Help with codes/CEL (Pin 46/30)

[89livelystang]

Alright, i'm going to apologize for the long post first. I have been searching and searching trying to find what's going on and these forums are a lifesaver so thanks in advance!!

The issue that i'm having is that I have Signal Return when clutch pedal depressed but as soon as i release the clutch it goes away....below are my troubleshooting factors.

I have an 89 5.0 manual vert. The check engine light has been on for a while and i've been doing some investigating to see what the problem is. Did the self-test and got codes 51,22,53,54,35,67. I ruled out that they all had something to do with the Signal Return (Pin 46), so i took the ECM out and checked for a burnt trace. The EEC-IV that i have is a A9M and it looked fine inside. After searching more forums i found out that the 02 sensor harness "jumper" has something to do with it. Since my computer is an A9M (Auto) and i have a manual transmission i figured i would do the swap that everyone was talkign about on the 02 harness. Swapped the jumper from manual to auto and i now have Signal Return from all Sensors, however this is only with the clutch pedal depressed. Has anyone heard of this???

As soon as i let the clutch pedal out the signal return goes away. I ran the self-test again after getting the Signal Return taken care of and i received codes 22,and 67, with the clutch pedal depressed. Upon further investigation last night i noticed that the Light Blue/Yellow and Black/White wires that come from the Clutch Switch and go into a connector near the center console under the dash didnt' have anything connected to the other side of it. Is this normal? I searched and searched for the plug that mates to the other side of it and can't find it. Please help!!!

 

[junkyardwarrior]

Does it have the manual trans harness? The auto harness and manual trans harness are different, and to add insult to injury, the 90-93 2.3 manual trans harness is different than the pre '90. With any trans harness other than the V8 T5 harness, you will get a code 67 with the clutch pedal released. Some guys like to jumper pin 46 to ground but thats kind of a rigged way of doing it. Suggest finding the proper trans harness (and I have one left over from another project).

The connector under the middle of the dash I am not familiar with. Perhaps someone with more knowledge of that part of the harness will know for sure.

 

[Mustang5L5]

So this is a 5-spd swap car?

Do you know how the trans harness was connected to the t-5? Was it done with the factory harness connected to the reverse lights?

With a 5-spd swap, you do not need to change out harnesses or computers. So with AOD computer, you can still use your o2 harness and trans body harness. The only changes to wiring needed are to plug in the factory t-5 reverse harness, and plug the clutch switch wires into the clutch safety switch. Everything should work fine then.

Was this car a 4-banger as well?

 

[89livelystang]

Junkyardwarrior

It does have the manual trans harness i believe but i have read on these forums that you can just change the jumper wire in the harness and that will convert it. Before i swapped the jumper wire on the harness i wasn't getting a signal return ground for the sensors (TPS, BARO, ACT). Now that i have the jumper swapped i have sig return but only with the clutch pedal down. I ripped apart the dash last night to try and find anything out of the ordinary. I'll definately post on what i find.

Mustang5L5

I don't believe that is was a 4-bangor, i'll have to run the VIN to find out. The car has had like 8 previous owners. As far as the T-5 harness goes i'll have to do some investigating to find out. I know for sure that the plugs on the back of the clutch switch are plugged in with the Red/Blue that go to the starter solenoid and the blue/yellow and black/white that are supposed to come from Pin 30 at the ECM, but like i said in the first post there is a connector that has a blue/yellow wire and 2 black/white wires running into it with nothing connected to the other side. If i could find out what's supposed to go there i think the problem would go away.

 

[jrichker]

The engine running codes will only run with the clutch dedal depresssed. Are you saying that you have to depress the clutch pedal to get .5-2.0 ohms between the singnal ground on the TPS/MAP/EGR/ACT/ECT and battery ground? When The signal ground circuit is working correctly you will get the .5-2.0ohms at all times,

Signal ground troubleshooting 91-93 5. ) Mustangs

The computer pin 46 signal ground is a critical component: it provides ground for the TPS, ECT, EGR position sensor and ACT. Signal ground is used in many circuits that have analog inputs to isolate the electrical noise. It is always separate from power ground, although both may have a common connection origination point. Signal ground usually has some conditioning that reduces the electrical noise to prevent false readings
The gray/red wire (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. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. What sometimes happens is that the test connector gray/red wire 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.

See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.


If the ground for the TPS goes bad, the TPS output voltage increases and the idle speed goes up.



Troubleshooting signal ground problems:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
1.) With the power off, measure the resistance between the computer test ground
(Gray/red wire) on the self test connector and battery ground. You should see less than
2.0 ohms.

2.) MAP circuit: Check the resistance between the gray/red wire on the MAP/BARO sensor and then the gray/red wire on the EGR and the same wire on the TPS. It should be less than 1 ohms. Higher resistance than 1 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire. Next check the resistance between the gray/red wire and the negative battery cable. It should be less than 2.0 ohms.

3.) Engine mounted sensor circuit: Check the resistance between the gray/red wire on the TPS and battery ground. It should be less than 2.0 ohms. Higher resistance than 2.0 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire.

