TPS voltage (not what you're thinking)

[Neltech]

So I picked up a new TPS thinking that it was the problem but this one does the same thing. With the key on i'm getting 5v at all 3 wires using the motor as a ground. I check the voltage between the black and orange and its minimal like 0.0x volts.

You guys ever ran into this?

 

[Bills89GT]

I don't know what the the problem is that you are having or whats done to your car. But I had the same readings at the tps sensor when my ecu was bad. Turned out I had the wrong O2 harness when i did my v8 swap and burnt a trace on 2 new ecu's before i figured it out. I was unable to pull codes so that's what tipped me off

here is the thread...
http://www.stangnet.com/mustang-forums/825204-did-i-fry-my-ecu.html

 

[Neltech]

Lots of good info in there thanks. I know there is an o2 plug that goes to nothing. There is a relay on the passenger fender with a wire where was just charred, then 3 broken wires on some emission pump. I can pull codes, and lots of them. It's an 87 with a 89 maf conversion backyard install

 

[kpack5982]

the voltage you need to check between is the green wire and the black one.

 

[jrichker]

See the "Adjusting your TPS to .99 voltis isn't necessary" sticky at the top of the forum for help troubleshooting TPS problems.

 

[Neltech]

I did check that voltage,same as black to Orange

 

[RangerJoe]

I agree with Bills89GT. I had a similar problem. You shouldn't have voltage on your ground. A swapped O2 harness or a short between two wires will provide power to the ground and will burn out your pin 46 ground in the ECU. If this is the case, FIX the issue first. I burned a friends ECU up too trying to trouble shoot the problem before realizing what was happening.

Follow the link above to trouble shoot, but if that doesn't work, disconnect battery, remove ECU, plug battery back up and use a DVM to check pin 46 at the ECU harness. Check with key on and with key in crank position. After fixing mine it would still read a very negligable voltage (like .006 volts), but before I was getting like 4 or 5 volts I think.

Good luck, let us know what you find.

 

[Neltech]

Awesome thanks. Ok I know what an O2 sensor is and the plug but can someone describe what a swapped o2 harness is and why someone would swap it?

 

[Mustang5L5]

Using an o2 harness that doesn't match the transmission

Do you have an o2 sensor harness at all? The plug is on the pass side, and then it splits down below and connects tp the two sensors

 

[Bills89GT]

You mentioned something about some shorted wires on some other plugs, that may have something to do with the problem, the ground that goes to pin 46 on the ecu also goes to several other sensors. It goes to the tps sensor (obviously), EGR position sensor, coolant temp, air charge temp, BAP, the self test connector, and a couple other switches/sensors, try checking the wire to ground in a few other sensors and see if you have the same thing there. If you don't have one i'd grab a haynes manual and trace the wires out. it was very helpful for me

There is a thread somewhere around here that has pictures of several different configurations of the O2 harness. if nothing was changed on yours it shouldn't be an issue but but if there is any chance it has been changed you may want to look into it because Ford had different harnesses for different years and for different trannies.

 

[Neltech]

I think it was an auto but now its a 5 speed

 

[Bills89GT]

was the ecu swapped or left for the auto? you also said it was swapped to mass air, what ecu was used for that? if the ecu put in for the mass air was matched to the manual tranny rather than an auto and the o2 harness is for an auto you may have burnt something up

 

[jrichker]

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 black/white 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 black/white
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.
Only an experienced electronics technician can open the computer up & repair the trace if it burns
up and creates an open circuit.

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. That means disconnecting either the battery positive or negative cable since there is always some current draw due to the computer and radio circuits.

1.) 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 2.0 ohms.

2.) MAP circuit: 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 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 black/white wire.
Next check the resistance between the black/white wire and the negative battery cable.
It should be less than 2.0 ohms.

3.) Engine mounted sensor circuit: Check the resistance between the black/white 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 black/white wire.
Repeat the process for the ACT and ECT sensors. Your results should have the same specifications.

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

 

[Neltech]

After a few hours of digging through wires with my meter and taking my computer apart twice I fixed it. Found my passenger side o2 wasn't plugged in, random wires frayed, fixed those, fixed the burned out trace on the computer. She fired right up, drove it around a bit and parked it for 10 minutes and it fired right back up. I didn't check if it threw any codes, that's tomorrow. Thanks a bunch all of you! The only thing is that it still chugs while trying to hold speed.