so i don’t need to worry about the transmission sensor as long as the clutch pedal one is hooked up?
An NGS not hooked up could cause a high/hanging idle.
My car doesn’t have it hooked to the trans but it’s hooked on the clutch pedal. If I slow down and slip the trans out of gear wen not under load, the idle will hang until I press the clutch pedal in
Clutch pedal and trans NGS are wires in parallel
@jrichkerYou used the wrong ground to check the TPS voltage...
Why do the engine control sensors have a separate ground?
The computer pin 46 signal ground is a critical component: it provides a signal ground for the Map/Baro, TPS, ECT, EGR position and ACT sensors. Every sensor has to have a reliable ground for it to provide accurate and useful information to the engine control computer.
The more current that flows through a conductor, whether it is a cable or the car body, the greater the voltage drop. The ground on the car body and ground cable for the engine block may have different voltage drops. Some of the voltage drops change depending on electrical loads such as lights, A/C, and heater blower settings.
Under high current loads, there can be large changes in the voltage drop across the ground wiring that goes back to the negative battery cable. If the engine analog sensors ground is combined with power ground, the computer will see these changes in the ground as a change in sensor input. This voltage change is very undesirable for reliable computer operation, so the engine sensors all have a separate shared ground.
The engine mounted sensors all have outputs of 5 volts or less. Therefore, any small changes in voltage seen by the computer analog signal inputs can have a large effect in engine performance. Signal ground is used in many circuits that have analog inputs to eliminate the voltage drop across the engine block and body grounds when current flows through them. There is very little current flowing through the signal ground and the voltage drop across the signal ground is so small that it can be ignored by the computer.
The voltage output of any sensor must always use the signal ground for the sensor under test in order to eliminate any errors or variances. That way, what the voltmeter sees is what the computer sees unless there is a problem with the sensor wiring.
@Blown88GT
@Mustang5L5
@a91what
You guys have anything to add or modify here?
Thanks @General karthief !See #10 of the checklist
@jrichker
so I’ll check the voltage again, besides the computer is there anywhere specific that particular ground runs to so i can check? Just trying to figure out how difficult that might be as one person is all
Each engine mounted sensor has the black/white signal ground wire as part of its connector wiring.
There is a black/white wire on the TPS plug that is the signal ground.
The following are diagrams courtesy of Tmoss & Stang&2birds
Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.
TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif
Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs
Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs
5.0 wiring diagram for Fuel Injectors, Sensors, and Actuators
Ignition switch wiring
O2 sensor wiring harness
Vacuum diagram 89-93 Mustangs
HVAC vacuum diagram
TFI module differences & pin out
Fuse box layout
Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif
87-92 power window wiring
93 power window wiring
T5 Cutaway showing T5 internal parts
Visual comparison of the Ford Fuel Injectors, picture by TMoss:
Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif
Engine mounted fuel injector harness
Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
Starter circuit
Alternator diagram for 94-95 Mustangs.
I tried getting a reading using the Black ground on the tps connector and the green wire, but was not getting a reading. I’m going to check again tonight and see if I get a reading straight from the harness connector pins And then reconnect the tps and check again to make sure I don’t have a broken ground wire
so i don’t need to worry about the transmission sensor as long as the clutch pedal one is hooked up?
Well, ideally you should have both hooked up. Otherwise it gets old sitting at a stoplight with the clutch in so your idle doesn't hang. With the NGS on the trans hooked up, when the stick is in neutral you can let the clutch out and it will still idle low like it should
[If you don't own a Multimeter or DVM or don't know how to properly use the one you have, you will need some one on one help from someone who knows how to correctly use your meter.
Troubleshooting loss of signal ground on pin 46 for 86-90 model 5.0 Mustangs.
Revised Sep-22-2019 to add back probing the connections to test the TPS voltages
A fault in the TPS circuit where the voltage goes above. 4.3 volts at idle can shut off the injectors.
