How to tell the difference between an LH-2.4 and LH-3.1
#1
05-29-2013, 10:46 PM
How to tell the difference between an LH-2.4 and LH-3.1
I have done some research and figured out the easiest way to tell if you have one of those rare LH-3.1 fuel injection systems. Just look at the mounting holes on the Idle-switch / throttle-position-sensor.
Super-Quick Summary:
The LH-2.4 idle switch has oblong mounting holes for adjusting its position. The LH-3.1 throttle position sensor has round holes that fit the screw perfectly because it does not need to be adjusted.
Detailed Description for Newbies:
The throttle body is the cast aluminum-alloy thing connected between the intake manifold and the air-intake ducts. On the back side of the throttle-body (towards the rear of the car) is a large switch in a black, plastic housing. This is either the idle-switch or the throttle-position-sensor, depending on which model of fuel injection system you have.
For the LH-2.4 this is actually two switches in a single housing. It only detects when the throttle is at idle and at full-throttle. It needs to be adjusted so the switches get actuated at the precise correct throttle-valve angle. So the mounting holes are oblong. You can see the "excess" hole sticking out from under the mounting screw heads. This switch is also shaped like a rectangle with two corners cut off at a 45 degree angle. Plus the mounting flanges and socket for the electrical connector.
For the LH-3.1 this is really a potentiometer. It detects every position of the throttle-valve. It does not need to be adjusted because the ECU just detects the minimum and maximum voltage coming through the potentiometer and assumes that is the closed and open position of the valve (this is from my Bentley manual). This is why it is called the "Throttle Position Sensor" and there is no need for adjustable slots. (Some people use the two terms "Idle Switch" and "Throttle Position Sensor" interchangeably, but they are two different devices.) This gizmo is shaped more like a rectangle with two corners just slightly more rounded than the others. Plus the mounting flanges and socket for the electrical connector.
I know there are not a lot of LH-3.1 systems out there. But the VIN for my car indicated that it may have either the 2.4 or the 3.1 with no other indication as to which I really had. So, I didn't know exactly what troubleshooting steps I should take in certain situations. Now, hopefully you won't be stuck in that conundrum.
Super-Quick Summary:
The LH-2.4 idle switch has oblong mounting holes for adjusting its position. The LH-3.1 throttle position sensor has round holes that fit the screw perfectly because it does not need to be adjusted.
Detailed Description for Newbies:
The throttle body is the cast aluminum-alloy thing connected between the intake manifold and the air-intake ducts. On the back side of the throttle-body (towards the rear of the car) is a large switch in a black, plastic housing. This is either the idle-switch or the throttle-position-sensor, depending on which model of fuel injection system you have.
For the LH-2.4 this is actually two switches in a single housing. It only detects when the throttle is at idle and at full-throttle. It needs to be adjusted so the switches get actuated at the precise correct throttle-valve angle. So the mounting holes are oblong. You can see the "excess" hole sticking out from under the mounting screw heads. This switch is also shaped like a rectangle with two corners cut off at a 45 degree angle. Plus the mounting flanges and socket for the electrical connector.
For the LH-3.1 this is really a potentiometer. It detects every position of the throttle-valve. It does not need to be adjusted because the ECU just detects the minimum and maximum voltage coming through the potentiometer and assumes that is the closed and open position of the valve (this is from my Bentley manual). This is why it is called the "Throttle Position Sensor" and there is no need for adjustable slots. (Some people use the two terms "Idle Switch" and "Throttle Position Sensor" interchangeably, but they are two different devices.) This gizmo is shaped more like a rectangle with two corners just slightly more rounded than the others. Plus the mounting flanges and socket for the electrical connector.
I know there are not a lot of LH-3.1 systems out there. But the VIN for my car indicated that it may have either the 2.4 or the 3.1 with no other indication as to which I really had. So, I didn't know exactly what troubleshooting steps I should take in certain situations. Now, hopefully you won't be stuck in that conundrum.
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