Spark Plug Replacement LS400

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Sep 18, 2002
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My LS400 has started idling a little rough. No codes. So I decided to inspect the spark plugs. They have 85K on them. They were sooty and had a gap of 1.10.

That seems like a huge gap. I only checked 3.

They are Denso K20R11's

These need to be replaced, right?
 
I am surprised that the gap is more than twice what it was at install.

I am gonna replace them. Owners manual says e very 120K
 
Several of my original pugs had no-none-zero central electrode left at 75,000 miles. Chevy LS3 V8. Car ran fine though
 
The 11 at the end of the spark plug part number means 1.1 mm gap in Densos numbering system, so basically no gap erosion at this point, edit to say that I am assuming your gap measurement is in metric.
 
The 11 at the end of the spark plug part number means 1.1 mm gap in Densos numbering system, so basically no gap erosion at this point, edit to say that I am assuming your gap measurement is in metric.
You are correct. I was incorrect.
 
Sure are sooty. Look like an oil furnace flue.
 
Replace them. Check the PCV system as well.

These are out of my LS400 - 90,216 miles; original, factory installed. The ones on the right came out of the bank with the PCV valve. Don't rely on valve rattle to determine if it's working properly.
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I was mildly surprised that NGK's were in there. I purchased the car in '08 when it had 36k miles. I highly doubt that the dealership would have changed the plugs. Denso 3297's went back in.
 
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I have a new OEM PCV with only 1000 miles. One thing I did do was add a bottle of that Amsoil PI today and filled up my tank. Drove about 30 miles. Could that have something to do with the black soot on the plugs?

Blue Driver shows no pending codes.

Ordered Denso plugs on line from Advance Auto. Said they would be ready for pick up in 30 minutes. Drove across town only to find out they were closed. LOL
 
They should be PK20R11 :unsure:

Toyota says to replace them every 60k.

If the job is difficult, consider the iridium Denso SK20R11, or perhaps even the iridium TT. Either should last 100-120k
 
Just never try to clean the airflow meter on the older LS400's that will ruing them, if I remember right they have a small mirror in them?
 
Just never try to clean the airflow meter on the older LS400's that will ruing them, if I remember right they have a small mirror in them?
Did not know that. I’ve been using mass air flow sensor cleaner for many years.
 
Finally got the plugs changed. The carbon was gone. I don't know what I was thinking. I went back and reread my 1998 owner's manual and it clearly says to replace these plugs at 60K. What a knucklehead??? My baby runs like a Swiss sewing machine. I am so happy.

At least this had me go through all my other manuals and much to my surprise my 4Runner has 30K plugs. Not 100K plugs!!!
I replaced those today at 50K and it runs almost as good as the LS400. LOL!!!
 
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