TPS voltage issue - Need a second opinion.

[festivagt]

Pulled this truck (87 - 2.9/5spd 2wd)out of the bushes and got it running. Had the typical IAC issues causing a high idle. water pump leaked, U-joints were frozen and the brakes were rusted up. Basically I have been going through it and replacing, repairing and putting it back together. I have the engine running REALLY GOOD. I just have one slight miss at idle and the idle seems to stay about 1000rpm. It tries to idle down further but it starts to stumble more and recovers to the 1000 RPM. I have replaced, the IAC - brought the original idle down from 2600RPM, Map, Intake air temp sensor and the TPS. The only thing that changed anything was the IAC. I haven't changed the engine coolant temp sensor - yet. The only reason I haven't is because the TPS at idle with the Diesel screw adjusted out all the way so it isn't touching the plate stop STILL reads 1.46v. I can't get it to come down any more unless I pull the screws out and back it off til it says .8v. when I do - it is so far out I can't put the screws in to hold it. So I guess, am I chasing my tail here with the voltage? is the sensor shit and needing to be swapped again? Or do I even have the right sensor? Or is there another culprit like maybe the engine temp causing a high voltage reading on the TPS? Please advise - most of the time I am the guy everyone else asks - this one has me stumped.

 

[SenorNoob]

Temperature shouldn't have a noticeable effect on the voltage at the TPS. Sounds like the wrong part to me. I wonder if something got consolidated in the aftermarket that shouldn't have?

I would try looking for a TPS from an identical truck in the junkyard. Tho with an '87 that's probably unlikely.

 

[Bird76Mojo]

People in the Mustang world have had to dremel the holes (into slots) in the TPS to get down to the proper voltage readings. Did you also check for a nice clean voltage sweep with no dead spots when you slowly open/close the TPS?

 

[19Walt93]

I like to see as close to 1 volt on the signal return as I can get. Once you make sure the throttle plate is fully closing(I suspect it isn't), you should be able to set the voltage with the movement around the screws without grinding anything. If not, get a new/better TP sensor. There is now "diesel" screw, that's where the base idle is set and it should be adjusted.

 

[snoranger]

People in the Mustang world have had to dremel the holes (into slots) in the TPS to get down to the proper voltage readings.

Generally they’re only moving a tiny bit... Like they’re at .93 volts and they want to get to 1 volt. This ones 1/2 a volt off.

 

[19Walt93]

I could live with .93

 

[snoranger]

I could live with .93

So could I, but I know some Fox body guys that swear you have to be at 1 volt... they can feel the difference.

 

[RonD]

Drill out, elongate, the holes on the new or old TPS so its adjustable down to the .69-.99 volts needed with throttle closed

Once you have it under 1 volt, open throttle wide(WOT) and make sure you are 4.5volt or higher, if not you have the wrong TPS

Also with TPS removed from intake, what is warm idle RPMs?
TPS could be holding open throttle plate

TPS when removed from intake and plugged in should technically have a voltage range of 0 to 5 volts

Yes, it really depends on the software in YOUR computer, as to how the system reacts to any sensors data
Rangers and Mustang probably ran different software in different years, I know DUH, it doesn't mean Ranger won't react the same to same sensor voltage just that it has more to do with the way the software reacts

General sensor info here, and a great read: http://www.fuelinjectedford.com/
Good site to Bookmark!!
For 1994 and earlier Rangers running EEC-IV computers
Select TPS and have a read

 

[bcschief]

The originals in the beginning were slotted and you had to adjust them when you installed them.

 

[festivagt]

Throttle plate closed all the way(visually confirmed with the screw out and NOT TOUCHING The throttle plate) the voltage is at 1.45ish. I can remove the tps screws and rotate the sensor til it achieves the 1v or less, but there is zero possibiliy of putting screws back in to holding the tps from moving regardless of how much slotting you do. I guess I will try swapping the TPS again. Maybe I got a bum one out of the box.

 

[festivagt]

Any ideas for things that would cause a light miss at idle and cause it to idle at 1000k rpm? No vac leaks and a new IAC that dropped the rpm down to where it is. Could the high voltage on the tps cause that?

