My 1994 Ford F-150 5.0 Fuel injected engine w/5spd is runningvery rough, surging and rich. I got a code 23 so, I tested the TPS using two methods. One from http://easyautodiagnostics.com/index_ford_4.9L_5.0L_5.8L/index_of_articles_1.php

(I will refer to the internet site as EAD from here on forease)
and I also used the Haynes book as a backup test to confirmthe first test. That’s where the confusion comes in.

Using the EAD method:

Test 1 was checking voltage at the TPS.

I get .02v andit should be .5 – 1.0v with throttle closed = bad TPS

There is novoltage increase as the throttle is opened to full open = bad TPS

Test 2 for 5v reference and I get 4.99v, so voltage in fromPCM is good.

Test 3 for good ground was good too at 12.49v. direct tobattery.

I then used the Haynes book method as a backup test for the EADmethod. The difference in the two is that the EAD method uses the battery asthe ground and test each individual wire on the pigtail side, and Haynes usesthe TPS (green wire) as the check point for ground in the tests. The EAD methodwill not tell you if the connector is the problem. Plus, the Haynes uses an Ohm’stest on the Potentiometer within the TPS.

Haynes test method:

I got reverse readings (negative) with throttle closed of-.97v

Throttle open of -4.59v with a nice smooth transition fromclosed to full open.

When I check the Ohm’s resistance I also get reversed readings,of 88 closed and 3450 open, where as it should be 3 to 4k ohm’s closed and 350ohm’s open.

These negative and reversed readings are confusing me. TheEAD method says the TPS is bad. The Haynes method says it’s good, except the voltagereadings are in negative territory and the resistance is backwards. So is the TPS good or bad? Why wouldthe Haynes method read in negative voltage and the resistance backwards? Myfirst thought was that I had the probes reversed, so I exchanged them and gotthe same results. Is there some way that the arm that slides on thepotentiometer has become dislodged on the throttle shaft and is on the wrongend of the potentiometer?

Thanks for all and any help. This looks like a great site with great people contibuting to it.

 

you should read me TPS thread

 

Both EAD and Haynes tests are exactly the same, the Haynes manual includes resistance values for a good TPS.

Did you check resistance with the TPS unplugged from the harness?

And yea backwards suggests you had the probes reversed, results in the negative.

TPS good or bad? hard to say but looks like you need to regroup do the tests over to be sure of your findings. Who's wire colors did you go by?

Use digrams this page to make sure you know which wire is which and irregardless of color coding found, (Haynes manual might not be right for example).

http://oldfuelinjection.com/index.php?p=30

(scroll down the page)