I have replaced the Throttle Position Sensor, Map Sensor and cleaned the Throttle Body and the Air Flow Sensor but I continue to get a low voltage code on the Throttle Position Sensor. Truck will start and idle like a new one but if you try to accelerate it will bog down. If you gradually depress the accelerator the truck will get up to normal speed fairly quick.I have been unable to find anyway to adjust the voltage on the Throttle Position Sensor. This is a 1990 F150 XLT Lariet with the 4.9 in line 6, EFI. Any help on resolving this problem will be appreciated!

 

Did you get a Motorcraft TPS? I had a cheap one fail by low voltage (code 63)

Test the TPS, and make sure the reference voltage is 5v.

Are there any other codes? And based on your symptoms, a fuel pressure test, (idle and under load) would be wise.

 

There is no adjustment on the TP for your 1990
The older ones in the mid-eighties did have adjustment slots
That reference voltage is the key like Junktownbill99 mentioned
The wide-open throttle spec of 4.5 volts is correct? right?
.8 to 1.3volts low (idle) and 4.5 to 5 volts high (WOT)

 

My guess is you have the TPS tabs on the wrong side of the throttle shaft tabs. That will force the sensor to read closer to zero volts/ below min voltage and not move toward 5v when the throttle is opened.

 

Not sure you can do that
IIRR
You can't line up the bolt holes with the tabs on the wrong side (with the correct TP)
And / or, it will break the TP sensor when you hit the gas
If you get the wrong TP, you sure can (install the tabs on the wrong side of the shaft flats)
They make those TPs that are spring loaded both clockwise and counterclockwise Taurus/ Mustang VS trucks etc.

 

You sure can install it on the wrong side of the tabs. I have done it in the past which is why I look through the window on the sensor to make sure the sensor is turning with the shaft before reinstalling the throttle body. If you apply very little twisting force the holes will line up.

Not at all. The tabs on the throttle shaft will move away from the TPS tabs so the computer will think that that throttle was never opened.

 

There is also a small circular bushing that keeps the TPS centered, did you lose it?

 

If I remember correctly the ‘94 had one but no bushing on my ‘87 and ‘89.

 

My 91 has one, however they don't give you a new one with the TPS.

 

I beg to differ
That will break the TP internal gears
They only line up one way and be spring loaded
They are idiot proof when it comes to installation

 

Agree to disagree.

 

I have a few spare TP's in my box
I will try what you say next time I have one off
I sure do not know everything and just learned something else the other day on Silverados
In this business, the day you quit learning is the day you die

 

Clearing the codes on a dreaded valve body issue on an Allison transmission
Little piles need a new valve body and GM says 6 months and 6000 bucks or north of
Love those Duramax's, keeps me in groceries
Note: What I learned
You need to press the start button for 20 seconds to access the accessory position to clear codes
His was saying the code was cleared but was still in reduced power mode and starting out in 3rd or 4th gear
Big problem, big pile

 

The TPS is after market. I will do the test on it. There are no other codes. Thanks.

 

My TPS will only fit one way. If I locate the tabs in the wrong position it won't turn. Thanks!