SN95 5.0l TPS Voltage WAY TOO HIGH!!! Please help!

[BowTie Eater 5 Liter]

well, i thought my throttle positioning sensor was my problem, so i purchased a brand new one.

what was happening, was the tps was showing 4.79 volts.

i tested all 3 wires
grey wire 4.79ish volts
grey/white wire 4.79 volts also
brown wire 5 volts.

what could the problem be? i replaced the sensor and ive still got the same readings. i can not think of anything else that could be the problem. if someone else could make a suggestion, that would be greatly appreciated.

Thanks, Kris

[tmoss]

If the car runs normally, it is the method your using to measure the voltage. YOPu should be measuring between two of those wires, but I don't know those color codes off the top of my head like the Fox cars.

[Mr 5 0]

On your SN95-model 5.0 TPS, the first grey wire is the ground, the second grey wire (with the white stripe) is the test wire and the brown wire is the 5v source.

So, to test your new TPS you would put the negative lead on your voltmeter to a good engine ground - or the first grey wire. Then you would put the positive voltmeter lead to the middle grey (with white stripe) wire.

You already know that you should be reading around .98-.99 volts and that you should be taking your reading with the engine off, ignition on, right?

Here's a photo to help you out:

http://www.muscularmustangs.com/tps2.jpg

Hope this is of some help to you.

[BowTie Eater 5 Liter]

thanks everyone. measured it properly the first time, unfortunately for me, what could be causing the super high voltage?

yes i tested it key on engine off, thats the first thing everyone suggests, but ive checked tps successfully on many foxbodies, and now this motor. could i have a wire shorting out or something? it just makes no sence to me. could my computer be fried? i hope not because i just replaced this one, but oh well, or could it be a relay or something?

[tmoss]

Sounds like you lost the ground on the return wire from the TPS then - which would make both wires test the same referenced to ground.

[Capri306]

I agree, kind of. I'm willing to be there's either a break in the wiring, causing a short between the +5V rail and the signal return line, or there's an internal problem in the computer (highly unlikely). If BOTH LINES are at the same voltage as you state, try a continuity test between the two to see if they're shorted together, and go from there.

[BowTie Eater 5 Liter]

well i unhooked the tps sensor, and tested the ground wire and the test wire.

with the tps unhooked, the test wire showed 0 volts, the ground however, showed like 3 and a bit volts?

where should i look now?

[mustangII460]

>CLICK HERE<

[Capri306]

Mr. 5.0 and mustangII460, both made excellent posts....but....

WTF is this "TEST WIRE" you keep referring to??? There is no such thing as a "test wire." Do you mean the +5VDC, ground, or signal return??? The black wire should be GROUNDED through the harness, at the computer's chassis, then to vehicle (and battery) ground.

Take some pictures or something; you're confusing the heck outta me, dude.

You should be reading voltage like this:
1. Connect the NEGATIVE lead of the DVOM to the NEGATIVE terminal of the battery.
2. Make sure the DVOM is set to read "Volts," automatic scaling if possible.
3. Turn the ignition switch ON (engine running position but without the engine running).
4. Leave the TPS connected!
5. Using a hat pin, pierce the wire insulation far enough so the pin is almost sticking through the other side of the insulation, one wire at a time; do it on an angle of about 30 degrees from the wire's axis, so you save your fingers.
6. Connect the POSITIVE lead of the DVOM to the hat pin.
7. RECORD the voltage you see on the DVOM.
8. FOR THE LOVE OF GOD, record the color of the wire with the corresponding voltage.

Present your findings here, and I'll be glad to help more.

[tmoss]

Originally Posted by Capri306

.........or signal return??? The black wire should be GROUNDED through the harness, at the computer's chassis, then to vehicle (and battery) ground.

Sig return has more than likely been lost, at the computer or maybe the fender.

[BowTie Eater 5 Liter]

i have done exactily as you explain.
with everything connected, the middle grey/white stripe wire(i refered to it as the test wire because that is the wire you are supposed to test the tps voltage from) shows exactily 4.92 volts.

the top grey(ground) shows 4.92 volts also
the bottom brown wire shows the correct 5 volts.

i did everything else as you have explained

[tmoss]

Some times a graphic can help. If the ground for the computer or the signal return trace on the EEC board is fried, or both, the vref does not have a ground reference in the EEC where it needs to be and the only way to get a vref reading is to use the block as the ground reference.

[Capri306]

If the TPS is connected and he's getting these numbers, I'm agreeing, there's got to be a wiring or other connection problem. A poor or nonexistant ground connection could be the culprit as well, so let's check those ground connections! Make sure there's less than 0.5 ohm between the battery ground and the EEC's chassis, and even then be sure the connection is sound.

Whether it's an internal (EEC) or external (wiring) problem, it's going to be some good ol' harness diving and tracing.....not fun, but necessary. Since you mentioned it happened all of a sudden, I'm thinking that you have a pinched wire somewhere, as happens in so many transplants.

I just don't see how you're getting almost 5V on the TP's signal line (going back to the EEC) if the TPS is connected and there aren't any shorts in the system....usually this happens if the TPS is shorted internally. If it's an identical voltage to the +5V line, I'd say that's strong evidence that you indeed do have a short across lines somewhere, somehow. Do you have a spare computer you could try temporarily, just to rule out a bad computer?

With the TPS connected, you should have ~5V+ on the Vcc (or whatever you wanna call it it's just a regulated voltage rail from the EEC) line, 0V on the ground line, and 0.7V < TP < 0.95V for the remaining line.

[BowTie Eater 5 Liter]

IT WAS A GROUND PROBLEM!!! i grounded the ground wire off the tps connector, and checked the tps voltage, it was at 1volt constantly, thanks guys!!!

[tmoss]

told ya


Glad to hear your running again.

[blackEagle]

Glad you got it fixed!!!

[JulianSerna]

Originally Posted by BowTie Eater 5 Liter

well, i thought my throttle positioning sensor was my problem, so i purchased a brand new one.

what was happening, was the tps was showing 4.79 volts.

i tested all 3 wires
grey wire 4.79ish volts
grey/white wire 4.79 volts also
brown wire 5 volts.

what could the problem be? i replaced the sensor and ive still got the same readings. i can not think of anything else that could be the problem. if someone else could make a suggestion, that would be greatly appreciated.

Thanks, Kris

I played with this problem and did the TPS test, everything. The problem is that the SN95 ECM has a pre-programed parameter called Hi Speed Idle Offset and Another called Active Above VSS. You need to have a tuner change this parameter and set the Hi Speed Idle Offset to 0, rather than the factory 200+ RPM. If you want to confirm that this is the problem, temporarily disconnect the VSS sensor at the transmission, drive around with your Speedometer not working, but notice that this has solved the high idle problem as the ECM thinks the car is at 0 MPH. If this gets rid of your hi idle problem, then you know for sure you need to have a tuner disable the above mentioned options.

I did this on my car and the tuner just changed the parameter on a Diablo Chip and the problem was solved.

Good luck with this ....