Electronic feedback control systems may be a necessary requirement for conversion certification in your locality. If you do a lot of driving, you may want to do this upgrade to just improve your LPG fuel consumption. Since the fuel mixture is controlled by the shape of the gas valve in the mixer, there is no real way to adjust it as you would a gasoline carburetor. There is an idle mixture control and a power mixture control. The power mixture control has a minimal effect at cruising speeds and affects the full throttle power fuel mixture by restricting the flow of propane entering the mixer.
Electronic control systems typically measure the exhaust oxygen (O2) content and control the fuel mixture by adjusting the output of the propane converter's pressure regulator. These systems are called closed loop systems because the controller continually measures the exhaust O2 and adjusts the fuel mixture. Open loop systems are like old-style carburetors in that the carburetor solely controls the fuel mixture and there is no fuel mixture readjustment as the engine is running. Open loop propane converters produce a low (measured in inches of water) but constant output pressure.
Tom Jennings upgraded his 1963 Rambler to a closed loop system and noticed an immediate improvement in his fuel consumption and drivability. He used the Autotronics 4046 Close-Loop Controller and found that their instruction manual left out a lot of small but important details. If you are considering trying this system, read the Tom Jennings experience first.
We have a closed-loop fuel mixture controller (similar in operation to the Impco ADP and Commander). An addition feature it has (that the ADP, Commander, and Dual Curve PN5952 do not) is the integral status indicator lamps:
- 4 amber LED lamps for constant monitoring of the fuel system
- Red/Green/Amber exhaust oxygen indicator lamp
- Check Engine lamp (with remote indication)
These lamps allow the installer to easily setup the fuel system as well as it provides an “at a glance” view of the current engine condition. Clogged air filters and fuel system problems are easily diagnosed using these indicators. If the controller is unable to maintain the correct air/fuel ratio due to a fuel system fault there is a “Check Engine” lamp that will illuminate to advise the operator that there is a potential emission problem.