99 Ford F150 Shifting hard error code po120 replaced TPS with no luck.
Hi all,
I own a ford f150 1990. It is a 4.6 Liter. About a year ago I had a junk yard transmission put in. The truck has run fine for a year, however lately it has been shifting hard. I have been getting code po120, which deals with the TPS. I did a tune up, replaced plugs and wires, and changed the TPS sensor. I am still getting a hard shift. The RPM's go up high around 3 1/2, and then it bangs in hard. Anyone have any suggestions as to what I should do now?
It could affect the shift point because the PCM depends on it for a reference along with some other sensor inputs to tell the transmission when to up shift [what you are doing with the throttle].
I would check the voltage output on the lead back to the PCM that should have the throttle angle position variable voltage on it.
Use a voltmeter on a 5 volt scale or close and measure between the variable output and the negitive side (return) usually a black lead and "not" the chassis.
You should see approx 1 volt or less at rest to about 4.5 volts +/- at wide open throttle angles.
If ok and not intermittant you may have a code set for a transmssion fault as detected by the PCM.
Does the OD lamp ever flash?
Good luck.
I am not sure what you mean about the throttle. I have not done anything to it as of yet. There is three wires that lead to the TPS. One of them is black which I presumed was the ground. I took my Voltometer and put it on a scale of 20 volts. I went from the black (ground) wire to the other two which I got 4.7 volts for each wire. The truck was running at idle. I should also mention that it runs great at idle. I will try and check what the voltage is going back to the PCM tommorow.
Your in the right place.
The black is the 'return'. It is not ground. That is why you must measure to that lead as the negitive reference.
The high side should measure the 4.7 volts +/- as you found.
The other output lead needs to measure in the area of about .9 to 1 volt at idle or closed throttle.
This value should rise as you open the throttle becasue it's this rising value that tells the computer what you are doing with throttle as you drive otherwise the sensor would be useless.
Make this measurement with key on, engine off, so you can open the throttle full to see what the voltage does.
The TPS signal does a lot of control functions with just it's varying voltage as you drive.
The computer uses this signal in part to determine when to upshift, when the EGR can be allowed to open, what to do with fuel injection on decelleration, how much extra fuel to add when you call for fast throttle response, when to unlock the transmission converter, demand or load down shift control, and other control functions such as updateing the computer tables in times of decelleration when the computer has the least to keep track of.
Good luck.
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