| TPS Adjustment |
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TPS adjustment is not an absolute input to the EEC. The EEC WILL compensate for any TPS adjustments you make. The Throttle Position Sensor (TPS) is a rotary potentiometer that provides a voltage signal to the Powertrain Control Module(PCM) that is linearly proportional to the throttle plate/shaft angular position. The TP sensor is mounted on the throttle body and is non-adjustable. As the TP sensor is rotated by the throttle shaft, four (4)operating conditions are determined by the PCM from the TP sensor.
The four (4) vehicle operating conditions are:
? Closed throttle (idle or deceleration)
? Part throttle (cruise, moderate acceleration)
? Wide open throttle (maximum acceleration, de-choke on crank and A/C shut-off)
? Throttle angle rate.
A key difference between EEC-IV, OBD I and EEC-V, OBD II is the monitors. EEC-IV monitors are designed to identify system and component issues. EEC-V monitors are designed to measure the ability of systems and components to maintain low emission levels.
Set TPS to 0.98 volts, set initial timing to 14 degrees.
Remove the TPS from the throttlebody, using a thin file (or drill) increase the size of 1 mounting hole slightly. Remount the sensor but do no tighten all the way. Use a voltmeter and probe the ground and signal wire which if I remember correctly is black and orange with gray stripe. With the TB closed and the key "ON" engine off, slightly slide the TPS around until you reach 0.98(or close to it) and tighten down completely, check again its very sensitive.
Well, before you set the TPS, here's some stuff to thisnk about.
First, the TPS sensor is not adjustable and if you want to try, you have to hog out the mounting holes of the sensor in order to get it to turn.
Second, The ECM goes to full-throttle fuel strategy when the voltage from the TPS reaches about 4.5 volts (before the throttle plate is fully open), so adjusting the TPS voltage higher doesn't get you anythisng at WOT.
Third, the ECM is programmed to compensate for any differences in sensors (like say when you replace a faulty one), and automatically re-adjusts to a common base voltage when the throttle is closed.
And finally, even if you achieve a slightly rich mixture at part-throttle settings, the oxygen sensors will detect this and re-program the fuel curves. You end up right back where you started.
By the way, even if you could modify it for slightly more fuel, running a rich mixture is bad. Over an extended period the extra fuel could cause wear of the rings and cylinder walls, higher tailpipe emissions, and much higher catalytic converter temperatures.
If the TPS voltage 'didn't' go high enough at WOT, then you wouldn't enter "full throttle strategy". If you don't enter "full throttle strategy", then your A/C doesn't cut out, your EGR valve stays open, the cooling fan doesn't cut out, etc., so if your A/C and cooling fan DOES cut out when you tromp it, you HAVE reached "full throttle strategy" mode. Any further increase in TPS voltage does nothing.
Oxygen sensors can indeed detect rich mixtures. Sensor output is about 600 mV at the classic 14.7:1 fuel ratio and will rise to 800 mV at just 2/10th's of one point richer (14.5:1). It is a feedback system whereby the the fuel ratio is constantly adjusted. If I may quote Charles Probst; "Closed-loop air-fuel ratio control operation is known as 'short-term' trim. It must operate quickly and continuously to maintain air-fuel ratios as close as possible to the stoichiometric" (14.7:1). Any attempt to alter the fuel ratio will be immediately compensated for by the ECM ('short-term' trim). In a short period of time (after a pre-determined number of samples) the ECM will write the new requirements into the fuel maps. If you seriously altered the mixture richer so that the ECM can no longer compensate, it will set a trouble code and turn on the "check engine" light.
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