1998 yukon Mystery p0300 and rough idle still

[exp500]

From post #305 0.045 plug gap.
Did you repair the O2 sensor you were having pronlems with? It was a downstream so shouldn't affect fuel trims much.

 

[OilBurner2003]

From post #305 0.045 plug gap.
Did you repair the O2 sensor you were having pronlems with? It was a downstream so shouldn't affect fuel trims much.

Testing checks out with power and ground, threw a spare sensor in and it’s still stuck a .450. It’s beyond me at this point, I have no clue what it could be.

 

[exp500]

PCM electrical connectors have been removed and looked very clean, engine grounds have been cleaned very well near front of engine to transmission, some were covered with oil, no change afterwards. also did a computer “Drain” As a last ditch attempt, noticed no results after idle and warmed up. The fuel pressure topic, according to other members of the forum 55 PSI running is good. Maybe that’s correct, maybe it’s not. You guys know more about it than I do. I’m not too hopeful to figure it out, but maybe I could do a trip and get some fuel trim data and such as well just to see what comes up. Fixed the exhaust leaks I had except for the downstream yesterday, for some reason I can’t get it to not leak. It’s a downstream part towards the muffler, but at least it’s not the upstream. Not the primary concern anyway.

If I was to regap the plugs for a test, what would you suggest?

Those answers help me eliminate possibles. Thanks. Fuel pressure results moving around still bother me. @east302 's post about fuel trim ,O2 and missfire counts is the way to move forward . Hoping for fresh scans.
Put a plug in your heater valve line to eliminate leak till you find parts.

 

[OilBurner2003]

Those answers help me eliminate possibles. Thanks. Fuel pressure results moving around still bother me. @east302 's post about fuel trim ,O2 and missfire counts is the way to move forward . Hoping for fresh scans.
Put a plug in your heater valve line to eliminate leak till you find parts.

Roger, I’ll report back when I get the time to do it.

 

[exp500]

Testing checks out with power and ground, threw a spare sensor in and it’s still stuck a .450. It’s beyond me at this point, I have no clue what it could be.

If I remember correctly, it was a Walker O2 sensor. Swap downstream sensors or replace that one.Denso's work good. Regap plugs first.

 

[B-train]

What a morning. Long story short, got the truck back. Said he didn’t have time to look at it anytime soon. Got it back home and already tore the damn thing apart, I’m just too curious. In the picture is part of the wiring harness that has a burn underneath, I’d have to take off that wire Loom to get a pic. Not sure how to either.

Sorry to jump in late. What is that connection rubbing/burning on? Is it possible the connector failed internally?

 

[OilBurner2003]

Sorry to jump in late. What is that connection rubbing/burning on? Is it possible the connector failed internally?

Hello sir, it’s rubbing on the EGR tube. Was I should say.

 

[B-train]

Hmmm....I wonder if that is playing into it. Melted stuff can cause weird issues

 

[OilBurner2003]

Hmmm....I wonder if that is playing into it. Melted stuff can cause weird issues

I have taken the wire harness apart and inspected the wires. None look burnt, but it’s not out of the question that they could have gotten hot I suppose, need to look at it all again.

 

[B-train]

I'd look at the pin connections to see if one or more have gotten distorted due to heat, therefor making a poor connection. Look for expanded metal, burn marks, etc. Try closing them up if possible to close on the pins tighter of you see something