First time poster and newbie to Ford Trucks

I have a 1999 Power Stroke that had some erratic throttle response a few months ago. I have not driven it since and today I started it back up to find there is no throttle response now. When the gas pedal is pressed the service engine soon light turns on and then goes away a few seconds after. I found a few posts here that were helpful in troubleshooting but nothing for a fix yet other than to replace the 250 dollar pedal assembly.

I removed the pedal assembly and used my meter to measure resistance on the TPS and found that as the peddle is pressed the resistance is a nice gradual increase as I would expect. Are there specific values I should be looking for as "good"? I also tested the IVS and found that it is .01 ohms when the pedal is not pressed and overload when the pedal is pressed as I would expect. I checked the fuse for them and found it to be good. I checked for voltage when truck is running on both sensors and found the 5VDC on the TPS and 12VDC on the IVS. I also inspected for bad/chaffed wires and found none.

Is there something I am missing here? All the symptoms I am experiencing seem to point to one of these sensors but testing them shows they are working correctly. I am tempted to just buy a new pedal assembly but since its 250 dollars I would like to make sure there's nothing else I can look at.

thanks in advance for any replies!

 

It's always best to diagnose an Electrical Load while in the Circuit. The best way to accomplish this is to reinstall the Unit and use Back-Probes with the Engine Running to monitor while moving the Pedal. You should see Voltage increasing while moving the pedal (Potentiometer). The IVS either has 12VDC or 0VDC i.e. On/Off, Open/Closed.

Most likely, based on your description of the OHM's across the Circuit, you're looking at a connection issue rather than a Mechanical issue.

 

So I finally got some back probes and tested and tested some voltage's. All measurements were taken at the back of the wire harness connectors so that I was testing the connection points as well as the sensors themselves.

When key on engine off the IVS shows 11.87 to 12.32 VDC when the accelerator pedal is not pressed in. As soon as I press the accelerator pedal in the voltage drops to .01 VDC. I repeated this multiple times and it switched every time. When key on engine running the IVS shows about 13 VDC while at idle and .03 VDC when the accelerator pedal is pressed in. After pressing it a few times the highest I ever saw the IVS was 14.26 VDC at idle.

The TPS always showed a reference voltage of 5.03 VDC. At idle, the signal showed .69 VDC. As I press the pedal it gradually raised up and maxed out at 3.84 VDC. I did find that when measuring resistance on the signal circuit of the TPS that it was 548 ohms at idle and gradually worked its way up to 1.18 ohms when it was about 95% of the way pressed down. However, the last 5% of the pedal made the resistance value dropped to 1.05 ohms. I had to be moving the pedal very slowly to find this out so I could not recreate this with the voltage.

I also bought an OBD2 and downloaded forscan on my computer. P0221 is the code being thrown when the throttle response is gone. Using the graphs feature I was able to test live and find that the ivy s changes state everytime the pedal is pressed even when the check engine light comes on and there is no throttle response. However, the throttle position is kind of wacky on the graph when there is no throttle response. Sometimes it shows movement other times it stays steady.

I'm thinking it's my TPS which would be a nice because it's only $30 or so. Should the signal voltage ever get up to 5 volts? Or do all of these reading seem normal for both sensors? I suppose it could be a connection issue but I could not get any consistent results when jiggling the connectors for both sensors and pressing the pedal in. I'm also curious if the slight jump to 14.26 VDC for the IVS is normal.

Thanks for any help anyone can provide. Back to research for me.

 

Hi, I know this is an old thread but How did you back probe the Harness and how did you know what values when to sensor?

 

Paging @BBslider001 ...

I believe it was Byron that recently became an expert on the IVS and TPS, if not hopefully he will remember who it was.

EDIT: Seeing John post just below me, maybe it was @Colorado350 ...

 

Here’s a video I used. I got lucky with just cleaning the IVS. There’s multiple videos on YouTube if you continue to need help