TPS adjustment:
You need to do the testing with the TPS sensor plugged in as it would normally be when the engine is running. Use some safety pins to probe the connector from the back side to make contact with the wires,
Wire colors & functions:
Orange/white = 5 volt VREF from the computer
Dark Green/lt green = TPS output to computer
Black/white = Signal ground from computer
Always use the Dark green/lt green & Black/white wires to set the TPS base voltage; anywhere from.5 to 1.0 volt is OK
Do the test with the ignition switch in the Run position without the engine running.
Use the Orange/white & Black white wires to verify the TPS has the correct 5 volts source from the computer.
Adjusting the TPS fails to resolve the problem:
If the adjustment does not work to get the voltage below 1 volt, you probably have a bad signal ground. The black/white wire is computer pin 46 and is signal ground for many things. If it burns up inside the computer you get multiple faults and cannot pull codes.
Disconnect the positive battery cable to insure correct results when measuring the resistance of grounds. The small voltage drop that is often in a circuit can cause erroneous readings. Since the computer and several other things still draw current even with the ignition switch in the Off position, this is a necessary step.
Check the black/white wire resistance. Connect one ohmmeter lead to the black/white wire on the TPS and one lead to the negative post on the battery. You should see less than 1.5 Ω; more than that indicates a problem. Always take resistance measurements with the circuit powered off.
Check the resistance of the black/white signal ground on the MAP/BARO sensor on the firewall behind the upper intake manifold. The resistance should be less than 1.5 Ω If the resistance value of the black/white signal ground on the MAP/BARO is1.5 Ω and the TPS is higher or doesn't read at all, then there is a problem in the engine mounted fuel injection harness or the 10 pin connector
Clean the 10 pin salt & pepper shaker connectors.
Diagram courtesy of Tmoss & Stang&2birds
See the graphic for the 10 pin connector circuit layout.
The injector power pin is the VPWR pin in the black 10 pin connector. [/b]
How it is supposed to work:
The black/white wire (computer pin 46) is signal ground for the computer. It provides a dedicated ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self test mode. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1.5 Ω when measured from anyplace on the engine harness with the battery pigtail ground as the other reference point for the ohmmeter probe. What sometimes happens is that it gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60, which are power ground for the computer.
See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix for the computer internal signal ground.
How to test the wiring:
Disconnect the positive battery cable to insure correct results when measuring the resistance of grounds. The small voltage drop that often in a circuit can cause erroneous readings. Since the computer and several other things still draw current even with the ignition switch in the Off position, this is a necessary step.
With the power off, measure the resistance between the computer test ground (black/white wire) on the self test connector and battery ground. You should see less than 1.5 Ω
If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the black/white wire and pin 46: it should be less than 1.5 ohms. More that 1.5 ohms is a wiring problem. If it reads 1.5 ohms or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1.5 ohms. More that that and the computer’s internal ground has failed, and the computer needs to be replaced.
Measure the resistance between the black/white wire on each of the following sensors: TPS, ECT, ACT and EGR. If you find one that is greater than 1.5 Ω, measure between that sensor and pin #1 of the white 10 pin connectors. Pin #1 is the center pin and is labeled sig-rtrn on the diagram
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.
Ignition switch wiring
Fuel, alternator, A/C and ignition wiring
Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
Vacuum diagram 89-93 Mustangs
HVAC vacuum diagram
TFI module differences & pinout
Fuse box layout
Glad to hear.
Should be further evidence when guys go on a "You don't need that...delete it" spree and then wonder why their car doesn't run well
Going to try and get a better picture tomorrow in the daylight. I haven’t been able to find that mount that is attached to the car so far, but it looks like maybe some spot welds broke?still running great and could not be happier!
now to figure how to fix my driver side fender that somehow got messed up. Not sure if I should start a new post or not. Looks like the tab attached the body of the car got partially pulled off where it attaches to the rear fender by the door. Any suggestions?
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