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TPS Sensor 94 3.3L - info

1849 Views 1 Reply 2 Participants Last post by  Bob Lincoln
FYI...things the manuals don’t tell you:​

The Holley TPS sensor on my 1994 Grand Caravan with 3.3L engine is essentially a potentiometer with a resistance range of about 250 to 2000 ohms (signal pin 2 to gnd pin 1). It goes open circuit at the top end - the throttle does not use the full range of the potentiometer, with throttle closed it is at least twice the 250 ohms, I did not check the top end.​

Low resistance (low voltage when connected) is at low throttle opening, high is at high.​

You have to fiddle a bit to ensure the engagement bar on the throttle shaft is on the correct side of the mating projections in the TPS (a cylindrical well with two triangles projecting into it), so that you get rotation of the sensor. To be sure I hooked meter leads to the pins with the TPS off, put the TPS in position, and confirmed rotation was occurring by watching the meter both before and after installing attachment screws.​

We can expect wear of a potentiometer in positions it spends most of its time at, due small movements. My high-mileage one has fluctuations on a digital ohmeter when I tap it with throttle sitting closed. I don’t know how significant that is, I’ll probably replace it for good measure.​

BTW, after you lose a screw, you may want to know that the thread is 10-32, shank 1 1/8”, pan head. Screwdriver is Torx T25. If substituting with standard screw note that the Chrysler screw has blue locking compound on the threads so you need to use similar or a lockwasher.​

(Removing the TPS is awkward because there is limited clearance to the brake master cylinder. Fortunately I had a hex-to-¼” square drive adapter so could use a ¼” ratchet. Magnetism is desirable as holding the screw while taking it out of the area is somewhat awkward, I’m going to put a strip magnet in my special bit set and ¼” ratchet set, as some adapters are only weakly magnetized. And find my grabber tool.)​

[I know, the bolts attaching many things in the area are metric, but the screws attaching the IACM and TPS are standard US Imperial. Both TB and TPS are made by Holley.]​
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Your explanation of the pot is lacking some detail. The signal voltage is about 0.7V with throttle closed, and about 3.7V to 4.0V with throttle wide open. So while the resistance measurement from signal to ground varies from about 200 ohms with throttle closed and (you measured) 2000 ohms with throttle wide open, if you measure from signal to supply voltage (which is about .4.8 to 4.9V), you get the opposite - about 2000 ohms at throttle closed and about 2000 ohms at wide open throttle.

Also, different sensors have different resistances. On my Dakota truck and on my Daytonas, the total resistance range is 200 ohms to 5,000 ohms.
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