Rough idle is back with vengence

[smokey_mountain]

Good folks of this forum,
while my other thread is locked, I have to open this one.

This is a problem for technically-curious, it is far beyond my troubleshooting ability.

Situation:

• Idle was relatively smooth with AC off season(and some other improvements)
• With light feather throttle tip in between 40-50 MPH to maintain the speed uphill engines pings even on 89
• Now AC back on and last night truck was shaking and rocking so that my wife called me asking to come over as she was afraid it would stall
• Mode $06 shows 3 misfires only across all 8 cylinders (much better than with original spark plugs)
• Fuel is Exxon 89 from 3 different stations
• No codes or MILs
• I have noticed that shaking and vibration is more noticeable as tank gets closer to empty, no idea if it has any bearing on fuel pressure, but again, no codes of any kind
• Just a reminder, I did new OEM plugs, new wires, new engine and transmission mounts, new OEM air filter, new oil change.

Appreciate your thoughts/ideas. I am 11-14 months away from my next truck, that is how long it takes to get that Kia, so I need to get this truck to run.

My logs are here https://docs.google.com/spreadsheets/d/14_bFRJg-Ew5v__t3jPefyXJLdsCx6D8YC-SclhXSGo4/edit?usp=sharing

 

[OR VietVet]

Care to refresh the year, make and model?

What the hell is a KIA?

 

[smokey_mountain]

2018 Yukon 4x4 5.3 stock

 

[OR VietVet]

I don't recall all of the other thread but are you still in your drivetrain warranty period at the dealer? At least the emissions warranty.

 

[smokey_mountain]

Full bumper to bumper, truck is < 1 year old. Old adagio from all dealers, no code - no repairs. I have tried even arbitrage, was told, it goes from point a to b and it does not stall. It is within GM oeprating spec.

I don't recall all of the other thread but are you still in your drivetrain warranty period at the dealer? At least the emissions warranty.

 

[OR VietVet]

********, if they can drive and feel the problem then they have to stand behind warranty. Ask/tell them that you want to talk to a higher up. That would not fly with me but then again, I can be very convincing when I get pissed off. You know, big guy at 6'4" tall and weigh in at 310 lbs. and am 67 years old, so I got all day to tell them what I think of them. Especially as a former ASE Master Tech.

It almost sounds to me like you have a vacuum leak.

 

[smokey_mountain]

yes, you are who the dealers here need to meet, they can't care less about feeling it, I got Attorney General, DMV talking to them and they just smirk, Arbitrage decided in GM's favor, saying not severe enough it does not stop and does not prevent safe operations, they said all GM trucks are like that some worse than the others but they all rough idle. They brought 1 truck and it was smooth, they brought another and it was rough...

********, if they can drive and feel the problem then they have to stand behind warranty. Ask/tell them that you want to talk to a higher up. That would not fly with me but then again, I can be very convincing when I get pissed off. You know, big guy at 6'4" tall and weigh in at 310 lbs. and am 67 years old, so I got all day to tell them what I think of them. Especially as a former ASE Master Tech.

It almost sounds to me like you have a vacuum leak.

 

[OR VietVet]

Ok, you can start with some basics. MAF cleaning or replacement and clean throttle body. Get a fuel pressure reading asap. How does it do if you try another fuel source? Keep tank above 1/2 tank for now. Consider 1/2 tank as empty. I never allow tank to get below 1/4 full. You have to remember that fuel pump is cooled by fuel around it. Spray water around the top engine and intake area, while running, to see if rpm steadies or picks up if you find a vacuum leak. If you have a mechanic's stethoscope you can pull the probe out of the end and listen for it as well. Run some injector cleaner thru it since you could have a fuel feed problem caused by junk in the system from running tank too low. You may also have a problem with the wires if you did not install right or used aftermarket wires. You said OEM plugs and then just said wires. You could also have an intermittent problem with the coils. Check all connections and make sure there is not a spade pushed out of a connector that is making intermittent connection.

https://www.rockauto.com/en/moreinfo.php?pk=7188700&cc=3438501&jsn=2187

https://www.rockauto.com/en/moreinfo.php?pk=8445304&cc=3438501&jsn=2219

https://www.rockauto.com/en/moreinfo.php?pk=8101696&cc=3438501&jsn=2239

https://www.rockauto.com/en/moreinfo.php?pk=6309438&cc=3438501&jsn=2170

 

[smokey_mountain]

Thank you, I did not think about pump cooling. Rough idle worsening so far has been correlated by my observations with tank running below 1/2 and obviously running AC. Wires, plugs are all bought from the dealer - genuine AC Delco products.
Couple of questions:
1. When you say pressure reading do you mean OBD II scanner reading while running?
2. Spraying water around what areas. I am not familiar with vacuum leak diagnostics?
3. I was thinking about coils too, but was told earlier in another thread that coils would cause misfires?

Ok, you can start with some basics. MAF cleaning or replacement and clean throttle body. Get a fuel pressure reading asap. How does it do if you try another fuel source? Keep tank above 1/2 tank for now. Consider 1/2 tank as empty. I never allow tank to get below 1/4 full. You have to remember that fuel pump is cooled by fuel around it. Spray water around the top engine and intake area, while running, to see if rpm steadies or picks up if you find a vacuum leak. If you have a mechanic's stethoscope you can pull the probe out of the end and listen for it as well. Run some injector cleaner thru it since you could have a fuel feed problem caused by junk in the system from running tank too low. You may also have a problem with the wires if you did not install right or used aftermarket wires. You said OEM plugs and then just said wires. You could also have an intermittent problem with the coils. Check all connections and make sure there is not a spade pushed out of a connector that is making intermittent connection.

https://www.rockauto.com/en/moreinfo.php?pk=7188700&cc=3438501&jsn=2187

https://www.rockauto.com/en/moreinfo.php?pk=8445304&cc=3438501&jsn=2219

https://www.rockauto.com/en/moreinfo.php?pk=8101696&cc=3438501&jsn=2239

https://www.rockauto.com/en/moreinfo.php?pk=6309438&cc=3438501&jsn=2170

 

[OR VietVet]

With the a/c on, that is a load on the system. That can accentuate any current problem that is there. I have a Tech 2 but have never looked at fuel pressure. From what I can tell just by reading at different sites the Tech 2 can check components that work with the fuel pump and see if they are functioning properly but I am unsure of reading the actual fuel pressure. Someone will now. You can rent or borrow a gauge and just screw it on the fuel rail schrader and get the actual reading though. I would do it when the level in the tank is low and the a/c on. Trying to duplicate the problem and get the reading then. Then fill the tank to at least 1/2 tank and do it again. Also get a reading with no a/c on in both modes. Get a KOEO reading and also what it says after starting and then also see what it does when you shut the key off.

You would spray the water around where the injectors are plugged into the fuel rail area and around where the intake bolts to the top of the engine and any where there is lines around the top area. You may even get a misfire spark that jumps when the water hits it. Like even a bad new plug wire or coil.

I thought in your OP that you saw 3 misfires. That could be coil(s) but hopefully not. Maybe even coil connector problems.