Misfire and headlight dimming

[okfoz]

2007 Tahoe LTZ, 4L60, 4x4, 311,000 miles.
A week ago I noticed upon hard acceleration that there was something amiss, I could feel the engine misfire. Then 2 days ago the engine would misfire pretty bad at a cold startup, but it went mostly away as it warmed up. I thought I got some bad gas, talked to a mechanic friend and he suggested resetting my Ethanol sensor, and sure enough it was reading high, this helped a little, but still getting random misfires.
I plugged in my tech 2 and it was misfiring occasionlly on 3-4-5-6-7 but mostly 7. I pulled the plug on 7, it looked fine, color was good, not oily, but the *** was missing on the plug which was only 50,000 miles old. I had an old plug that looked better, so I put that in, and it ran a little better.
What I noticed tonight was the headlights, and interior lights dim every time I get a misfire. Which seems odd to me.
Wondering if anyone has run into this, I thought maybe a bad ground, I have no SES light, no engine codes at all.
I am going to try replacing plugs and wires to see if it helps, but because the lights dim I am wondering if I sould look elsewhere too.

 

[petethepug]

Disconnect battery, slow charge overnight and have a shop load test it. Replace if needed. If not …

Time to replace your -/+ battery cables. They rot from inside out but still look perfect.

You also need to verify your fuel pressure off the tap on the fuel rail. If subpar only replace w/ OEM ac Delco - GM unit from R/A - about 2-$2.5h.

 

[okfoz]

I replaced spark plugs and wires 1-7, I can never do 8, so I pay someone to do it for me. I was not getting a misfire on 8, however if I continue to get a misfire I will be getting new battery cables, I appreciate the input on that. I have a friend who I asked about my issue and he said the exact same thing and there is a TSB on specifically the positive cable, and there should not be more than a .2v variance between the battery and. The where it connects to the starter.. So that will be next. Thank you for taking your time to reply.

 

[okfoz]

I ordered new Battery cables, hoping to do both of those this weekend.

 

[okfoz]

Update, I was able to replace cyl 8 plug and wire, and I replaced both the positive and negative cables at the same time. I did not mention this, but for starters my overnight draining of the battery has gone away, I am not sure how but it appears the battery cables were somehow not allowing the alternator to charge the battery. Ever since I put the new cables on, I have not had a dead battery even when letting it sit for a full 24 hours, which is way better than the 8 hours prior. Engine runs better too.

 

[Charlie207]

Disconnect battery, slow charge overnight and have a shop load test it. Replace if needed. If not …

Time to replace your -/+ battery cables. They rot from inside out but still look perfect.

You also need to verify your fuel pressure off the tap on the fuel rail. If subpar only replace w/ OEM ac Delco - GM unit from R/A - about 2-$2.5h.

Are there just two cables to replace? I don't remember off the top of my head.

 

[okfoz]

There are a couple more, but I just replaced the two that go to the battery. There is a large fuse on the firewall, and a large wire goes from that to the Fuse block on the Driver side. There is also a wire from the alternator that I did not change.

This is the Negative Cable I used:

Negative Battery Cable For 2007-2014 Chevrolet Tahoe/Suburban 1500 2500 22846471 | eBay

OE Number: 22846471 Feature: Durable and solid to ensure meet originally performance. Made of durable material, and have a long service time. It is a good replacement for the old or broken one. Easy installation, direct replacement. Vehicle Compatibility: for Cadillac Escalade 2007-2014 for...

www.ebay.com

When picking a negative cable, look closely where the cable attaches to the battery, most replacement cables are backwards, this one was correct for my 2007

This is the Positive Cable I used: GM

https://www.amazon.com/dp/B001DX9VVC?ref=ppx_yo2ov_dt_b_fed_asin_title

 

[swathdiver]

Update, I was able to replace cyl 8 plug and wire, and I replaced both the positive and negative cables at the same time. I did not mention this, but for starters my overnight draining of the battery has gone away, I am not sure how but it appears the battery cables were somehow not allowing the alternator to charge the battery. Ever since I put the new cables on, I have not had a dead battery even when letting it sit for a full 24 hours, which is way better than the 8 hours prior. Engine runs better too.

Misfires gone too? Is the alcohol content staying where it should?

How've ya been otherwise?