Ls 400 Misfire

soundchaser100 · March 25, 2008

My 1996 UF20 has an intermittant misfire when the engine is warm. Most noticeable at tickover but i'm sure it misses at speed when the throttle is closed or at a low setting. This problem got a lot worse after I changed the spark plugs and cleaned the throttle body. The engine runs very smoothly but for the misfire every few seconds, sometimes it doesn't happen. When stopped at lights, the misfire will start after 30 - 40 seconds. Any help please?

steve2006 · March 26, 2008

Hi and welcome to LOC,

Did you also change the plug leads when you replaced the plugs? They generally get damaged by aging and the physical strain of being pulled off the plug tops and moved out of the way.

It may be worth looking under the bonnet in the dark when the fault is present and see if there is any tracking/arcing present.

Also were the plugs OEM spec, gapped correctly and tightened to the correct torque?

Cheers,

Steve

soundchaser100 · March 26, 2008

Hi and welcome to LOC,
Did you also change the plug leads when you replaced the plugs? They generally get damaged by aging and the physical strain of being pulled off the plug tops and moved out of the way.

It may be worth looking under the bonnet in the dark when the fault is present and see if there is any tracking/arcing present.

Also were the plugs OEM spec, gapped correctly and tightened to the correct torque?

Cheers,

Steve

soundchaser100 · March 26, 2008

Hi and welcome to LOC,
Did you also change the plug leads when you replaced the plugs? They generally get damaged by aging and the physical strain of being pulled off the plug tops and moved out of the way.

It may be worth looking under the bonnet in the dark when the fault is present and see if there is any tracking/arcing present.

Also were the plugs OEM spec, gapped correctly and tightened to the correct torque?

Cheers,

Steve

I have ordered new plug leads and distibutors from Rock Auto on the strength of what I read elsewhere in the forum. The plugs themselves? Well I bought them from Halfords as they were the ones they specified for the car . They are Bosch, copper cored I think. It looks like they aren't the right ones. Can you tell me which are the right ones for this model and the gap. When I fit the leads and dists I can fit the correct plugs. Thanks for your swift reply, look forward to learning loads about my lovely Lexus. Paul

Haylands · March 28, 2008

Hi and welcome....

Bosch copper core..... oh dear.

The original ones are Denso iridium plugs, they are very expensive and for a good reason, they last about 100,000 miles and work properly with a spark twice as powerful as a normal plug.

There are cheap things for a Lexus and there are good value things, use cheap and the car will suffer, but you don't have to pay dealer prices, there are many other outlets now for iridium plugs including lots on the american eBay site www.ebay.com (not .co.uk) they will send to the uk and for a reasonable price as well.

You have bought one of the best cars in the world but you have to use the right stuff to keep it that way so if in doubt ask on here first...

Good Luck

Pete

soundchaser100 · March 29, 2008

Hi and welcome....
Bosch copper core..... oh dear.

The original ones are Denso iridium plugs, they are very expensive and for a good reason, they last about 100,000 miles and work properly with a spark twice as powerful as a normal plug.

There are cheap things for a Lexus and there are good value things, use cheap and the car will suffer, but you don't have to pay dealer prices, there are many other outlets now for Iridium plugs including lots on the american ebay site www.ebay.com (not .co.uk) they will send to the uk and for a reasonable price as well.

You have bought one of the best cars in the world but you have to use the right stuff to keep it that way so if in doubt ask on here first...

Good Luck

Pete

Thank you, I will heed your wise words. Paul

soundchaser100 · April 21, 2008

Hi and welcome....
Bosch copper core..... oh dear.

The original ones are Denso iridium plugs, they are very expensive and for a good reason, they last about 100,000 miles and work properly with a spark twice as powerful as a normal plug.

There are cheap things for a Lexus and there are good value things, use cheap and the car will suffer, but you don't have to pay dealer prices, there are many other outlets now for Iridium plugs including lots on the american ebay site www.ebay.com (not .co.uk) they will send to the uk and for a reasonable price as well.

You have bought one of the best cars in the world but you have to use the right stuff to keep it that way so if in doubt ask on here first...

Good Luck

Pete

Thank you, I will heed your wise words. Paul

As an update, the new plugs and HT leads fixed the problems, it ticks over like a swiss watch now. Paul

Manc · June 18, 2008

Hey Heylands,

Bosch copper core.......oh dear!!!

that just made me laugh proper.....

But its made me want to check mine 'cos the last mechanic put the wrong transmission fluid in so i presume he's gone cheap with plugs too.............

See you around