TPS 10 volts!?

[DOOD_95]

First, thanks to you all for the info/enthusiasm I've read for the last couple of years. This is the first time I've posted anything as I have always been able to find what I needed to keep my Ranger running before. If I simply did not find the right thread or tech article or something I apologize, I'm really just not that great at this whole computer thing in the first place.
I have a 1994 Ranger 4.0, automatic. Idle is fluctuating and 1st to 2nd shift happens at the wrong time and often flutters as it shifts if your accelerating. If you hold the pedal steady at a very low amount of throttle it'll shift smooth, then you can accelerate all you want through the rest of the gears. If you push the pedal beyond the "downshift" resistance spot however it'll cut the engine for about a second or two or until you lift the throttle. As long as you never pass about half throttle, it drives great, if you do, it cuts out/"resets"/cuts out/"resets" steadily.
Checked tps, base voltage is right, sweeps smoothly as the throttle is opened, however continues to increase voltage throughout the sweep up to a hair over 10volts. Check tps on another truck. Works/checks properly. Checked power supply to the tps, reads a bit over 10volts.
Any suggestions here? I'm finding what to do if the voltage is low but not if the voltage is crazy high. Thank you all in advance for your help!

 

[SenorNoob]

Since the TPS gets a 5.0 (gave or take a tenth) volt signal from the ECU that it then cuts farther to send back to the ECU, I'd say you have a crossed wire or 2 wires with the coating missing from both and rubbing together.

So, my official suggestion is to check the wire powering the TPS. I believe it also powers a few other sensors.
Edit: I suppose that means the there could be some kind of fault in one of the other sensors allowing power to bleed through from a 12v circuit. Only thing that comes mind as possible having both voltages to it though is the MAF and I'm not sure about that.

 

[RonD]

Yes, 5volts should be at the TPS.
Check the ECT sensor, I think it is powered from the same voltage regulator in the computer box.

ECT is a 2 wire sensor on the intake near the t-stat housing, TWO WIRE, not the 1 wire temp gauge sender.

 

[DOOD_95]

I'll start chasing those down tomorrow morning. I'll let you know what I come up with there. Thanks!

 

[DOOD_95]

According to the schematic for the underhood wiring that I have found for this year/truck/engine/trans set up, the brown/white wire feeds both the TPS as well as the DPFE. I'm not finding anything else that shares the brown/white wire. Hopefully it'll be that simple and I can at least isolate it to one wire. Otherwise I'm thinking I'll have to separate all the wires going to all the other items to check and see if it's bleeding back. Just got an iceball storm this morning after several sunny beautiful days so I'm not really super excited to go out there until later when this is supposed to blow through. I'll keep posting new info as I have it.

 

[Andy D]

Yah please follow up. Electrical gremlins are a PITA. I look at stuff really carefully. Because, it is easier than using a meter. In older cars, the vinyl wire jackets, get brittle and stiff It shrinks, putting stress on the ends. Add a little water , some dirt and oil. Vibrate. Gremlins. It is an age problem..

 

[DOOD_95]

OK, update time. Traced the brown/white wire from the TPS all the way to the PCM. Actually found TWO spots where it was rubbed through. One with another wire (yep reading full voltage - to what I have no idea, it's taped now though) and the other rubbed through spot was seemingly not contacting anything else and couldn't figure out why it looked rubbed through and the multitude of wires around it looked fine. That spot is now taped as well so no big deal there. TPS no reads as it should in voltage and sweep. Engine still runs like crap, idles like crap, cuts out under a load. NO CHANGE WHATSOEVER. I can't imagine it was a bad thing to remedy but I have to admit I'm extremely bumed it didn;t even change something let alone fix my issue. Apparently I hit bullseye in a target other than the one I should've been aiming for... I do get different codes now. Now it reads MAF low voltage. Checking that this evening when I get home (thank God I own enough Fords to be able to be messing with this one and not being on foot). I'll check back in when I figure out what the MAF check has in store for me.

 

[pjtoledo]

Mafs use the same 5.0 volt reference voltage as the TPS.

