Engine 93 Mustang GT, Code 41/91, KOER Cylinder ID shows 6 and not 8

79MercCapri93

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May 12, 2012
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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

so i don’t need to worry about the transmission sensor as long as the clutch pedal one is hooked up?
 
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79MercCapri93

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May 12, 2012
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You 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?
@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
 

jrichker

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Mar 10, 2000
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lowendmac.com
@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
88-91_5.0_EEC_Wiring_Diagram.gif


Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif


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.
 

79MercCapri93

Member
May 12, 2012
86
7
8
31
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
88-91_5.0_EEC_Wiring_Diagram.gif


Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif


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
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,341
2,679
234
75
Dublin GA
lowendmac.com
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

[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
TPS_IAB_Pic.jpg


See the graphic for the 10 pin connector circuit layout.
68512.jpg

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
 

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
34,702
10,869
224
Massachusetts
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
 

79MercCapri93

Member
May 12, 2012
86
7
8
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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

Cool, well i think ill be ordering the NGS/NSS since it is completely missing. While prior to this I have not had the hanging idle, I think as i have been going through and correcting previous owners works, that I am starting to have issues arise that were not there before as things are starting to work again as they should be.

Out of curiosity, how bad is it to replace the NGS/NSS? From what i can tell, it seems like I might have to drop the transmission to get to it, OR, unbolt the exhaust, and transmission crossmember and slowly drop the backend of the transmission until i can reach without messing up anything up top.

I will also likely try cleaning the VSS today, and see if that makes a difference, and will likely replace that as well given it is original from 93'.
 

Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
34,702
10,869
224
Massachusetts
You have to at least tilt the trans down to get access. All depends on how you work on it. On the ground it's a PITA, but on a lift it's much easier.

There's also a pin that fits under the switch that rides on the shifter rail. Gotta make sure this is there for it to work properly.

That's why mine doesn't work. After getting my t-5 installed after doing the AOD-to-5spd swap...I found the pin on my workbench.
 

79MercCapri93

Member
May 12, 2012
86
7
8
31
[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
TPS_IAB_Pic.jpg


See the graphic for the 10 pin connector circuit layout.
68512.jpg

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

Thanks @jrichker, should have used a safety pin before! Also realized i do need a new negative battery cable. Had to cut and strip the ends due to corrosion from not being sealed terminal ends, but rather the terminal ends that sandwich the cable between the terminal and a plate. But everything checks out, so ill run the car and check for codes and see what i get!
 

79MercCapri93

Member
May 12, 2012
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Looked for codes

KOEO : all good, nothing failed

KOER: 94,44, 33. Which I expected since I do not have my EGR on currently from troubleshooting previously and I don’t not have my smog stuff on.

I am going to try driving the car tomorrow after work and see if any codes come up.

biggest thing I noticed today was the idle fluctuating from 650-1500 rpms after warming up and would go back and forth until the car died. I bumped up the idle screw since I have a e cam, but ran out of time to readjust everything and set the base idle. But if I pressed the clutch in when it first started, the car would start smoothing back out. If it went for to long I would have to tap the gas real quick to get it to level back out
 

79MercCapri93

Member
May 12, 2012
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I am happy to report that the car has been running good. I ended up adding a NGS as the previous owner had ripped it out of the transmission and I had no clue that it was missing. That fixed my idling issues and now I have a steady idle that barely moves fluctuates 25rpms. I also replaced my VSS which fixed my hanging idle issue I was having and now my rpms drop when I come to a stop instead of hanging at ~2000rpms like it was doing. I replaced the NGS about 2 weeks before I replaced the VSS, which worked out good as i was able to differentiate when I saw a difference in the behavior of the car when installing each part seperately, verse installing them both at the same time. Thank you everyone for your help and guidance along the way!
 
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79MercCapri93

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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

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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79MercCapri93

Member
May 12, 2012
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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?
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?