After reading on this forum that Lexus changed the recommendation for spark plugs for the LS400 from PK20R8 to PK20R11, i was confused. For years and years my LS400 1996 produced 05/1996 was slow, drank a lot of gas, bad throttle response. I had brand new PK20R11 plugs and suffered with them for 100,000 miles and had no idea this was the root of my problems. PK20R8 was written in the original owners manual I believe. If you look at the online manuals and the free replacements they mail out, it says PK20R11 and not PK20R8 as originally.

I went with the PK20R8 which I heard was meant for Aug 1996 production LS400 and earlier and WOW. As the person who posted about it earlier says, it feels like the inner beast has been unleashed. It actually feels like I have a V8 now! I haven't checked yet officially but can already tell the mpg will also improve.

If anyone out there has a 1996 or maybe 1997 LS400 that is kinda sluggish to pick up and you are listening to the Lexus/Toyota dealer or online official website recommendations, forget it. Go with PK20R8 which is a smaller gap. I would have paid a lot of money for this advice years ago!

Something inside me feels this was a measure to make one recommendation to everyone to make their own life easier or a way to sabotage a perfectly running car that might run forever lol. Now I know why so many many many LS400 have the catalytic converter codes, they were getting fouled up.

PK20R8 >>>>>>>>>>>>>>> PK20R11

 

The Irridium tips are pretty easy for a good ignition system to spark and that applies even with platinum and copper (in the day).

The listed spec on the:
PK20R8 is .032"/.8mm
PK20R11 is 044"/1.1mm
I have the NGK BKR6EIX .044"/1.1mm in ours.

Glad it works well. Did you change the ignition wires and caps, rotors too?

 

sounds like symptoms associated more with a bad coolant temp sensor than spark plugs to me.

 

Me too.. Ignition wires were changed 100,000 miles ago didnt bother yet.. Caps and rotors waiting for the upcoming timing belt change since that makes them accessible.

 

Yes I thought so too.. I changed that a few years ago with no good results. Quite happy now, that throwback in my seat feels great as subtle as it is

 

Interesting.....

 

Well another amazing update.. First time in 8 years of ownership I got 18 mpg in the city driving and pushing it hard all around, I'm quite shocked, was always envious of other owners on here getting good gas mileage.. I never got more than 13/14 in the city and that too by driving like an egg was under the accelerator. Otherwise was getting around 10-12 average in the city. 8 years of suffering and changing parts and computer diagnostic waves showing everything was fine and the only issue was a TINY gap change in a plug, unbelievable. Owe it to these forums whoever brought this up before otherwise this beast was about to his the pasture.

I highly highly recommend using PK20R8 instead of PKR2011 if you get bad mileage and your car feels like a 4 cylinder!

 

Sounds like using the smaller gap is compensating for a weak spark?Awesome that it has worked out so well for you!

 

No shortage of power in my 99 but what spark plugs do ya recommend for my 99?

 

What would be the cause of a weak spark? Wires, caps, rotors?

 

I'm not sure, I think you are good to go with the current factory recommendation for the 99, the iridium ones SK20R11

 

I cant speak specifically to LS,I havent touched my ignition yet.But all three,with corrosion and spread gaps are not good for transferring that current to plugs.

For example,my 1967 jeep.A spark so weak you could barely see or hear it.In Bad weather,any fog,rain,cold,didnt want to start.Put on electronic ignition,nice modern new wires,rotor,cap,plugs and a 50,000 volt coil and it shoots a massive spark that that goes CLACK with each spark.My issues are all gone now.

So all you mention,plus coil(s) if weak,I would replace if the other stuff didnt fix it,BUT defer to the LS experts when they chime in.I could be all wet here,but I dont think so.

My philosophy on old cars is if a system has an issue on an old car,I replace the whole system if within reasonable costs I can handle.

 

There may be a way to increase the voltage without changing the ignition coil for your 1967 Jeep just optimizing the dwell angle, spuds.

People wonder why the spark plug gap for post Aug 96 was changed from 0.8mm to 1.1mm although ignition coils, ignitors and spark plug cables were not changed at all. The wider spark plug gap requires higher voltage. How can it be possible without changing those major key parts?

The reason why the gap is increased is to have better igniting capability to meet the newer and stricter emission control. But without changing those 3 major parts, how Toyota succeeded to increase the voltage?

The answer is the increased dwell angle or the driving timespan of the ignition coils controlled by the ECU. The longer drive time makes it possible to increase the voltage if the ignition system is OK to do so. Optimizing the ignition control software, Toyota made it possible to get the higher voltage. This is rather too technical but the detail of this method can be find at the page 13 of this site. The increased driving timespan increases the accumulated energy to the coil and this makes the voltage higher if the ignition coil is capable. The original one 90919-02197 was OK to do so and the change was done only by the newer software and spark plugs.

 

Smartest answer I ever heard, thanks for the education and providing your in depth knowledge of such an issue.