7727 & Low Impedance Injectors

[Scott68B]

I did do a search but didn't get a definitive answer so pardon the question if it has already been answered.

I'll be doing an engine swap at some point in the not too distant future and I'm thinking about keeping my 7727 in place at least initially. The motor I'm swapping to has low impedance injectors. Is there, in fact, a modification/workaround that would allow the 7727 to drive those injectors?

Thanks in advance for your help.

Scott

[dave w]

I found the information (Formulas) below from a MegaSquirt website.

Injector Resistors
This method has been used by many OEMs as a simple approach to driving low-z injectors. The installer has the option of installing a 5 to 8 ohm resistor (with a 20 to 25 watt rating) in series with each injector (in effect converting them to hi-z.)
1980s Volvos were fitted with a resistor pack that conveniently combines a number of resistors.
To limit the current to under 2 amps, you need:
resistor ohms = (alternator voltage / 2.0 amps) - injector resistance
For example:
resistor ohms = (14.0 volts / 2.0 amps) - 1.2 ohms
=> resistor ohms = 7.0 - 1.2 = 5.8 ohms

dave w

[RobertISaar]

depends on how low of impedance and how many of them.

[1project2many]

Right. With enough injectors you'll need to exchange the injector driver for one which can handle more current. Or you'll have to use an external driver box.

[Scott68B]

Thanks for the response everyone. There will be 8 of them and they're on a 2006 5.3 LS motor. I will have to test them. If needed, does anyone know the part no. for the injector driver?

Thanks again!

Scott

[1project2many]

The number I used several years ago is no longer available and I'm not sure what's being used these days. I believe the SyTy guys do injector driver upgrades fairly often so you might want to look around at code59.org. I've posted links to a web page before with upgrade instructions for a 7749. The 7730 is similar but only one driver. I *think* Bill Shaw was the man who posted the howto that I linked to.

[dave w]

Thanks for the response everyone. There will be 8 of them and they're on a 2006 5.3 LS motor. I will have to test them. If needed, does anyone know the part no. for the injector driver?

Thanks again!

Scott

Don't forget the Injectors (Impedance) for the 1227727 ECM are in Parallel. http://www.1728.org/resistrs.htm

So one bank of four (high impedance) injectors, that individually measure 16 ohms each would = 4 ohms of resistance to the injector driver. If one bank of four (low impedance) injectors, that individually measure 1.6 ohms each would = 0.4 ohms of resistance to the injector driver. So I'm thinking with my example of four low impedance injectors measuring 1.6 ohms in parallel, the inline resistor of 3.6 ohms (25 Watts) is needed for the 1227727 injector driver.

There is the option of using two stock injector drivers soldered in parallel to divide the current path. Big heat sinks are good things to have on injector drivers!

dave w

[Scott68B]

Sorry for the delay in responding. I finally got out to the garage and tested my injectors. They averaged about 11.5 ohms. So does that mean they're high or low....as far as the 7727 is concerned?

Thank you

Scott

[dave w]

Sorry for the delay in responding. I finally got out to the garage and tested my injectors. They averaged about 11.5 ohms. So does that mean they're high or low....as far as the 7727 is concerned?

Thank you

Scott

11.5 ohms is usually considered high impedance, but works out to something like 2.875 ohms, which is on the edge of being safe for the '7727 injector driver. I think if I was going to try what your wanting to do, I would use a 1.2 ohm resistor in series with the four parallel injectors just to be safe.

I've done something similar to what you want to do with a Vortec 454 I converted to a '7730 ECM. The Vortec 454 injectors measured close the 14 ohms, so I did not use a resistor.

dave w

[Scott68B]

Thank you for the information! It's a big help.

Regards

Scott