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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What did I say in 2013? It's been a while so some things might have changed.

I'm not as good with SN95 cars as I am with fox electrical as it's been some time since I've owned my 2003. The Fox cars do not require a specific set voltage point and can accept a pretty wide range. Based on what i've seen from the A9L, it's 0.5-1.25V. The internet quotes a lot of different numbers but that's taken directly from the A9x programming that someone shared with me years ago. Anything at idle is acceptable and the ECU will just take that as a reference voltage so it knows when WOT is achieved.

Sn95 cars are the same way, but I do not know the acceptable range. It's not an absolute number, but a range.

Also, do not test the signal wire to vehicle ground. You want to test that to sensor ground. So really Gray/Red to the Gray/white and see what voltage you get there. Going to battery ground may give you a different reading
Your were chiming in with Jrichker helping a fellow member @89blufox, your statement was regarding 5v on power wire. Taking what both of you said, I have been trying to dial in my situation. I can't seem yet to figure out why my signal wire is sending such low voltage through the range.

I am led to believe its either a bad 'standard' sensor or I have my signal wire grounding somewhere in the harness.

In my case, I did exactly that, signal wire and signal ground with KOEO.

TPS - 93' 5.0 'Standard' brand on my 2003 ECU GT
Signal Wire (red probe) / White/Grey Ground Wire (black probe)
Closed: -0.252v
WOT: -1.600v maximum

Question: Why negative values & Why is it soo low?
I think your gray/red is the signal ground, but that's going off your providing wiring diagram. I think the 5Vref is the brown/white wire.

Brown/white (red probe) to Gray/red (black probe) = ?
Gray/white (red probe) to Gray/Red (black probe) = ?


I think read that wiring diagram same as the above. Gray/red is your sensor ground. Black probe there.

So try

Brown/white (red probe) to Gray/red (black probe) = ? (should be 5V)
Gray/white (red probe) to Gray/Red (black probe) = ?

Here's the fox sensor wiring for reference just to verify you've hooked the right colors to the SN95 wiring harness. Like i stated before, the desired set voltages are all over the place on the internet.

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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.

@Mustang5L5, your last post to me regarding the wiring harness for both the 93' TPS and the 99-04' TPS made me go back and double check prior work which I assumed was good and figuring it we've made it this far in the swap and addition of parts. So kudos to you brotha.

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

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