Saturated vs Peak & Hold Injector Drivers

[SA]

Some of you may be wondering what the difference is between high and low impedance injectors.  High impedance injectors are used with Saturated Drivers.  Low impedance injectors are used with Peak and Hold Drivers or with Saturated drivers when used in conjuction with a ballast resistor (resistor box).  The following, taken from SAE J1832 Nov 1989 - Gasoline Fuel Injector, defines each method and also lists the advantages and disadvantages to each.

SA

Injector Driver—An electronic circuit that supplies voltage pulses to an electromagnetic fuel injector for a precise increment of time and at a given repetition rate. The accuracy of these pulses and their repetition is
normally ±0.001 ms. The peak-hold driver and the saturated driver are most commonly used by the industry for vehicle applications.

PEAK-HOLD DRIVER—A driver that uses two levels of current to operate the injector. The driver circuit applies battery voltage to the injector until a predetermined current level is reached. The current is then reduced and held at a lower level for the duration of the PW. This type of driver is normally used with injectors having low resistance coils (typically around 2 ohm). The accuracy of the driver peak current level (Ip) and the hold current level (Ih) is held to ±0.50%.

Advantages—The high peak current minimizes OT response and the low hold current minimizes CT response. This method of control results in an increased linear range of injector operation.

Disadvantages—Heat is primarily dissipated at the driver. Circuitry is more complex than that of the saturated driver.


SATURATED DRIVER—A power transistor driver that turns fully on for the entire duration of the injector PW. This type of driver is used with injectors having high resistance coils (typically 12 to 16 ohm) or with
injectors having low resistance coils in combination with a ballast resistor.

Advantages—Heat is primarily dissipated through the injector or ballast resistor and not at the driver circuit. Circuitry is simplified compared to the peak-hold driver.

Disadvantages—The inherently slower dynamic response of this system decreases the injector’s usable flow range. The Q of an injector used with this type of circuit is more duty cycle sensitive due to heat dissipation considerations. This driver’s inductive suppression, which may be resistance, capacitance or zener, significantly affects the injector’s Qd rates due to variations in the circuit’s current decay rate. This decay results in a change of the injector’s closing time.

[quick50]

Thanks Scott.


Steve

[BLKMGK]

FWIW - on a Mustang I setup with 30lb Ford injectors on an old DFI years ago I used to have issues idling. I had always thought that the issue was that I didn't have P/H injectors\drivers since when I went down past a certain point it just ran crappy. Above that point it smelled rich

When I setup 72lb P/H injectors with a resistor pack on my Supra I wondered if I'd be able to idle these suckers down far enough. Wow, I sure can! In fact I've spoken to guys idling down 1000CC injectors down just fine too. My car idles stable at 800RPM, A/C doesn't hurt stability either.

I don't miss the AEM not having P/H drivers. The resistor pack doesn't seem to screw up the ability to idle big injectors way down, they seem to remain stable. I can only imagine that my old DFI just didn't have the resolution or that at idle my V8 wasn't needing very much fuel. No thaving had access to a W/B way back then didn't heklp things either - I can only imagine what A/F was 8O

[Lowell Foo]

I've had no problem idling 1000cc injectors on Supras or DSMs using the boost comp table and a low microsec/bit value.

[Kenneth Steinbach]

I have no clue what brand of injectors are in my Supra, only that they flow 720cc. Is this important or should I just leave it as is? I never realized this was any big deal. I did notice that my AFR would change at idle depending electrical load/voltage so I fiddled with the battery offset table until AFR was consistent. Did I screw up?

[fastlyf]

HELLO I HAVE A HONDA CIVIC AND INSTALLING A AEM EMS UNIT I GONNA PUT IN 1000 CC INJECTORS THAT ARE LOW IMPEDENCE I WANTED TO KNOW IF I STILL HAD TO USE A RESISTOR BOX WITH THE AEM  THANKS JAMES

[9krpm]

which is a better or ideal injector type for 1000cc for a 4 cylinders engine?

[Sherman Daley]

A couple years ago I was told by a tech at RC Engineering that no one made an injector larger than 440cc in hi impedance for the 2J Toyo rail configuration. If this holds true for your application then your question might be moot - in other words, the 1Kcc injector might be only available in low imp.

Sherm...

[9591]

Using the EMS, it won't matter which type is used. The EMS has saturated-type drivers, so even if peak-and-hold injectors are used (with resistors, of course), they will still operate as saturated.

[9krpm]

I am getting a set of 1kcc Rochester inj
I got the impression that they are high impedance though.....will wait and see.  I wonder if AEM has got a map for these badboys

[AnArKey]

Good point, a low impedance injector run through a resistor, will be operating as a saturated injector. You need a special peak and hold driver circuit, AND a low impedance injector, to get the advantages of peak and hold.

One other advantage of P&H over saturated, is the ability to work at higher pressures. The extra umph of the initial current is able to open the injector against higher pressures than a saturated injector, as well as being faster and more responsive.

[9krpm]

I just got these injectors.
The place I got them in NSW does know much about them at all

Thanks to Google
You are right Sherman Daley
these injectors are low impedance types
Rochester 8281 1710498 1008cc (96)

SA, could you please confirm that the battery offset for Rochester 1008cc work for these injectors?

[JS]

One other advantage of P&H over saturated, is the ability to work at higher pressures. The extra umph of the initial current is able to open the injector against higher pressures than a saturated injector, as well as being faster and more responsive.

This statement is not entirely true. The basic style of injector (i.e. pintel, disc, ball, etc...) makes more of a difference than how the inector is controlled. I can run a pintel injector at 120psi of pressure no problem on a saturated driver. A disc injector on a peak & hold can start to lockup at 100psi or more.

Jason.

[B951S]

Who sells resistor packs for using P&H low impedance injectors?

[BLKMGK]

Who sells resistor packs for using P&H low impedance injectors?

Digikey sells resistors, RadioShack might have them, some Hondas have them, MKIV Supras have them... Nothing special here other than perhaps power handling capability - they can get pretty hot! How many injectors you need to cover?