MngreLMatt

Howdy Everyone, 1999 LS 400
214,000k

Another obstacle on my path to become a decent DIY mechanic.

After changing out the original spark plugs on my '99 LS with NGK IFR6T11s something isn't quite right. When first turned over, the idle is sporatic around 1000-1200 cold start range. Once up to operating temperature it idles nice and smoothly around 650, except for about every 5 seconds there is a slight deeper sound and rumble. I'm not sure how to describe the sound really. From what I've searched it sounds as though it is a misfire. The sound isn't extremely loud or anything like that, it just isn't the same as the normal idle I'm used to. I cannot work on the car anymore today, although I would like to get this straightened out as soon as possible. Next thing on my mind to do is take all of the plugs out and make sure they are all gapped correctly. I do have a neat guy who is a Lexus specialist and charges fair prices who I want to take it into so he might be able to tell me exactly which cylinder the problem is happening in as to save many steps and failed attempts. Although I am very fond of the latter.
If you have anything you think might help or if you think I'm on the right path or even steer me in the right path I'd appreciate it.

After lots of searching I can only think of a couple of things that could be the culprit.

1. One or more of the plugs are not gapped to factory specs even though they were supposed to be pre gapped?
2. Maybe one or more of the plugs are faulty?

Thank you and pardon my ignorance; I am learning

Matt

Shmee

iTrader: (3)

You can narrow it down pretty quick. Pull the spark plug valley cover off and start the car.
Take a set of GROUNDED spark plug wire pullers and pop the leads off one by one. If a cylinder is working you will hear and feel and obvious miss when the leads is pulled.

If you do not notice a difference than you have likely located your problematic cylinder. Additionally, using the plyers, you can tea-bag the tip of the lead on and off the tip of the spark plug and listen/feel for any changes. You might find you just didn't have the lead on properly and the problem is resolved just by this.
If you find a problematic cylinder and the tea-bagging step shows no change pull that plug.

It's rare to have a faulty plug but infinitely more common for a plug to have a closed gap from mishandling or ham-fisted installs. And it is always a good practice to check your plug gap with the proper tool and adjust it with the proper tool as well. I have seen guys jam screwdrivers into the gap to open them up or tap them on the tip to close the gap... Both are bad ideas on normal plugs but are exceptionally detrimental on iridium tip plugs like the LS uses. Really easy to break a $15 plug doing either of those. A dropped plug is usually the most common cause of a closed gap, but if you are rough when putting the plugs down the tube or the plug drops out of your socket and you have to fish and force it back in to start threading it down, you can easily close the gap.


So for the TL;DNR folks, check that wires are on properly, pull plugs and check for closed gaps. You might want to pull all the plugs anyways and check just to be sure!

PureDrifter

iTrader: (10)

he's got a '99, so no high tension wires as it's coil on plug.

9/10 OP didn't connect one of the coilpacks properly or it isn't seated on the plug properly.

Or he bent one of the spark plug electrodes and it's just completing the circuit instead of shorting. (Been there done that, will look like this:
)

pull the plugs, check them all, reinstall properly, then recheck all the wiring and make sure you hear the connectors "click".

the plug gap as preset is almost always just fine. Modern precious metal plugs don't need adjustment for stock cars.

RA40

iTrader: (6)

Another chime for the dropped and bent plug scenario.

MngreLMatt

Shmee and PD you got it spot on. One of the plug's electrodes was bent. I must have bumped it in my excitement. Anyway with everything back in action the car idles at a perfect 650. This could also be in part due to the MAF cleaning I performed yesterday as well. It did not look dirty, although it was 15 years old so I'm sure there was something on there.

Weird thing is It used to idle at 400 at times. Kind of crazy, the old plugs were in pretty good shape for being 15 years old. Anyhow I'm sure the new plugs are doing a much better job and the low end acceleration feels smoother and slightly more giddy-up it feels like.

Here are the old plugs if anyone cares --https://www.clublexus.com/forums/ls4...other-day.html

Thanks again for all of the help.

I feel some intense shake when breaking so I'm sure the rotors are shot. The pads are also due for a change so looks like that is next on the list.

THIS WAS THE CULPRIT

PureDrifter

iTrader: (10)

Ahem.

Called it.

Shmee

iTrader: (3)

Of course you did, pumpkin!

PureDrifter

iTrader: (10)

i posted the picture. i win.

Unless you care to challenge me...

MngreLMatt

Which leads me to the question...has anyone found a thin walled spark plug socket with a grommet that actually fits in the tube? I have a couple with grommets from previous family cars although none of which fit in the opening of the tube. I was thinking of Jerry rigging a piece of electrical tape around the circumference of the socket opening to creat just enough friction to keep the spark plug in there while I lower it down the tube...I don't really know just spit-balling.

What do you guys do?

PureDrifter

iTrader: (10)

use my old craftsman spark plug socket that just happens to fit?

Shmee

iTrader: (3)

My snap-on spark plug socket works like a dream!


Challenge you? Pogs?

LScowboyLS

any reasonable quality spark plug socket, from Craftsman on up, will be thin-walled and fit just fine, probably at least 10 different brands, including all of the tool truck brands

PureDrifter

iTrader: (10)

at dawn then.

Shmee

iTrader: (3)

It's on like Donkey Kong!

steve2006

Get yourself a piece of flexible rubber pipe which fits snugly over the spark plug connector ( I used a piece of windshield washer pipe off my breaker),lower the plug into the hole and start the thread by twisting the pipe then pull off the pipe and torque up the plug.
Doing it this way also prevents possible cross threading of the plug during insertion.

If the plug drops out of the socket on removal use a magnetic probe to lift it out.