Installing the Throttle Position Sensor (TPS)
NOTE: Failure to follow this instructions can result in permanent damage to the TPS unit. Be certain that when first installed, the throttle travel does not exceed the range of motion for the sensor. If the sensor is rotated beyond it’s range, it will be internally damaged and must be replaced. Warranty does not cover broken sensors.
Prior to installing the Throttle Position Sensor (TPS) there are a few critical points that need to be understood and addressed to avoid damaging the sensor and to achieve optimum performance. Please read through all of these next few pages to fully understand what needs to be done with regard to throttle rotation, TPS installation and adjusting the TPS.
Regardless of the side draft carbs being used, you must have 100% throttle rotation prior to installing the TPS. In the example below we’re using the Zenith Stromberg 175CD carbs but the same idea applies to any of the carbs used. If you’re unsure how to accomplish this, please consult your car’s manual. In the example below the carbs are obviously off of the car, so I’d recommend that you first check by pushing down on the throttle linkage between the carbs and check the rotation on all of the carbs. If you’re not getting 100% rotation you first need to adjust your carb linkage per your car’s manual. Once you have 100% rotation by pushing down on the linkage I’d suggest you have someone sit in the car and hold the accelerator pedal to the floor while you observe the amount of rotation at the carbs. If you no longer have 100% rotation you now need to adjust the accelerator control rod.
Here you can see the throttle arm at rest against the idle stop screw.
With full rotation, the arm has moved 100% and rests in this position. If you do not have full rotation, you will need to adjust your carb linkage or accelerator control rod per your maintenance manual. Failure to do this result in TPS installation problems.
You should now have 100% rotation using both the carb linkage and the accelerator pedal so it’s time to install the TPS bracket, driver nut and sensor.
NOTE: On later model TR6’s with smog pumps, an AIR tube passes down to the exhaust manifold close to the left side of the rear carb where the TPS needs to be mounted. If your car is still so equipped there may be clearance issues. One solution has been to gently bend the tube rearward as shown here. Be careful as those tubes are often very fragile and replacements are hard to find.
As you can see, the back of the sensor has two notches that engage the driver nut. DO NOT over rotate the internal mechanism of the sensor.
This is the driver nut the goes on the end of the throttle shaft and is locked in place by the set screw in the middle of the nut. DO NOT over tighten the nut onto the throttle shaft. If you strip the throttle shaft threads you’ll need to replace the shaft. Just finger tighten the driver nut on to the shaft and maybe give it a very very small turn with a wrench. You need to be able to rotate the driver nut back and forth to set various parameters for the sensor. The set screw is what locks it into position.
You can see how the notches on the sensor engage the notches on the driver nut.v
A self-explanatory picture of how it all fits together.
The original nut holding throttle linkage onto the end end of the throttle shaft can be removed with a 7/16″ or 12MM wrench. Turn counter clockwise to remove it. Remove the nut and the star washer behind it. Usually there are two thick slotted washers-so remove one of them.
Shown here is the new TPS driver installed. Finger tighten the driver nut plus a very small turn with a wrench. The set screw is what locks the nut in place. DO NOT over tighten the driver as it will strip the threads on the throttle shaft and that can only be repaired by replacing the shaft! If there are two thick slotted washers on the throttle shaft. One of those two should be removed and replaced with a wave washer. Place a wave washer from the kit onto the shaft and thread on the driver in place of the original nut. As a starting point, the driver should be positioned with the slot aligned in the 10 / 4 o’clock position. Inside the driver is an Allen head set screw that is tightened to lock the driver in place and allow adjustment. You will need a 1/8″ Allen wrench.
The bracket mounts to the carb mounting studs, one underneath the carb and one above. Removing the nuts will require a 1/2″ open end wrench. With these nuts and washers removed, the bracket can be installed. Start with the driver thru the hole in the bracket then lay the bracket over the studs. Put the nuts and washers on finger tight. The arrow shows a round file to illustrate the driver slot angle relative to the bracket with the throttle linkage at FULL throttle. It should be vertical at full throttle at this initial setting and will be further adjusted later as the readings will be too low.
This is what the stainless steel bracket will look like once installed. Notice the angle of the driver’s slot at idle. The top bracket tab goes under the nut holding the carburetor to the intake manifold
Position the bracket so that the driver is centered in the bracket opening & then tighten the mounting bolts. You can test the alignment by slipping the TPS sensor onto the shaft and rotating it counter clock-wise. If the sensor’s locating ring slides into the bracket without binding, the alignment is correct. If the alignment is still off you may need to loosen the bracket mounting nuts and reposition or even slightly bend the bracket with a pair of pliers. The driver is locked in place by tightening the internal Allen screw.
The TPS unit needs to be pre-loaded during installation. In other words, when you mate the TPS to the driver nut, the TPS will be off center as shown in this somewhat exaggerated picture. You then turn the TPS counter clock-wise to get it to drop in to the bracket. Proper preloading of the TPS is CRITICAL as it determines the voltage readings sent to the ECM.
Install the sensor using the two screws supplied. You will likely need to wiggle the sensor or move the throttle shaft to engage the sensor’s tabs. Be sure the tabs are engaged properly before tightening the mounting screws. Using your hand, be sure that the throttle moves freely over it’s range without binding or sticking. That’s it.