Fuel & Spark For LS Blocks - How It Works

Getting Fuel and Spark to Your Freshly Swapped LS Small-Block is Easier than Ever. Here’s How.

Stephen Kim Nov 17, 2011 0 Comment(s)
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Damon Sampson: From an installation standpoint, Mast Motorsports’ ECMs and wiring harnesses were designed to be as flexible and universal as possible. The harness plugs right into the factory sensors, and all you have to do next is wire up the fuel pump wire, a power wire, and a ground wire and the motor will fire right up. It’s literally a simple three-wire hookup. To simplify things even further, the computer and harness are designed to work as independently from your car as possible. The controls for the cooling fans, A/C compressor, and fuel pump are all part of the computer, not your car. So for guys building a car from the ground up, all you have to do is connect the dots.

Self Learning

Rick Anderson: When you go WOT in an engine controlled by a factory GM computer, it switches to open-loop operation. What that means is that the computer ignores the inputs from the O2 sensors, and adjusts the air/fuel ratio based on pre-programmed fuel maps. On the other hand, Holley’s HP and Dominator EFI systems are fast enough that they stay in closed-loop operation even at WOT. This is what makes the self-learning feature possible. The system continually adjusts the air/fuel mixture based on inputs from the O2 sensors. Let’s say you want the engine to run at a 12.7:1 air/fuel mixture; all you do is punch that target air/fuel ratio into the software, and the wideband O2 sensors compensate for it. After 100 miles or more, you can shut off the self-learning function or trim back the adjustability. The system makes adjustments so fast that it’s hard to believe. For example, we put a 100hp dry nitrous system on a motor with a baseline program, and within one pull on the dyno the air/fuel ratio was corrected perfectly.

Before You Buy

Mark Campbell: Not too long ago, people were able to buy a motor, transmission, computer, and wiring together from a salvage yard, but now it’s becoming harder to do so. Even though a salvage yard might bundle them all together as a complete package, these days it’s not uncommon to get a motor and trans from one car, and a computer from another. The model year of the motor and trans, as well as features, such as variable valve timing, flex fuel capability, and displacement on demand can create compatibility issues between the powertrain and the electronics. GM also used 13-, 15-, and 19-pin harness connectors for transmissions. That’s why it’s very important to get the VIN number of the car that the motor came from. As for the wiring harness, keep in mind that the diagnostic link interface and the check engine light should be included with the harness. Sometimes salvage yards will sell you the main harness without the diagnostic link or CEL. Furthermore, harnesses for manual and automatic transmissions are slightly different. The harness for an automatic can be used on a manual trans car. However, using the harness from a manual trans car on an automatic trans requires hard wiring the harness section from an automatic into the main harness. To simplify matters, Street and Performance can make custom harnesses for any application.

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