91 GT TPS: No Voltage...why?

TheUser · Mar 13, 2004

I've searched and read through a couple posts, but really didn't find an answer. I replaced head gaskets on my car and now the TPS has 0 volts...could have been like this for a while since it hasn't ran since June 03. Either way, I checked the voltage at the connector that the TPS connects into and I know I did it right (green and black wires) because I also have a 90 LX 5.0 and I tested it too and reset the TPS. I'm not real sure how to troubleshoot this...I do have the Probst book, but I want to make sure i'm testing for the right things instead of wasting my time poking wires that don't need to be. Where exactly do I test these at? Any help is appreciated

jrichker · Mar 13, 2004

Code 63 - Throttle Position Sensor (TPS) signal too low TPS . TPS out of adjustment, or 5 V VREF missing, broken wiring or bad connections.

Try adjusting the TPS

Here’s a TPS tip I got from NoGo50

When you installed the sensor make sure you place it on the peg right and then tighten it down properly. Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can move it just a little in very small increments. I wouldn’t try to adjust it using marks. Set it at .97v-.99v, the closer to .99v the better.

(copied from MustangMax, Glendale AZ)

1. Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can and get it nice and warm.

2. When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and the other to ground.

3. Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.

4. Check the procedure for your year, on my 90 I have to turn the idle screw until it just touches the tab, then insert a .010 feeler gauge and give it about one more turn. Then you adjust the TPS voltage to .98v, reset the computer. Start it up, if the idle is to low then turn the screw in until it is just right, then readjust the TPS voltage to .98v and reset the computer and start it up. The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

HISSIN50 · Mar 13, 2004

i would also probe each wire to make sure you have continuity for each of the 3 wires (ground and 5 volts to the sensor, and some juice leaving it on the ref wire). you need to know if the sensor is dead or it simply is not being supplied with the tools to function properly.

TheUser · Mar 13, 2004

yeah thanks...however it's not the TPS installed wrong because the actual connector that the TPS connects to isn't reading a voltage...the TPS could be set wrong and probably is, however, I should have a current from that connector no matter how the TPS is set. I guess I need to back probe the other wiring, but that's what i'm confused with...not sure where to start and exactly how to do it.

TheUser · Mar 13, 2004

HISSIN50 said:
i would also probe each wire to make sure you have continuity for each of the 3 wires (ground and 5 volts to the sensor, and some juice leaving it on the ref wire). you need to know if the sensor is dead or it simply is not being supplied with the tools to function properly.

yeah but the thing is that i've actually tested the TPS wiring and then the connector (3 prong) wiring where the TPS connects to the wiring harness and nothin...so yeah I just gotta start testing other wires I guess....just gotta know which wires to hit and stuff.

Ozz · Mar 13, 2004

Mine is reading .05 after sitting since November and having everything down to the heads removed for upgrades.

Now everyone says to keep adjusting it to get .99 but IT DOES NOT MOVE from .05

Does operating temp make a difference? Because when I was adjusting it, the car would keep dying on me so I was not ever able to bring it to normal operating temp. Before anyone says it, I know the car needs to be set to ON but not running when adjusting the TPS. So that's not my problem. The problem is it reads .05V and will not adjust no matter what I do.

So, the question is, does the car need to be brought up to operating temp before doing TPS setting?

HISSIN50 · Mar 13, 2004

The User: gotcha. what you are planning is what i was trying to say (test upstream of the TPS).
try checking out these pages by TMoss and others. there are several link on EFI, Sensors, and so on at the top of the page.
http://www.veryuseful.com/mustang/tech/engine/

Dave, i dont understand how temp would make a difference, but the tests do say to do it on a warm engine, as i recall. but dont trust my recollection; im hoping someone else can confirm that.
for it not idling, i thought you could idle a car without a TPS. i just thought it was needed for mapping under throttle. what happens if you disconnect the IAC (sorry if that is redundant, i cant remember what all happened and was suggested on your thread. it was long)?

good luck to both of ya!

