318 MAX fuel economy builds?
Last night when I posted, I was dileriously tired -- I taught a Fuel Efficiency Class this weekend. When I recommended turning the choke spring back, it was because something was improved that justified that action. If you have a stock vehicle, the stock tune is about as good as it's going to get (just ask any Federal judge). Accelerating the warm-up ramp will cause a stumble or even stall, and more importantly from a legal standpoint, higher emissions. Changes to factory settings should be used to compensate for other changes. With that said, if you have a more powerful ignition (Pulstar Plugs, Peaking Caps, PDI, etc) or fuel heater not tied to engine coolant or intake air heater for example, then accelerating the warm-up ramp-in would be justified.
The coolant temp sensor (CTS) is a variable resistor -- like a radio volume knob of yore -- where a change of temperature changes the knob setting. There are charts online that show what the resistance should be at different temperatures for most popular engines. Every CTS I've seen has high resistance when cold, and low resistance when hot. Therefore, if you want to show a hotter temperature, you would have to add resistance in parallel to the sensor, reducing overall resistance. To show colder temperatures, add resistance in series in either of the 2 wires. I use the resistance value at 68 degrees F. for the base value.
A quick internet search suggests a value of 2k - 3k ohms at 68 for a '98 Magnum engine. Usually the resistance ranges on both the CTS and IAT sensors are pretty close. So, if you wanted to show colder air, you would add resistance in series. Using the 2500 ohm average resistance value, we want a potentiometer with a value slightly higher than that. Cheap pots will be 2.2k, 2.7k, 3.3k, 3.9k, or 4.7k ohms in that range. I'd go for the 4.7k ohms for a bit more range. Cut one of the sensor wires and splice the pot center tap to one of the wires, and either of the 2 outer taps to the other end of the cut. Watch your Scan Tool and turn the knob slowly to see which direction increases the effect. Higher resistance will show cooler temps.
To show hotter air or engine temp, you need to splice a pot in parallel. However, here you want a value around 10X the base value. Remember, the rating of the pot is its MAX value. Turning the knob will reduce resistance where eventually it acts as a short. For this reason, you would want the pot rated at least at 10X the base PLUS a current limiting resistor rated about base value. Let's put this together: 2.7k limiting resistor (1/4 watt 20% tolerance is just fine) and a 27k pot (again, low wattage value OK). The 2.7k resistor is soldered to one of the outer legs on one end, and one of the 2 sensor wires on the other end. The center tap of the pot is soldered to the other sensor wire. Here, lower resistance will show hotter temps.
Last night when I posted, I was dileriously tired -- I taught a Fuel Efficiency Class this weekend. When I recommended turning the choke spring back, it was because something was improved that justified that action. If you have a stock vehicle, the stock tune is about as good as it's going to get (just ask any Federal judge). Accelerating the warm-up ramp will cause a stumble or even stall, and more importantly from a legal standpoint, higher emissions. Changes to factory settings should be used to compensate for other changes. With that said, if you have a more powerful ignition (Pulstar Plugs, Peaking Caps, PDI, etc) or fuel heater not tied to engine coolant or intake air heater for example, then accelerating the warm-up ramp-in would be justified.
The coolant temp sensor (CTS) is a variable resistor -- like a radio volume knob of yore -- where a change of temperature changes the knob setting. There are charts online that show what the resistance should be at different temperatures for most popular engines. Every CTS I've seen has high resistance when cold, and low resistance when hot. Therefore, if you want to show a hotter temperature, you would have to add resistance in parallel to the sensor, reducing overall resistance. To show colder temperatures, add resistance in series in either of the 2 wires. I use the resistance value at 68 degrees F. for the base value.
A quick internet search suggests a value of 2k - 3k ohms at 68 for a '98 Magnum engine. Usually the resistance ranges on both the CTS and IAT sensors are pretty close. So, if you wanted to show colder air, you would add resistance in series. Using the 2500 ohm average resistance value, we want a potentiometer with a value slightly higher than that. Cheap pots will be 2.2k, 2.7k, 3.3k, 3.9k, or 4.7k ohms in that range. I'd go for the 4.7k ohms for a bit more range. Cut one of the sensor wires and splice the pot center tap to one of the wires, and either of the 2 outer taps to the other end of the cut. Watch your Scan Tool and turn the knob slowly to see which direction increases the effect. Higher resistance will show cooler temps.
To show hotter air or engine temp, you need to splice a pot in parallel. However, here you want a value around 10X the base value. Remember, the rating of the pot is its MAX value. Turning the knob will reduce resistance where eventually it acts as a short. For this reason, you would want the pot rated at least at 10X the base PLUS a current limiting resistor rated about base value. Let's put this together: 2.7k limiting resistor (1/4 watt 20% tolerance is just fine) and a 27k pot (again, low wattage value OK). The 2.7k resistor is soldered to one of the outer legs on one end, and one of the 2 sensor wires on the other end. The center tap of the pot is soldered to the other sensor wire. Here, lower resistance will show hotter temps.
