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TPS/Fuel Pump/A/C Clutch Fan electrical gremlin

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Old 12-15-2019 | 02:56 PM
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gearhad's Avatar
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Model: Cherokee (XJ)
Default TPS/Fuel Pump/A/C Clutch Fan electrical gremlin

I've encountered and defeated many gremlins in my jeeps circuitry, but this one is by far the strangest and I don't even know where to start.
1997 XJ Sport 4.0 Standard Transmission.

First I got a code 24 on my dash for high/low voltage to the TPS, so like a fool I bought a new one on the way home right after seeing the code, seeing as I have 257k and its a routine part, I figured that would be an easy fix, but it didn't clear the code. So I went ahead and measured the voltage of the output on the TPS harness, with the TPS itself unplugged. What should have been no more than .5V has consistently been 4.67V, so its an internal wiring problem. This is where it got weird.

Keep in mind, I drive the standard, so a faulty TPS circuit isn't really effecting the way my car runs. I keep it in neutral at a stop so its not dying, and I'm shifting on my own, so TPS isn't causing weird shifting. Only thing I've noticed is that cruise control isn't working ideally, and it doesn't accelerate as smooth as it did.

TPS Harness Test:
Before I go on, I wanna make it clear that I read about and tested the clockspring, unplugged everything including the horn relay, and still had 4.67 on the TPS harness.
So I hooked up the voltmeter with the key on and started pulling fuses to see if anything was interfering with the TPS circuit, and when I pulled the 15 amp blue fuel pump fuse, the A/C clutch fan kicked on and the TPS output voltage dropped to a normal .45V, figured it would be either the fan or pump interfering, so I just unplugged the fan, took the fuse out again, fan stayed off, voltage dropped, so the fan should be ruled out.

So now I'm really confused because the fuel pump works, I can hear it running, and when I drive (remember the TPS isn't effecting my driving) everything is fine. Pulling the fuel pump relay or any other related fuses doesn't do anything, just the one 15 amp blue fuel pump fuse, and why would that kick on the A/C fan? Im kind of losing my mind.

I can only assume something in the fuel pump circuit interferes with something in the TPS circuit, or the PCM is acting weird. So I'm completely lost, I don't have any wiring diagrams to look at, so I can only hope someone on here has had a similar experience.

Please help I feel about 2 inches tall right now.

Thanks.
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