Ozz · Mar 13, 2004

My car dying didn't have to do with the TPS, it was just a clogged fuel filter

But now I do have to set the TPS and it still isn't moving when I adjust it. But when it idles, it sounds perfect. Some have suggested to leave it alone if it drives perfect, too.

TheUser · Mar 13, 2004

mansonozz said:
My car dying didn't have to do with the TPS, it was just a clogged fuel filter

But now I do have to set the TPS and it still isn't moving when I adjust it. But when it idles, it sounds perfect. Some have suggested to leave it alone if it drives perfect, too.

I had to drill the holes out in my TPS to get it up to .99. It doesn't sound like your problem though, although you may need to drill them still to get desired results. Can you move it around a little and make it change voltages except for .05?

Ozz · Mar 13, 2004

I drilled 'em and it still doesn't move.

I keep hearing the same thing over and over (drill the holes, move the TPS around, etc.), but I DID that already and nothing works.

I even tried 2 other TPS's and all 3 gave the same result. I wish I knew what it measured prior to taking everything apart, I wouldn't be surprised if it was .05 back then too! And if that were the case I'd leave it and forget about it all together.

jrichker · Mar 13, 2004

The VREF voltage (+5 volts) is missing. Two possiblilites:
1.) Bad wiring at the 10 pin connector or computer. You'll need a Chilton's Or Haynes shop manual to find which one of the 10 pin connectors it is, and which pin inside the connector carries the VREF voltage.
2.) Computer VREF failed - not likely.

VREF is also Found on the Orange/White Wire on the BAP or MAP sensor, and on the Orange/White wire for the EGR sensor. It is sourced from the computer on pin 26. Download the diagram from the link in my eariler post to get a complete listing of the computer wiring, sensors & actuators.

Ozz · Mar 13, 2004

FWIW, when I measured the other wire, it measured at 4.9V

Is that extra .1V that much of a big deal? I didn't even move or touch those wires except for unscrewing the TPS from my stock throttle body and moving it to my new Accufab.

TheUser · Mar 14, 2004

Well, I checked voltage at Fuel Pump Relay, MAF, IAB, TFI and Fuel Injector connectors and all were pushing 12 volts, but TPS connector still gets nothing. I used the battery as ground for all of the tests. When I first did the TFI, I was using the Ignition Ground prong thing for ground and got nothing, changed ground to battery and got 12 volts...does this indicate bad ground somewhere like wiring harness maybe?

MansonOzz: Probst says 5V +/- .1V is ok

HISSIN50 · Mar 14, 2004

i would be all over the ground thing if you know that the ground is not sent from the computer. i know the puter sends ground for some stuff, but i just woke up and cannot remember if it does or not. i dont believe it does, or else people would use that wire for testing the TPS. a lot of folks dont.
so if the puter sends 5 volts and gets a signal return, with nothing to do with the ground, i say get to finding the problem. a confirmation from Jrichker, Tmoss, etc is always nice, though.

that would do it though, IMHO.

jrichker · Mar 14, 2004

Go back and re-read my earlier post - you have no VREF. VREF is not the same as ground nor is it the same as the voltage supplied to the injectors or other actuators in the system.

Check for VREF at the MAP (or BAP in speed density cars) and EGR, using the Orange/White wire. Use the Black/White wire for ground. If you get no reading, remove the Positive terminal from the battery and measure resistance between the Black/White wire and battery ground. Do not attempt to measure the resistance with the Positive terminal connected to the battery. If there is a bad ground, you could get a false reading or damage your voltmeter. You should have less than 2 ohms resistance.

