With all the recent discussion of Delphi injectors

[E Vader]

-Low Impedance injectors -

This seemed like a good contribution to the braintrust.

What is the difference between low-impedance and high-impedance injectors?

"The important difference between low- and high-impedance injectors is the amount of electric current they require. The high-impedance injectors used by carmakers do not use much current. In fact, even if you connect one directly to your car's battery, it will not draw much juice. This is good for the car maker because the circuit in the ECU that runs the injectors can be a simple switch made from cheap, light-duty components.

A low-impedance injector needs a bunch more electric current to open, about 4 times as much as the high-impedance injector. This is so much current that the injector will burn itself out unless the juice is somehow turned down right after the injector opens. Now, instead of a simple, cheap on/off switch, the ECU must use heavy-duty components that can handle 4 times as much current. The switch must also turn down the flow of electricity after the injector opens so the injector doesn't burn up. This is a much more expensive circuit, and one that generates a bunch more heat inside the computer. Getting rid of that heat raises the computer cost even more.

This business of the ECU yanking the injector open with full current, then turning down the juice to keep it open, is why you hear low impedance injectors called "peak and hold". It takes a big current (the peak) to yank them open, but a much smaller current (the hold) to keep them open.

So why bother with low-impedance injectors if they're harder to run? Because bigger electric currents can yank harder than smaller ones. As the flow rating of an injector increases, so does the weight of whatever the injector uses to turn the fuel on and off (for example, a pintle, or a disk). This is no big deal for stock injectors in the 18 lb/hr to the 30 lb/hr range. Even though they are high-impedance, they're light enough that the small current can yank them open quickly.

But big (like 42 lb/hr and up) high impedance injectors are slow to open. This makes it hard to get a good idle, and kills throttle response. What if you need an injector larger than 42 lb/hr? Simple! You buy low-impedance injectors, which are available up to 160 lb/hr. The large peak current can quickly snap these monster injectors open.

So a low-impedance 50 lb/hr injector will almost certainly be "snappier" than a high-impedance 50 lb/hr injector. When the 50 lb/hr high-impedance injectors on the Acceleronics test car were replaced with 75 lb/hr low-impedance injectors, the ECU setting that adjusts for "sluggishness" had to be set back to stock. The high-impedance 50 lb/hr injectors required much more time to open than stockers, but the low-impedance 75 lb/hr injectors are just as snappy as stockers."

How do I tune my engine for low-impedance injectors?

"Your ECU doesn't care whether the injectors are low-impedance, or high-impedance. It only cares about how big they are, and how quickly they open. You will need to change the number that tells your computer how big the new injectors are. For example, when the Acceleronics Camaro changed from 50 lb/hr high-impedance injectors to 75 lb/hr low impedance injectors, we used LT1-Edit to change the "injector size" from 50 to 75. Nothing to it!

If you removed larger-than-stock high-impedance injectors, your new injectors will probably open more quickly, so you may need another adjustment. Again using the LT1-Edit example, we changed the values in the "injector offset versus voltage" table. Your ECU may call it something else, but there is probably a similar offset number that tells the computer how snappy, or how sluggish, the injectors are. Once the injector size and injector offset numbers are fixed, continue tuning as usual."

Written by Jeff Stevens. Copyright © 2002-2004 Acceleronics.com All rights reserved. Revised: October 24, 2004 .

[Mike2kS4]

But they're too small. I'm going to test some High Impedance Siemens/Deka injectors soon.

[Funkweasel]

[-SlowSilverTIPJason-]

tunercat .tdf file for it, but he's not giving it up so easily. He also has a prog. to calculate the edited values checksum and rewrite over the k-line. We really need a good way into this ECU. That would end all our BS ways out of ECU problems like boost deviation and MAF sizes.

[Mike2kS4]

Using RS4 MAF electronics to even everything out.

[Funkweasel]

the angle spray pattern as well? Did you get the specs(spray angle, lowest ms, etc)?

[Mike2kS4]

I got the fine cone pattern. They seem damned responsive at low pulsewidth: Gain= 0.11ms/mg, Offset: 0.055ms, Turn on time: 1.14ms.

[Funkweasel]

[Captain Matt, I be]

changes.

From the info i've seen though, the program is prohibitively expensive and is far from user friendly. I know theres a few on this board with access to it, perhaps they'll see fit to comment.

[Mike2kS4]