I have a 1990 LS 400 with 92,000.00 miles on her, and I have done everything and I do mean everything and since I am 64 years old and this is my first time doing anything on this car since new I will tell you that you MUST use anti-seize on the plug threads, and ALL plugs are worn at 100,000.0 miles the car just does not know this but your mileage and power will increase after you do the repairs.Also consider the plug wires if your car has them.One more thing-Use only the plugs that the book calls for.I put the best plugs in my car and had 2 go bad in less then 500 miles so I replaced with denso as called for in the book and no more problems.About my LS400 I have #623 and think that It could be the oldest LS on the road, she is like the day I purchased her and to date have never had a brake down.I do all my own repairs,but I am thinking about a new LS and do not need 2 cars so maybe a sale is in the works.Also when I ordered this car in 89 I purchased 16 inch 3 piece wheels and had to have lexus do the upgrade to keep the warranty so I do not have the old 15 inch but I still have the spare and it still is holding air after 24 years and I have never used it or the tool kit-first aid kit or tire jack.I really injoy driving my LS to the movies on saturdays but do not use her more then that. I drive my motor cycle.THIS car is like new and will last for many years to come PS has lexus phone-stereo but no track ride system ,thank god

 

Changed my spark plugs today on my LS430. Out: Denso Iridiums. In: NGK Laser Iridiums. Process was fairly straight forward, key was taking my time and being as gentle as I could with the wire connectors going into the top of the coil packs when removing them. Hand tightening the new plugs to avoid cross threading until they were meeting resistance with the crush washers and then tightening a 1/4 to 1/2 turn to snug them down. The Denso plugs I took out were factory original to the car with 124k miles. They looked pretty darn good considering they had been in the engine 12 years. Probably could have gone another 25k but glad I replaced them. Took me about 2.5 hrs but could probably do it again under that time having now done it once. Best part: Turning the key after finishing with no codes and the engine sounding great. Thanks to all in this forum for the tips on how to do it. Great resource!!

 

GRAND_LS 4, when you changed the plugs in your 2002 GS430, did you have to remove a lot of extra items in the engine compartment to remove the plug connector? Such as the battery, power steering fluid container?

Thanks in advance,

Mike

 

I just changed all 8 of my plugs using OEM equivalent NGK.
The spark plug OEM is Denso SK20R11.
I removed all the engine covers and air filter duct.
I was able to get to every spark plug using a two different length extensions. I even used two small extensions attached together to allow room for the torque wrench when tightening to 13 ft-lbs.
I think it is important to use a torque wrench to make sure each spark plug is seated close to the same depth.
I am going to buy the drive locking extensions or maybe this one:

BE CAREFUL WHEN REMOVING THE 4 WIRE FEMALE WIRE HARNESS off of each end of the plug boot. I pulled all 4 wires out one of the ends. I used a large flat head screw drive to help pry the connections apart.


Also I checked the gap on each of the new spark plugs, which were pre-gapped, and all were consistently 0.040". The gap on one of the old spark plugs was about 0.044".

 

Wobble extensions for your ratchet make this job much easier.

 

I used a very small dab of anti-seize on the threads before installing the plugs. I don't care what the plug mfgs say the torque wrench tells me when to stop.

 

I don't know why you would want to skip the anti seize.

I have heard if youre not careful and get the anti seize near the tip, it can screw with the plugs. maybe that is why lexus does not recommend it? if youre worried about them coming loose, just drive a couple hundred miles and re-check.

also have to remember the head is aluminum, and the threads on the plug are not. seizing can become an issue here if you choose to skip anti seize. less is more when working with anti seize, you only need a small amount per plug.