valve open in a shorter time then a high Z injector. This is because the initial current is higher and will saturate the injector coil in a shorter time. Once the coil approaches saturation the current is then clamped at a lower rate in order to hold the injector open. This will not hold true on low Z injectors when you are using current limiting resistors. At that point you basically have high Z injectors or at least higher Z.

 

The difference in opening time is most significant at idle since the open time is smallest and the lag time is the highest percentage of open time. As the ECU generates a 1ms pulse the ECU has no idea on how long the "lag" time is. In reality the injector may only be open for .85ms since .15ms is taken up by this lag time. In some critical situations where the injector pulse width is very short, because of... say the use of large injectors in batch fire mode, then the impact of lag time may be the difference between a good idle and bad. Many ECU's don't do well with injector times less the 1ms. Much of this depends on how large the injectors are, what the required minimum pulse width is and how little margin you have between minimum resolution and actual injector duration. This is even more aggravated if, as you stated, the ECU resolution is poor.

 

Much of this has to do with the injector driver circuit and how well other factors, such as fly back, are taken in account for. Injector closing times can also effect idle since the large coil inductance on high Z injectors need more time to dissipate the large EMF generated by the collapse of the coils field. This would keep the injector open longer then expected. This action is also some what erratic.

 

In general, low Z injectors tend to be more stable at low open times, if paired up with a properly implemented Peek/Hold driver.

 

Just my $.02

[Mudge]

I know that on the LT1 stuff, guys running 50# high imp injectors dont have the best low end, sometimes thats guys running lots of injector though with future plans, 1ms just gives them too much fuel.

 

I thought about running hose to O ringed setups, but was not really sure that doing so with 40-50 psi was a great idea. How are you keeping them sealed? Anyone have a guess as to how much the stock rail will support HP wise, effectively?

 

Thanks all

[Mudge]

Many ECU's don't do well with injector times less the 1ms.

 

I've never even seen less than 1ms on an LT1 computer (as the only example I can provide, sorry), so I assume it does not exist, and in stock form with 2-4ms with stock injectors/power levels it wasn't needed. I suppose it could just be that it can't display in log output less than 1ms, but I assume it is just plain not possible.

[z-ya]

I was assuming that series current limiting resistors would be used with the low Z injectors. Well, you know what happens when you assume. I agree, a sided by side comparison without limiting resistors, would in fact show that the low Z injector has a fastewr response (opening) time.

 

The 1ms I was using in my example was just that, and example. My car idles with a 1.2ms opening time.

 

Pete

[Guest Anonymous]

I use RC's 550cc low Z injectors in batch mode on my L28 6 cylinder. At idle I have around .98ms of injector time. That's with 3 injections per cycle with all 6 fired in batch mode. This gives me around a 13.5:1 AFR. If my ECU could do full sequential on a 6 cylinder, I would have opted for sequential injection instead. That would have given me much more margin on injector times. Looks like I'm going to have to make the step up to the Haltech E11 someday. Now that's an ECU. Best bang for the buck in my opinion. Too bad Haltech support is so bad here in the US. Maybe someday they'll get their act together.

[z-ya]

I'm running Bosch lowZ 380cc/min injectors in batch mode. I'm using a Wold 3D v3.0 computer in my car. Made in Austrailia like the Haltech. The only issue I've had is with the idle after going with larger injectors. With the stock ZXT injectors it idled real smooth. It's kind of got a little lump in there now (not too bad, but noticable). Off idle it roars. These L28ETs sip the fuel at idle.

 

The Wolf has a global fuel scale adjustment, so you can set the injector opening time range. So you guestimate the opening time at WOT/full boost, and set the fuel scale about 10% more for a little head room. This gives you the maximum tuning resolution.

 

Pete

[SleeperZ]

I know that on the LT1 stuff' date=' guys running 50# high imp injectors dont have the best low end, sometimes thats guys running lots of injector though with future plans, 1ms just gives them too much fuel.

 

I thought about running hose to O ringed setups, but was not really sure that doing so with 40-50 psi was a great idea. How are you keeping them sealed? Anyone have a guess as to how much the stock rail will support HP wise, effectively?

 

Thanks all[/quote']

 

I modified the SVO 370 cc injector by hacking off half the plastic surrounding the o-ring (just like Scottie-GNZ documented years ago) - that gives the full width of a Nissan FI hose clamp's worth of material to clamp. I haven't run them at full pressure yet, but no leaks there (the fuel filter is another story ).

 

I ran 300hp or close to it (14 psi boost, stock FPR) on the stock fuel rail. I have no idea whether it was limiting me, or how much more you can flow. On my new setup, I plumbed AN -6 lines throughout, but I am still using the stock lines from the tank - we'll see how that works...

 

Z-ya - it sounds like we are on the same page. Yes, by using a current limiting resistor with low impedance injectors, you are defeating the benefit of the low impedance. You need a proper peak-hold driver, or on a saturated setup you can jury-rig an RC setup to hit the injector with full voltage, then bleed it off to about 1/3 voltage (say a 100uF capacitor in parallel with a 5 ohm resistor, all in series with the driver).