 

[89livelystang]

The engine running codes will only run with the clutch dedal depresssed. Are you saying that you have to depress the clutch pedal to get .5-2.0 ohms between the singnal ground on the TPS/MAP/EGR/ACT/ECT and battery ground? When The signal ground circuit is working correctly you will get the .5-2.0ohms at all times,

Sorry i forgot to specify that when i ran the self-test it was KOEO. When i press the clutch down i can start the test because then i have signal return but as soon as let off the clutch the test ends because signal return is no longer there. Also when i start the car with the clutch pedal depressed everything works as advertised but as soon as i let out the clutch (while it's in neutral) the idle goes up to like 2000 rpm and it runs like crap! Oh, and the car is an 89 so the signal return wire is black/white

 

[89livelystang]

Alright so here's what i found. I checked all the wiring and that was good so i figured i would check the computer and see if i had continuity from pin 46 to pin 40. I got nothing....needless to say when i opened the computer the other day to check for the burnt trace i neglected to take the circuit board out and check the other side. It is definately gone!! So now i'm kind torn between trying to re-solder the connection (i can't solder that well), splice into the black/white sig return wire and ground it, or just buy another computer. ANy inputs???

 

[jrichker]

Alright so here's what i found. I checked all the wiring and that was good so i figured i would check the computer and see if i had continuity from pin 46 to pin 40. I got nothing....needless to say when i opened the computer the other day to check for the burnt trace i neglected to take the circuit board out and check the other side. It is definately gone!! So now i'm kind torn between trying to re-solder the connection (i can't solder that well), splice into the black/white sig return wire and ground it, or just buy another computer. ANy inputs???

Find someplace or someone that repairs TV's or radios. They can fix the burned trace in about 10 minutes if you have the circuit board in hand.

Be aware that the circuit board is sensitive to static electricity and is easily damaged even by small static electrical discharges that you won't notice or feel. Wrap the circuit board in aluminum foil since it is doubtful that you have one of the anti-static bags available.

 

[89livelystang]

Find someplace or someone that repairs TV's or radios. They can fix the burned trace in about 10 minutes if you have the circuit board in hand.

Be aware that the circuit board is sensitive to static electricity and is easily damaged even by small static electrical discharges that you won't notice or feel. Wrap the circuit board in aluminum foil since it is doubtful that you have one of the anti-static bags available.

Unfortunately i'm over here in the UK and places like that are few and far between, so i decided to do it myself. After careful consideration the job is done and i verified that i now have continuity from pin 46 to 40 and 60 on the EEC-IV. Thank you all for the support getting me through this. When i ran the KOEO test last night Code 67 is no longer there. I still have a few codes that i need to fix 22 (BARO) and 87 (Fuel Pump Relay Wiring), but other than that it's fixed. THanks again!!

 

[jrichker]

MAP/BARO sensor operation and code 22

Revised 19-Jul-2011 to add functional descriptions for MAP and BARO operation.

On a Speed Density car, the MAP/BARO sensor is connected to the intake manifold and acts to sense the manifold pressure. Lower vacuum inside the intake manifold when combined with more throttle opening measured by the TPS means more airflow through the engine. As airflow increases, fuel flow through the injectors needs to increase to keep the air/fuel ratio where it needs to be. When manifold vacuum increases, the engine is either decelerating or idling, and it needs to reduce the fuel flow through the injectors.

On a Mass Air car, the MAP/BARO sensor vents to open air and actually acts to sense the barometric pressure due to changes in weather and altitude. Its purpose is to set a baseline for the computer to know the barometric pressure. As barometric pressure decreases, it leans out the fuel flow to compensate for less oxygen in the air. When the barometric pressure rises, it increases to add fuel since there is more oxygen in the air. The fuel requirements decrease as altitude increases, since the atmospheric pressure decreases.

Disconnecting the MAP or BARO sensor will set code 22.

Misconnecting the BARO sensor to vacuum on a Mass Air car will cause the computer to lean out the fuel mixture.

Code 22 or 126 MAP (vacuum) or BARO signal out of range. The MAP or BARO sensor is pretty much the same sensor for both Mass Air & Speed Density cars. The main difference is where it is connected. Mass Air cars vent it to the atmosphere, while Speed Density cars connect it to the intake manifold vacuum. Its purpose is to help set a baseline for the air/fuel mixture by sensing changes in barometric pressure. The MAP or BAP sensor puts out a 5 volt square wave that changes frequency with variations in atmospheric pressure. The base is 154 HZ at 29.92" of mercury - dry sunny day at sea level, about 68-72 degrees. You need an oscilloscope or frequency meter to measure it. There a very few DVM’s with a price tag under $40 that will measure frequency, but there are some out there.

The MAP/BARO sensor is mounted on the firewall behind the upper manifold on 86-93 Mustangs.

Baro or MAP test using frequency meter - run the test key on engine off. The noise from the ignition system will likely upset the frequency meter. I used a 10 x oscilloscope probe connected from the frequency meter to the MAP/BAP to reduce the jitter in the meter's readout.

If it is defective, your air/fuel ratio will be off and the car’s performance & emissions will suffer

Some basic checks you can make to be sure that the sensor is getting power & ground:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm.

The following power on check requires you to turn the ignition switch to the Run position.
Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.



Code 87 – fuel pump primary circuit failure. The fuel pump lost power while the engine was running. Check fuel pump relay, check inertia switch, wiring to/from inertia switch, red wire going to inertia switch for +12volts. Check the other side of inertia switch for +12 volts.

Diagram of the fuel pump wiring for 86-90 cars

Diagram of the fuel pump wiring for 91-93 cars.