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Resolved Question

Tps feed wire has constant 5 volts

by Dec 27, 2016 5:52PM PST

Help please, totally stumped. My 95 xj 4.0 sport manual had a bad missfire on acceleration so i decided to change the tps. No change. I tested the wires on tps plug coming from ecu and the middle feed wire had a constant flow of 4.83 volts. So i decided to test the feed wire coming out to tps from ecu and it has 4.83 volts. Im confused, isnt the feed wire supposed to receive and not send voltage ???

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Bobs95xj has chosen the best answer to their question. View answer
5 Posts
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Best Answer

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that ain't how it works
by Dec 28, 2016 4:11PM PST

hi it's not quite clear what you're actually looking at. the wire from the ecu to the tps is supposed to have close to 5 volts on it. the tps is just a potentiometer. both wires are supposed to read approximately 4.8V if you're measuring it out of circuit.
that is to say, if you unplug the return wire and measure you will see 4.8V on both wires regardless of the position of the throttle.
you gotta leave both wires connected with the engine running and find a way to measure the V on both of them. one should be a constant 4.8 and the other should range up and down while you turn the throttle.

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Explanation
by Bobs95xj Dec 29, 2016 5:02AM PST

With ignition on the ON position and tps unpluged im getting 4.8 going to the feed wire from the ecu. Isnt the feed wire only supposed to send fluctuating power when i turn the throttle?

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Explanation
by mikewax Dec 29, 2016 9:24PM PST

i'm not following what you're saying. Here's a picture to clarify things.
http://i252.photobucket.com/albums/hh18/Lytnbug/Bonneville/TPS-CTS-IATckt.gif
the top wire (416) should be 4.8V as long as the engine's running. the middle wire (417) should range from 0V at idle to 4.8V at WOT. the bottom (452) will be 0V.
if your TPS has a similar setup then you need to tap the middle wire somehow and measure the voltage between it and ground while you goose the throttle.
of course, you gotta find out which wire is which. you may have to measure all three.

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Fixed !!!
by Bobs95xj Dec 30, 2016 9:56AM PST

Thanks for help. Problem fixed. Over looked the obvious. Bad Tps.

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Fixed !!!
by mikewax Dec 30, 2016 10:44AM PST

thumbs up Happy

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