Cylinder #3 misfire with AC on

I am having cylinder misfire at the #3 cylinder. Weird part about it is, it only happens when I turn the AC on full blast. When I don't have the AC on I dont have the misfire. I turn the AC on to low speed, I dont have a misfire. I turn the AC onto its highest setting, I have a very hard, pronounced misfire! Its a very noticeable misfire and shakes the truck! I got a log of it so you all could see it. I checked all my spark plugs wires thinking one came loose but nope, it still does it. Any suggestions? I believe this issue is going to be mechanical right? Probably a spark plug? How do I know which cylinder is #3 from looking at the engine?

Spark plug was fine no obvious reason for the misfire. That rules out the spark plug and the spark plug wire. What should I check next?

Fuel injector . . . bad impedance, possibly high. Find its stock value and then measure yours with a multimeter. I recently had one at 68 ohms rather than the spec value of 12 ohms that only caused a misfire while cold.

Rick

I believe you replied to my thread on performancetrucks.net, I posted here as well too see if I could get some different insights. I replied to your post and let you know that the injectors aren't stock. They are lt4 injectors bought new and installed 2 weeks ago. I will try this though. To measure the impedence do I have to remove the intake manifold?

I can't speak for a 2018 truck motor but for me, no need to remove the intake manifold. It would not be the first time that a brand new fuel injector failed soon after installation.

Rick

I'm going to try switching the spark plug to a different bank and see if it follows, then I'm gunna do the same thing with the injector on cylinder 3. See if it follows. I'll let yall know my results

Was told by a reputable shop that the plugs I am using are too cold and are causing the issues. They had the same issues with my current plugs. I tend to agree with them and am going to replace all of them to a hotter spark plug. Will update when done.

Spark plugs have been changed. Fingers crossed no more misfire.

The new spark plugs fixed it for a while and the misfire came back. I guess I'm going to buy stock spark plugs and see what that does. If it still misfires after that I am going to pull the lt4 injectors and get them tested.

Problem solved. Was a bad spark plug wire from Taylor racing. Hopefully they will warranty it or ill just go with msd.

I had similar issue at idle , find out some of spark plugs wires were loose.
I really don't know how I missed it out .