VREF is 5 volts +/- .1 volt. VREF is a precision reference voltage supplied to the sensors by the computer. The purpose of VREF is to eliminate errors due to changes in supply voltage such as low battery or high alternator output voltage. Three things get their voltage from VREF: TPS, MAP (or BAP in speed density cars) and EGR. They are all connected to pin 26 on the computer by the Orange/White wire.

stang&2Birds · Mar 14, 2004

Check the orange/white wire for ~5V. Then, check the green wire for between ~0.6v and 1.3V. If you have a Ford TB and have not screwed around with the idle stop, LEAVE THE TPS ALONE AND STOP DOING STUPID @SS *RICER MODS*. As long as the TPS is between the voltages I said, it MAKES NO DIFFERENCE WHAT THE TPS VOLTAGE IS!

The 0.99v myth is promoted by people that KNOW SQUAT ABOUT THE EEC! EVERY SINGLE EEC-IV / V MADE ON THIS PLANET ZEROS OUT THE TPS AT STARTUP! Read Probst, every single Ford tech ever published, read the CPU assembler code, get a tweecer/EEC-tuner, etc.

Note: If you have an AFTERMARKET TB or have screwed with the idle stop, then you must ADAPT the TPS to the POS TB or your mod.

stang&2Birds · Mar 14, 2004

BTW: Ford does/did have some adjustable TPS (sensors). That is NOT the type on the stang! The reason for an adjustable TPS is because the early/cheap systems didn't have the manufacturing accuracy of the newer TBs and sensors. They were a carry over from the EEC III's. Which, BTW, where mega POS systems that were unreliable and were known for leaving cars not running because a simple sensor, like the coolant temp sensor, went bad.

TheUser · Mar 14, 2004

stang&2Birds said:
BTW: Ford does/did have some adjustable TPS (sensors). That is NOT the type on the stang! The reason for an adjustable TPS is because the early/cheap systems didn't have the manufacturing accuracy of the newer TBs and sensors. They were a carry over from the EEC III's. Which, BTW, where mega POS systems that were unreliable and were known for leaving cars not running because a simple sensor, like the coolant temp sensor, went bad.

sorry to say dude, but i also have a nearly stock 90 LX 5.0 w/ stock throttle body...I adjusted the TPS from .68 at idle to .99 and it responds much better and feels better, so take that for what it's worth. On the GT, i'm not even setting the TPS, i'm just checking to see what it's pushing, which is 0 volts at the moment. I do have 12v VPWR at the MAF (Probst said check for VPWR before VREF). I guess now I get to check for faulty sensors causing VREF to be 0...

stang&2Birds · Mar 14, 2004

TheUser said:
sorry to say dude, but i also have a nearly stock 90 LX 5.0 w/ stock throttle body...I adjusted the TPS from .68 at idle to .99 and it responds much better and feels better, so take that for what it's worth.

FACT: The first pre-made pills available in the U.S. were placebos. They came in different colors and shapes. The medical books at the time even had suggestions for which pills "worked best" for some illnesses.

FWIW: I *do* believe that you perceive a difference. However, you're more then free to buy a Tweecer/EEC-tuner download the code from the EEC in your car, disassemble it, and check. No secrets, no space aliens controlling your car, just plain, basic computer control/response algorithms. For over 10 years, people have been able to download and read the code.

Then, there's Probst. Hard to argue with one of the key people in the EEC IV development. Also, the only person that has factory authorized books on the Ford and GM EFI systems. After the EECIV, Probst went on to do the next generation of PCM (EFI controllers) for the vette.

stang&2Birds · Mar 14, 2004

TheUser said:
On the GT, I'm not even setting the TPS, I'm just checking to see what it's pushing, which is 0 volts at the moment. I do have 12v VPWR at the MAF (Probst said check for VPWR before VREF). I guess now I get to check for faulty sensors causing VREF to be 0...

See:
http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Also, check VREF at the MAF/BP and the EVP sensors. Could be a bad EEC or a shorted wire.

Yank the connectors off the sensors and see if there is +5V VREF. If not, you'll need to go to the EEC, yank off the main connector, see if it's shorted to ground, make SURE that the wire you're testing is the same wire as the VREF to the sensors. If there isn't any short to ground, then it's a bad EEC.

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