TPS Improver
Scott Moody - smoody@redstone.army.mil
Introduction
Here is a low-cost way to improve your TPS voltage signal. This scheme allows you to set your idle TPS setting to a normal value ( .35 - .45 volts) and have a high WOT value (4.6 - 4.9 volts). With this setup, I have my TPS set at .36 volts at idle and it provides over 4.8 volts at WOT. This is accomplished with a resistor (R), a microswitch (limit switch, SW), a mounting bracket, and some small hardware for SW mounting. The schematic diagram below shows the electrical hookup. The parts are available at Radio Shack for a total cost of approx. $4.50. The connector naming convention is for '86-'87. This may or may not increase your performance
Circuit Diagram
Circuit Operation
The circuit operation is pretty simple. The TPS is basically a potentiometer with the TPS signal (Vtps) to the computer following the potentiometer rule. The signal will vary somewhere between the supply (A, 5.0 volts) and analog ground (C, 0.0 volts), depending on throttle opening. When the throttle is near WOT, the switch (SW, roller type) will operate and will include the resistor (R, 1000 ohms) in the circuit, increasing Vtps. The steady-state voltage (B, Vtps) can then be easily determined using elementary circuit analysis techniques.

Electrical connections to the TPS can be made with another pair of the Packard weather-pack connectors (from GM, or Molex .093 terminals) or you can disassemble the harness-side TPS connector and make solder connections to the back of the terminals there. Solder one end of the resistor (might need some wire) to TPS connector A, the other end of the resistor to the "NO" switch contact. Connect (via a wire) the "C" switch contact to TPS connector B. Make sure everything is insulated.

Since there are variations in TPS's, you might want to try different values for the resistor; lower resistor value gives higher voltage. Try 820 or 1200 ohms to suit. It's probably a good idea not to go above 4.9 volts. Optionally, a .1uF capacitor (Copt) can be placed between the ground terminal C and the signal terminal B to slow the electrical operation of the circuit. Also, this capacitor will help worn TPS's by suppressing electrical noise (scratchiness) at all throttle positions.


A mounting bracket will have to be fabricated for the switch. Start with a cardboard template and then use tin snips to cut an aluminum plate to match. I put the bracket under the TPS held by the two TPS mounting screws. The mounting holes in the bracket for the microswitch should have some tolerance to allow for switch adjustment. The TPS lever should contact the switch's arm (or roller) near WOT. I have mine set up to operate the switch at approx. 4.0 volts. Be careful to not over-bend the switch lever. The idle TPS voltage is set up as per the shop manual. Check operation with a voltmeter. Check for binding or interference !!!

Ideally, a sealed (weatherproof) microswitch should be used but you can buy 10 regular switches for the price of a sealed unit, and they're easy to replace. Just use connectors instead of soldering to the switch's terminals.


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