I put it off much too long, but today I finally did my spark plugs. I used NGK TR55 gapped at .050.

Lessons learned: The driver's side is simple
The only plug that makes sense to do from underneath is the rearmost one on the passenger side. The front three on the passenger side only are accessible properly when the AIR tube (I think) is removed. The second plug from the rear on the passenger side is the true challenge, took me almost 40 minutes and a lot of swearing.

2:20h, a dozen scrapes on the back of my hands and a car that feels totally transformed , not too bad for a first-timer I guess.

Seriously, the difference is huge, especially at low rpm. Next time I'm not gonna wait that long. I found that every plug I pulled had a gap bigger than .070...

Chris

 

I just did my passenger side plugs. Drivers side tomorrow. I had a horrible time getting #2 in. Took me about 1.5 hrs to get it in lol. 4 and 6 were stupid easy. I got them from the top. 8 was a real pain. I wrapped my arm around the y pipe and worked around an O2 sensor. Real pain to get out since the previous owner must not have antisiezed it. It was tight all the way out...

 

Mine were the stock GM plugs, but apparently GM doesn't use anti-seize either. Some of the plugs were very hard to break loose #6 was the worst and coincidentally the last one I did after finding out I could not get it from underneath.

But the result was worth it

 

The ones I took out were Bosh plugs with 4 little prongs(dont know what theyre called) instead of the usual one. They all looked good but one of them was corroded like crazy where the boot goes onto it.

 

How long did it take you? First time every changing plugs was this car and took me two days? I found that the routing of the wires was even more of a pain to get it right.

 

Definitely sounds like you needed plugs. The pucks fell off of your platinum plugs most likely causing those excessive gaps. When I did the plugs on my car, the gaps were in the .080 range. I'm very surprised the car ran at all.

 

It took me 2 hours 20 minutes. My car is a LS1 and the wire routing is pretty much straightforward. I heard that it's a different matter on LT1 cars though...

 

Interestingly the tiny platinum pucks still were there (much smaller than the center electrode on the TR55s), just on all plugs the little hook was farther 'up' than it was supposed to be. The gaps on the old plugs were almost dead even between .070 and .075. The new plugs were at .060 when I bought them and I gapped them at .050 as recommended in the shop manual.

The difference in driveability and power is indeed huge, although interestingly I did not get a code for misfire.

My recommendation to every LS1 owner who experiences a drop in mileage and performance, check your spark plugs. It's easy enough to pull one or two plugs on the driver's side and if they look bad, change the whole bunch.

Before:
Now: