While you are troubleshooting the HEGO circuit, I recommend you verify the Heater Ground connection as well.

Check the Black wire in the vehicle harness for continuity to ground. Also when checking for 12v on the heater positive use the Harness Heater Ground wire in your measurements.

 

So, that Gy/Y wire from the O2 sensor may go to one of those F-Links under the Dash (F-Link "X", Blue, 20 gauge link) then on to the Key switch.

May be a little larger Gy/Y wire coming off the key switch, 12 Ga, then tru the F-Link, then 16 ga, Gy/Y to HEGO.

There may be a splice where the GY/Y wire comes off the key switch, one wire goes to the F-link,and the other goes to the fuse box, all GY/Y in color.

 

Well I believe I have found the culprit (hopefully). Found the fuse link with 3 GR/Y wires which was a major PITA. One goes to the fusebox as you said, and it looks like one goes to the ignition. Im assuming the other leads to the HEGO. Ive taken a picture to verify but the fuse link looks fried to me. Now can I just run an inline fuse or delete this thing all together?

 

Well Done Lad !!
I would put a fuse back in there. That F-Link, if blown, protected your harness wires from, I'm guessing, a failure or short in the HEGO Heater circuit.

fuse size?

Which wire is coming from the Ignition ?

For testing purposes, use a 30Amp for now.....

 

Well of course I got excited too soon. The f-link had continuity across it so that wasn't the issue. What I have found surprises me tho. I tracked the wire from the HEGO and had continuity all the way up until the firewall plug (huge connector). When I checked the interior side of the plug, I found that the matching GY/Y wire was nowhere to be found. It was missing. Checked the wires from the fuse panel side; (Fuse 5) is where the GY/Y wire appears and is connected to two purple/orange (maybe purple/red). The GY/Y wire coming from the fuse panel connects to the fuse link and splits into two GY/Y wires. I have tracked one to what looks to be a square connector going to the steering column (I'm assuming it runs to the ignition). The other gets lost into the dash somewhere, I couldn't track it without removing the entire dash. Does this sound right??? I found where one of the Purple/orange wires connects to the firewall plug and I am tempted to splice the engine bay side GR/Y with the Purple/orange wire to see if that gives the sensor power

 

Here you can sort of see the GY/Y wire entering the fuse panel and connecting to the 2 purple/orange wires

 

I would probably investigate a little more.

Did you measure 12v on the wire that; “gets lost into the dash somewhere“ ?

 

Is the GY/Y wire from the Ignition Switch a larger Diameter than the GY/Y wire that; “gets lost into the dash somewhere“ ?

 

I went ahead and spiced an inline 30 amp fuse from the large diameter GY/Y on the engine bay side to the Purple/Orange wire on the engine side and it ended up removing the 41 code from the KOER test. Everything passed! I measured mid 14 volts (my battery is bout shot) at the O2 sensor heater wire!! I also checked voltage on the signal wire at the computer and got .8 volts idling about 950-1000 rpms. Revved it up at the throttle body aiming around 2000 rpms (by ear so not very accurate) steady and it bounced around .3-.6ish volts. It's running a lot better now when I have it with the timing at around 10 degrees (i will verify tomorrow with the timing light) and the Spout in than it did....but still stumbles under a load. Not near as bad but still does pretty bad. I have noticed some of my vacuum lines are a little dryrotted so I've ordered some new hoses and they'll be here Wednesday. In addition to the hoses, I've ordered a new cap and rotor button and new plug wires. I feel good about the vacuum lines helping
I didn't pull the entire dash off and the wire bundle went up under the top of the dash which was out of reach for continued tracking. If I had to guess it looked like the bundle was going to the radio/air controls/etc. If I could have pulled the entire dash off it would have made the job a lot easier but the weather is nasty with this storm front rolling in (perfect deer hunting weather, couldn't keep this off of my mind though) and I'm doing this in my driveway by myself. I'm literally losing sleep over this truck haha

 

I'm guessing that off the assembly line, there was a matching/corresponding wire on the interior side of the plug.

It may be too big of a job to fix that, so you could tap into the wire that; “gets lost into the dash somewhere“ , and run it out to the wire on the outside plug.

 

Does this sound like the vacuum line be be causing the stumble? Kind of sounds like it's starving for fuel under load. And from what I'm learning, a little vacuum leak will cause a higher idle, correct? I pulled the hose off of the FPR and no fuel came out. I plugged it with my finger and it didn't seem to affect the motor, at least not much. I want to install a fuel pressure gauge on the fuel rail at the Schrader valve but cannot find the correct fitting. Do you happen to know the size of the hole if I pulled out the shcrader valve adapter?

 

I had a hard time finding the correct adapter for mine too, I was about to order one online because every rental kit from the auto parts stores in my arear had the adapter missing. I was lucky enough to find out my mechanic neighbor had one. You might have to order one online.

 

I have looked everywhere online and cannot seem to find one. I must not be searching correctly. I'll take another look today. Jegs has one that is a "kit" that is for mounting to a 5.0 fuel rail. Think it will fit?

http://www.jegs.com/i/JEGS-Performan...41046/10002/-1

 

The ones you tried, were they to big or to small ?

 

I would add approx $15 more, and buy a test kit usable on multiple vehicles.