Mustang TPS Adjustment - 0.99v not necessary

jrichker · Oct 3, 2015

@92Vert50

Troubleshooting low or missing 5 volt Vref

All tests done with the ignition switch in the Run position but the engine is not running.

The orange/white wire supplies 5 volts reference (Vref) for the TPS, MAP/Baro and EGR sensors.

Engine Mounted sensors

The TPS and EGR get their 5 volt Vref through the engine mounted fuel injector harness & the 10 pin connectors.

See the graphic for the 10 pin connector circuit layout.

A bad connection or broken wire in the engine mounted fuel injection harness is not uncommon. Check the EGR sensor orange/white wire for good 5 volt Vref. If it is good there, the TPS has either a broken wire or bad connection.
Good 5 volt Vref at the ERG sensor, then you have a 10 pin salt & pepper connecter problem or a computer problem.

Check for 5 volt Vref on the orange/white wire at the firewall mounted MAP/Baro sensor. Good 5 volt Vref there, then the problem is in the 10 pin salt & pepper connectors or in the engine mounted fuel injection harness.

No 5 volt Vref at the MAP/Baro sensor, then the problem is either a broken wire in the main fuel injector harness or the computer has died.

Remove the passenger side kick panel to gain access to the computer.

Locate the orange/white wire (pin 26) on the computer connector and check for 5 volt Vref. Good 5 volt Vref and the computer is OK.

Diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

Mustang5L5 · May 31, 2018

What a great thread. Had to reference it tonight

akaNYr · Apr 21, 2019

Mustang5L5 said:
Added more tech data. Hopefully any tps questions can be directed here

This is a an old post but I'm going to throw this out here anyway. SN95's don't have an adjustable TPS. Drilling the holes does nothing to adjust volts. I tried it and the TPS didn't move. SN95 TPS Volts are adjusted by the screw under the rubber cap on top of the throttle body. I think it's called the idle air bypass screw. It takes an Allen key to adjust It. It took many days of aggravation and research to find this out. There should be separate forums titled 'SN95 tech info' and 'Fox body tech info'.

BlakeusMaximus · Apr 21, 2019

There are separate ones. Fox 5.0 tech and 94-95 specific tech.

jrichker · Apr 22, 2019

akaNYr said:
This is a an old post but I'm going to throw this out here anyway. SN95's don't have an adjustable TPS. Drilling the holes does nothing to adjust volts. I tried it and the TPS didn't move. SN95 TPS Volts are adjusted by the screw under the rubber cap on top of the throttle body. I think it's called the idle air bypass screw. It takes an Allen key to adjust It. It took many days of aggravation and research to find this out. There should be separate forums titled 'SN95 tech info' and 'Fox body tech info'.

None of the Mustangs had an adjustable TPS.

You missed the point entirely, which is that attempting to adjust the TPS is totally infective for increasing performance.
When the computer powers up, it takes whatever reading the TPS puts out as the zero or starting point to look for increases beyond that value. If you set it at 0.99, the computer thinks that is the zero point and looks for increases beyond that value.

akaNYr · Apr 22, 2019

jrichker said:
None of the Mustangs had an adjustable TPS.

You missed the point entirely, which is that attempting to adjust the TPS is totally infective for increasing performance.
When the computer powers up, it takes whatever reading the TPS puts out as the zero or starting point to look for increases beyond that value. If you set it at 0.99, the computer thinks that is the zero point and looks for increases beyond that value.

I'm not trying to increase performance, I'm trying to stop my car from suddenly surging to 2,500 or 3,000 RPM'S.

RaggedGT · Apr 22, 2019

akaNYr said:
I'm not trying to increase performance, I'm trying to stop my car from suddenly surging to 2,500 or 3,000 RPM'S.

That info is in this thread(I’ll link towards the bottom) listed under Base idle reset- I actually used this thread yesterday to cure a similar issue on my ‘94 .
https://www.stangnet.com/mustang-forums/threads/help-me-create-the-surging-idle-checklist.698148/

Mustang5L5 · Apr 22, 2019

akaNYr said:
There should be separate forums titled 'SN95 tech info' and 'Fox body tech info'.

There are. This post is in the "FOX 5.0 Tech" Forum. There is a separate forum for 94-95 5.0's.

https://www.stangnet.com/mustang-forums/forums/1994-1995-specific-tech.66/

Noobz347 · Apr 22, 2019

General karthief · Apr 22, 2019

Those guys should have wrenches in their hands and stangnet stickers on the uniforms.

