1998 yukon Mystery p0300 and rough idle still

[exp500]

GM/Delco.Delphi ICM/Coil/CPS/ Cap/Rotor can use United DCR-820X cap also. Denso/GM O2 sensors, NGK/ AC plugs,Packard/GM/Delco wires.These are the only ones I know work. Maybe plug wires worn/damaged. Try swapping coil wire, it gets 8x overworked. Are plug/coil wire ends Fully seated in cap? Most plug wires are not bonded boots so they slip. I've pushed a few in with small screwdriver on metal to fully seat. Wiggle ICM/CPS/Coil connection wires while at idle looking for change.Next would be Dist cap/rotor/wires/plugs.
Have you tried the water spray bottle at night fogging ignition wires/parts? O2 sensors are OK until miss gone.
Try to reduce /eliminate miss, look for a change for the better to point towards solution.

 

[OilBurner2003]

GM/Delco.Delphi ICM/Coil/CPS/ Cap/Rotor can use United DCR-820X cap also. Denso/GM O2 sensors, NGK/ AC plugs,Packard/GM/Delco wires.These are the only ones I know work. Maybe plug wires worn/damaged. Try swapping coil wire, it gets 8x overworked. Are plug/coil wire ends Fully seated in cap? Most plug wires are not bonded boots so they slip. I've pushed a few in with small screwdriver on metal to fully seat. Wiggle ICM/CPS/Coil connection wires while at idle looking for change.Next would be Dist cap/rotor/wires/plugs.
Have you tried the water spray bottle at night fogging ignition wires/parts? O2 sensors are OK until miss gone.
Try to reduce /eliminate miss, look for a change for the better to point towards solution.

Plug wires are fully seated, if I was to replace them it would be the fourth time I’ve done it. Dist cap is AC DELCO, rotor is AC DELCO, wires too. but no, I haven’t sprayed it at night.

 

[exp500]

What spark plugs and what Gap?

 

[OilBurner2003]

What spark plugs and what Gap?

Ac DELCO at 60. gap.

 

[exp500]

I've been gapping mine at .045 and easily go 40k miles, I don't burn out caps like before. There may have been a TSB on it (gap), I don't remember how to find it.

More Information for NGK 3403

 

[OilBurner2003]

I've been gapping mine at .045 and easily go 40k miles, I don't burn out caps like before. There may have been a TSB on it (gap), I don't remember how to find it.

More Information for NGK 3403

All that I know is that most people/Manual say 60. Is stock. I’ve heard of people changing the value to get better results, but I’ve never tried it.

 

[exp500]

I suggested it due to your symtoms, and it takes another 10k volts to jump larger gap. What I would really like to see is how your fuel trims and misfires look under load at speed. I reread most of your posts, and fuel pressure is still a big concern for me not knowing how far you went through the testing procedure. At one point you said 62#KOEOFF. The other possible cheap fix is disconnect battery, pull ECM plugs from computer and look for water or corrosion. Clean(deoxit spray or maybe brakekleen lightly) add a small amount of plug boot grease around terminals and grease rubber seals too. Engine grounds especially the braided one by trans dipstick are also suspects. Your DVOM meter can test those grounds to battery, except for the braided one. Test that from both ends. ( means you might as well replace it cause you gotta remove it to test).

 

[east302]

Can you post a recap for us on your scanner readouts? I’d have sworn that you had screenshots in here somewhere but the IFS syndrome may have kicked in on me.

*Fuel trims at idle and at, say, 2000 and 3000 rpm if you’re not able to drive it
*O2 sensor graphs
*Misfire counts by cylinder, idle and raised rpm

Did you fix the broken vacuum lines going to the heater hose water valve and solenoid? Potential vacuum leak…maybe.

 

[OilBurner2003]

I suggested it due to your symtoms, and it takes another 10k volts to jump larger gap. What I would really like to see is how your fuel trims and misfires look under load at speed. I reread most of your posts, and fuel pressure is still a big concern for me not knowing how far you went through the testing procedure. At one point you said 62#KOEOFF. The other possible cheap fix is disconnect battery, pull ECM plugs from computer and look for water or corrosion. Clean(deoxit spray or maybe brakekleen lightly) add a small amount of plug boot grease around terminals and grease rubber seals too. Engine grounds especially the braided one by trans dipstick are also suspects. Your DVOM meter can test those grounds to battery, except for the braided one. Test that from both ends. ( means you might as well replace it cause you gotta remove it to test).

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?

 

[OilBurner2003]

Can you post a recap for us on your scanner readouts? I’d have sworn that you had screenshots in here somewhere but the IFS syndrome may have kicked in on me.

*Fuel trims at idle and at, say, 2000 and 3000 rpm if you’re not able to drive it
*O2 sensor graphs
*Misfire counts by cylinder, idle and raised rpm

Did you fix the broken vacuum lines going to the heater hose water valve and solenoid? Potential vacuum leak…maybe.

Will go get that info for you guys later, o2 graphs misfire when I get the time.

Heard another person say the vacuum lines on the heater hose valve didn’t affect engine performance, like it wasn’t apart of the same system…I need to get a new hose for it soon. It’s cracked and such.