I dont understand what these terms mean. Far as i know it has something to do with the ecu?? Can someone help me out??

 

Open loop and closed loop is a term used in control systems. Our cars have a control system to keep the fuel mixture at 14.7:1 under normal conditions. Closed loop is when your ECU is using the signal from your O2 sensor as it’s “feed back” to control your fuel mixture. For example, if the car is running lean it injects more fuel to bring the mixture back up. Thus, in closed loop mode it will continually monitors your car’s A/F mixture and make adjustments to the amount of fuel injected many times a second. The slight amount it changes your fuel mixture is stored in your ECU and is called your Short Term Fule Trim (STFT) value. The STFT will change many times a second trying to keep your fuel mixture at a perfect 14.7:1.

When the car goes into open loop it will ignore the reading from the O2 sensor and inject fuel based on default fuel maps and your Long Term Fuel Trim (LTFT) value. The LTFT changes much slower and is used to compensate for a car running a little too rich or lean all the time. Like if your fuel filter is getting a little clogged it might make your LTFT value go up to compensate for this.

Your car is always in closed loop mode EXCEPT when it its not warmed up yet, your at WOT, or your check engine light is on.

I hope that helps out... there is much more depth to this but I didn’t want to get into it too much.

 

That actually helps alot....so since im running off of my 88 fuel pump and filter (that need to be replaced badly) and im running SUPER rich...that would mean im in open loop...thanks for the help