Noobz347 · Apr 22, 2019

General karthief said:
Those guys should have wrenches in their hands and stangnet stickers on the uniforms.

I'll fix that as I have the time.

Sure would be nice to have a "scouter" where I could just look at a car and pull all the ECU codes.

93gtmustang · Apr 11, 2021

Checked my TPS. Key on was .75 WOT 4.58
That's within the proper range right?
Does it matter if the car is cold or hot?
Is it necessary to check it at idle?

Mustang5L5 · Apr 11, 2021

No, not necessary to check with car running. Throttle blade position at idle and with car off is the same. Battery voltage might be a tad bit higher though, so actually value might be higher.

you can double check by running your codes and seeing if any tps codes pop up

93gtmustang · Apr 11, 2021

Mustang5L5 said:
No, not necessary to check with car running. Throttle blade position at idle and with car off is the same. Battery voltage might be a tad bit higher though, so actually value might be higher.

you can double check by running your codes and seeing if any tps codes pop up

Thanks!

Trogdor · Apr 13, 2021

Where did the. 99 volt myth come from?

General karthief · Apr 13, 2021

From Chrysler, they told CNN and we know what happens after that.

Mustang5L5 · Apr 13, 2021

Trogdor said:
Where did the. 99 volt myth come from?

I believe it was in a Mustang magazine or early website back in the day. Part of the 5-minute tuneup.

It's essentially non-adjustable, but the myth still persists.

It can still be faulty, which causes issues in how the car runs, but setting it to an arbitrary number is meaningless which you take into account what the ECU is doing with this number.

Dan02gt · Apr 13, 2021

Trogdor said:
Where did the. 99 volt myth come from?

My guess is that the logic behind the myth is that the ideal voltage for the TPS is 5v at WOT so setting the TPS at .99V with the TB (the max they thought was acceptable) ensures the WOT TPS voltage is at high as possible to ensure the ECM's WOT strategy is used. Now we know there is a range that's acceptable for both and as long as you are in that range it makes no difference in performance.

7991LXnSHO · Apr 13, 2021

Trogdor said:
Where did the. 99 volt myth come from?

I remember MM& FF or Hot Rod magazine doing a Ten Minute Tune Up, (maybe it was 5), and a track test. They were trying all the low or no buck tricks they heard about trying to get the cars faster & quicker when they were much newer and parts were still being developed. I which I had saved that article for fun.

Mindseye007 · Nov 2, 2022

Mustang5L5 said:
EDIT: This post applies to 86-93 5.0 Mustangs.

Seems to be a common myth, so lets sticky a thread explaining how the TPS works. Jrichker has provided the basic TPS guideline to follow. I'll just preference it with this.

Adjusting your TPS to .99999999 volts is not necessary at all. There is a general range the computer will accept as idle voltage for the TPS. This range is 0.5 - 1.25 volts. ANYTHING within this range is acceptable.

If idle voltage is outside this range, a TPS code is generated by the computer.

Therefore, the only adjustment really necessary is to verify the tps voltage at idle is anywhere between the above range. If this is a FORD OEM tps, it should be. Aftermarket TPS's might be different and require you to slot the holes to get it in range. If it is in range, then you are fine. No need to chase the mythical 0.99 volts that has been tossed around for years. Upon vehicle startup, the computer will take the base idle voltage, and apply a certain voltage value to that number as the trigger point for WOT operations. I've seen 2.71-3.13 throw around as the value increase over baseline idle voltage as triggering WOT. The value is adjustable and can be changed by tuning

To make a long story short. If your idle TPS voltage is anywhere between 0.5V and 1.25V...you are good to go.

Mine is set at 0.99 and has some superballs with that setting. She Just takes off like a jet lol along with my 4.10 gears .

Mustang TPS Adjustment - 0.99v not necessary

jrichker

StangNet's favorite TOOL

Mustang5L5

That is…until I whipped out my Bissell

akaNYr

BlakeusMaximus

Still got to try a little lube on my speedo head

jrichker

StangNet's favorite TOOL

akaNYr

RaggedGT

Been here over a DECADE and still no CT

Mustang5L5

That is…until I whipped out my Bissell

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

General karthief

wonder how much it would cost to ship you a pair

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

93gtmustang

Mustang5L5

That is…until I whipped out my Bissell

93gtmustang

Trogdor

General karthief

wonder how much it would cost to ship you a pair

Mustang5L5

That is…until I whipped out my Bissell

Dan02gt

mazing how much gas smell came from that tiny hole

7991LXnSHO

wanna catch the space herp

Mindseye007

10 years still blowing strong

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