 

[RonD]

Yes, something is wrong with that TPS, see if you can find a slotted one at wrecking yard, its not a Ranger specific sensor
Usually just the 3 wire plug connector was different from year to year

No, TPS wouldn't cause the high idle, unless it was holding throttle plate open
TPS is used to determine engine "load" and to give the computer a "heads up" when driver wants to accelerate
In a MAP or MAF system there is a delay between gas pedal down/throttle plate open and MAP or MAF reporting decrease in vacuum or higher air flow
This would cause a hesitation and lean mix
On Carburetors an accelerator pump was added to avoid this, it sprayed extra fuel in when gas pedal was pressed down
On fuel injection a Throttle sensor was added, sudden upward change in voltage travels at the speed of light to computer, and computer instantly adds extra fuel so no hesitation
There are 2 voltage levels that matter most for the TPS, under 1volt and over 4.49volts
Under 1volt tells computer to shut off injectors while RPMs are higher than say 1,800, i.e. coasting in gear, saves fuel
Over 4.49volts tells computer driver wants FULL POWER, wide open throttle(WOT), computer will shut off AC Compressor(if so equipped), and ignore O2 sensors, it will run maximum fuel mix from a table in memory, for max. power

Its possible just over 1 volt could cause higher idle, but I have never run into that, there are literally THOUSANDS of software "tunes" used by Ford in their engine computers, so.................
But getting a different TPS that can be adjust to under 1volt will tell you, and me, if you report back, that on yours this was the issue


After engine is warmed up, and idling at 1,000, unplug the IAC Valve
RPMs should drop to 500, or engine may even stall, either is good, it means no vacuum leaks
If idle doesn't drop, then there is still an air leak some where
If it drops but not that low then COMPUTER was setting the 1,000rpm idle, so not a vacuum leak

Motorcraft or Hitachi brand IAC Valves are the only true solenoid type valves, other brands are solenoid/stepper type which will "work" but will always cause some issues, from high idle to wandering idle
Just a heads up
Again if you get a used Motorcraft IAC Valve from wrecking yard it would be better that any new 3rd party brand

 

[bcschief]

I thought he meant belt.

I've never had one of the PS pulleys come off in one piece. I've always had to torch cut them off.

Pulled this truck (87 - 2.9/5spd 2wd)out of the bushes and got it running. Had the typical IAC issues causing a high idle. water pump leaked, U-joints were frozen and the brakes were rusted up. Basically I have been going through it and replacing, repairing and putting it back together. I have the engine running REALLY GOOD. I just have one slight miss at idle and the idle seems to stay about 1000rpm. It tries to idle down further but it starts to stumble more and recovers to the 1000 RPM. I have replaced, the IAC - brought the original idle down from 2600RPM, Map, Intake air temp sensor and the TPS. The only thing that changed anything was the IAC. I haven't changed the engine coolant temp sensor - yet. The only reason I haven't is because the TPS at idle with the Diesel screw adjusted out all the way so it isn't touching the plate stop STILL reads 1.46v. I can't get it to come down any more unless I pull the screws out and back it off til it says .8v. when I do - it is so far out I can't put the screws in to hold it. So I guess, am I chasing my tail here with the voltage? is the sensor shit and needing to be swapped again? Or do I even have the right sensor? Or is there another culprit like maybe the engine temp causing a high voltage reading on the TPS? Please advise - most of the time I am the guy everyone else asks - this one has me stumped.

Have you checked your VREF voltage ? Should be about 5 volts.

 

[mnewman]

Look at the connector on your wiring harness and then the TPS. Check where the reference or tab is on the connector v the TPS. I bet you did the same thing I did and got the wrong sensor. I was getting a reading of like 1.5 v.

Here is a link to my youtube where I start trouble shooting. Hopefully I'll get part two done where I waste a ton of time trying to slot the connector screw holes before I looked at the connector and realized it was the wrong damn part. 5:30 is where the voltage comes up.

 

[89Twincharge]

If it's been in the bushes the you should clean your grounds and or replace both battery cables before you do any electrical test.