 

[RonD]

OK, update time. Traced the brown/white wire from the TPS all the way to the PCM. Actually found TWO spots where it was rubbed through. One with another wire (yep reading full voltage - to what I have no idea, it's taped now though) and the other rubbed through spot was seemingly not contacting anything else and couldn't figure out why it looked rubbed through and the multitude of wires around it looked fine. That spot is now taped as well so no big deal there. TPS no reads as it should in voltage and sweep. Engine still runs like crap, idles like crap, cuts out under a load. NO CHANGE WHATSOEVER. I can't imagine it was a bad thing to remedy but I have to admit I'm extremely bumed it didn;t even change something let alone fix my issue. Apparently I hit bullseye in a target other than the one I should've been aiming for... I do get different codes now. Now it reads MAF low voltage. Checking that this evening when I get home (thank God I own enough Fords to be able to be messing with this one and not being on foot). I'll check back in when I figure out what the MAF check has in store for me.

Did you reset computer?
Disconnect battery for 5 minutes, computer needs to relearn new voltage.

And if you haven't yet I would certainly check MAF voltage, and clean it.
MAF is the main fuel/air mix sensor, bad data from this will cause all your symptoms.
EDIT:
Forgot to add this link about MAF testing and cleaning
http://www.therangerstation.com/tech_library/CleanMAF.shtml

 

[Andy D]

Wild guess, Could the 10V fry something looking for 5V only? Can you test the TPS?

 

[SenorNoob]

That's certainly possible. Not likely the TPS tho as it's just a variable resistor. If it failed there should be no output whatsoever. However there does seem to be some kind of circuitry as part of the MAF sensor. Because it is possible for it to put out both low and high voltage at the same time when it goes bad.

 

[DOOD_95]

Update/answer: RonD, I did reset the computer both by battery disconnect and by ending the OBDI scanner test mid second test (according to the instructions, this erases codes and flashes the system - not sure I beleive all that, the OBDI functions seems a little twitchy on that unit compared to the OBDII functions but I did both to be sure) Checked the MAF, it tested ok according to the testing procedure here. I swapped it with a new one from another 4.0 ranger (common MAF I know but it's nice to have another ranger available to me to swap parts back and forth for doublechecking) and tested it as well. No change. New one from other trucvk tested identically on both trucks (also swapped/tested this one onto the other truck tested same/good ran smooth). Everything now tests good on the truck but nothing seems to help. Ran the codes again as after a really bad stall the CEL returned. DTC:111 System Pass. Seriously. With the light on and running like crap. I think I'm going to go bang my head against the wall for a while it'll feel better/less frustrating/more productive. Then maybe too I'll sleep better and wake to find this whole thing to've been a bad dream. I am ALL EARS as to anything you all could suggest. I am fresh out of ideas and running dangerously low on patience with it.

 

[RonD]

Well I guess you are down to a bad circuit in the Computer.
Have you pulled it and checked the connector?
Those can get wet and corroded, also the grounds around the computer getting loose or corroded this causes issues because the computer uses grounds to control most things.
Since warranty isn't an issue you can pop the top and have a look inside, if a circuit has been damaged you will often see it as a burned spot.

 

[DOOD_95]

Agreed.

I agree. This is unfortunately starting to look like a computer problem. Sure do have a lot of shiny new parts to show for it! Thankfully my daughter's Ranger is a near mechanically identical truck (hers runs, not totally identical). I'm thinking of swapping the computers while she's not looking and seeing if the problems magically jump from mine to hers. She is not going to be driving her Ranger for the next couple days as the weather is supposed to be dropping like a rock tonight from 50° right now, to freezing drizzle to snow and 10° high/ 0° low. She'll be taking the Bronco for sure...hmmm.

 

[DOOD_95]

Quick update: I had left the truck with the battery unplugged for two or three days while I'm waiting this snow out and had a few minutes to spare yesterday. Well, Ford finds work for idle hands so I went out and reconnected the battery and started the truck to see if the extended period of being diconnected would perhaps have given it a better time to clear its thought and straighten up. Sadly no. Quite the opposite actually. It won;t even stay running now. It idles terribly rough unless you coax a bit of RPM out of it then as soon as it reaches a steady healthy sound through maybe 1000-1500 RPM it dies and may or may not want to even try to start again. It's seriously getting worse with each new part or repaired wire. I'm thinking I should've broken several additional items so it would run better. Still haven't had the opportunity to swap the computers but I'm afraid it may self distruct. I think it's the only step in the negative direction left.