Electrical constant 4.59 volts

matteo323

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Jan 3, 2019
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Hey guys this is my first post need help. My car is a 93 lx 5.0 5speed car.This car was converted from a 4clyl to 8 cyl. From what I was told it was always a 5sd. problem I'm having is 4.59 volts on green wire of tps sensor. I tried 2 sensors both with same results. I cant pull any codes and have never seeen a check engine light even when the key is first turned on.Where should I start
 
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mikestang63

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if its a conversion who knows how the wiring was hacked... sounds like a bad ground from the black TPS wire through the salt and pepper shaker to the battery ground. The TPS ground runs through the S&P connector pin 5 . These are prone to come loose after time They are located on the back of the upper intake..

1557191658822.png



what voltage do you get from the orange wire....does the voltage vary when you open the throttle when testing the green or orange wire... You should ground out to the black wire on the TPS not anywhere else. Also did you install the TPS with the bottom on the slot the right way it needs to be able to sweep from under t to over 4.25 as the Throttle opens.

It SHOULD be with key on

orange - 5 volts FROM EEC
green- .8-1.1 volts TO EEC with throttle closed and smooth increase to over 4.25 V as you go to WOT. anythiing from .8 to 1 is fine
black- ground to computer
 
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matteo323

Member
Jan 3, 2019
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Wayne ,New Jersey
Hi and thanks for the info. The harness doesn't look to be all taped up and spliced together, The orange wire is giving me around 5v last time I checked. Voltage on the green wire does increase to 4.88 when I sweep throttle. I have checked voltage with tps mounted and just with it plugged in , just to see if I installed it incorrectly and have also tried another tps with same results. I will start with the info that you have provided and see what happens. Thanks again
 

jrichker

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Signal ground troubleshooting 91-93 5 Mustangs

The computer pin 46 signal ground is a critical component: it provides ground for the Baro, 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.

583778.gif


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.

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



Fuel injector wiring harness sensors for a 5.0 mustang
63347.gif
 

jrichker

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ok I just checked the resistance on the grey/red wire and battery ground and it's almost 6.0 ohms
Short the meter test lead tips together; you should see less than 1Ω. If you don't the meter is set on the wrong scale, or the batteries are bad, or your meter leads are bad.

If that is true, you have a bad connection somewhere. Repeat the test using the gray/red wire on the MAP/BARO sensor on the firewall; you should see less that 1.5Ω If you you see more than that, you may have burnt signal ground trace inside the computer. See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.
 

matteo323

Member
Jan 3, 2019
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Wayne ,New Jersey
Short the meter test lead tips together; you should see less than 1Ω. If you don't the meter is set on the wrong scale, or the batteries are bad, or your meter leads are bad.

If that is true, you have a bad connection somewhere. Repeat the test using the gray/red wire on the MAP/BARO sensor on the firewall; you should see less that 1.5Ω If you you see more than that, you may have burnt signal ground trace inside the computer. See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.
just touched the leads of my meter together the meter reads 0.00 ohms
 

jrichker

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I took apart me ecu and found the burnt ground trace on the board.The link that jrichker posted doesnt work any other lonks for that ecu repair ?
Thankyou for the heads up, I will do some checking to find a link for the computer repar that will work.