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(resolved) 5.4 4v - 03 GT - LOW TPS Voltage

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Bare with me, its a story.

Brothers car. A Frankenstein build

Initially a budget build, but I told my brother, the cheaper you go, the more problems. Taddaaa - here I am in his behalf.

2003 Mustang GT
2003 GT PCM
5.4 4v swapped Navigator engine.
SCT handheld tuner - with GT style tune

Car was running good initially with karkraft intake spacers with 99 Cobra Intake Manifold.

Then more parts came. and so did the problems.

MMR intake spacers
5.0 Coyote Velocity Intake Manifold
1993 year 5.0 style - 90mm Accufab Intake Plenum
Appropriate spacers to make it all work.

Notching the slots for the 99-04 style TPS sensor, I was once able to get it in the KOEO closed throttle 0.90v range but the sensor was not a direct fit to the 1993 Accufab mounting points, so it wouldn't stay within range because of the circular mounting lip elevating sensor from plenum.

Fast forward, we instead opted to get a 1993 style TPS sensor since it would theoretically mate up perfectly. Matched wires from 93 sensor to 99-04 harness and crimped them down for now.

Went online, found forums on TPS over the past 15 years. Nothing matched my scenario, or if it was close, the OP never posted results or ignored the community on advice.

So I took my FLUKE Voltmeter and started at it. Fast learner - here I go.

The issues:
Surging idle, RPM's would rise as the temperature of the car would rise. ~1,100 through ~2,200 rpms.
If I disconnect the IAC, absolutely nothing happens to the idle.
The MAF is an 2001 style MAF; so no integrated IAT.
The IAT is currently missing and plan to add that this weekend. PID's show this sensor at 100 degrees constantly in the SCT handheld scanner.

TPS - 93' 5.0 'Standard' brand

Signal Wire (red probe) / White/Grey Ground Wire (black probe)
Closed: -0.252v
WOT: -1.600v maximum
yes, increases from low value to WOT value at good rate
Question: Why negative values & Why is it soo low?


5v Reference -
Brown/white (red probe) / white/grey (black probe) = 4.779v
Brown/white (red probe) / Accufab Plenum = 5.036v
Brown/white (red probe) / Shock tower ground = 5.040v

without key - engine off
Resistance test
Brown/white (red probe) / negative battery terminal while connected = 2.626
Brown/white (red probe) / negative battery with terminal disconnected = 0.846

This realm of car electronics is new to me, please critique and help me figure this out.

94-04 Haynes Manual

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Disregard this issue everyone; its been resolved. 2 accidentally swapped wires for the TPS at the base harness caused this issue!

Now, we are at:
Closed: 0.83v
incrementally rises to
WOT: 4.650v

Where the 3 TPS wires separate from the harness, (brown/white - grey/white - grey/red), the 2 highlighted in red (red arrows in picture) were swapped thus giving entirely bad readings on every aspect. About 1.5 years ago, the wiring harness for all essential sensors, injectors, etc. received harness extensions per need for a 5.4 4v swapped motor; well human error occured then.

So when I added the new 93' style sensor; while those were crimped to the proper wire intention, the issue was located 3 feet at the other side of the extension near the passenger valve cover.

Anyways. Yep - well here are some photos. Don't mind how dirty she is, its been sitting.


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