jbtvt

Working on my 98 LS400 but the Lexus forums aren't so tech savvy. It's been running like crap since last spring and giving me a random cylinder misfire code so I've had it parked. When pulling the water temp sensor to check it (fine) I noticed that the coolant looked clear, the red in the reservoir I was looking at was a stain. Thinking the PO might have filled it with water before I bought it, which I never checked, and then it froze and cracked something so I decided to do a leak test. Haven't checked the glycol content with the float measure yet though I intend to.

All numbers are cold because the starter also happened to seize, hopefully would even up some of the less extreme differences if it was warm. Air inlet at 90PSI. Odds are DS, evens are PS.
1- 87 PSI
2- 79
3- 88
4- 56
5- 79
6- 11
7- 76
8- 81

So my lowest cylinders 4 and 6 are right next to each other, but what I don't understand is that when I pressurize cyl 4 I hear air leaking out the plug hole for cyl 2 and nothing from cyl 6, and I hear air from cyl 6 leaking out cyl 8, whereas 2 and 8 don't have any apparent leaks themselves. I would've repeated the test to be sure I didn't mess anything up but was starving and had to come up and cook. Barring user error, anyone have any idea what might cause this?

millball

Are you testing each cylinder at its own TDC point??

jbtvt

Yes.
Edit to note that I also measured in the firing order of 1,8,4,3,6,5,7,2 so I would be measuring TDC compression for all, shouldn't have mixed TDC exhaust somehow.

millball

Then it sounds like you may have some leaky intake valves.

There's no telling what cylinder/cylinders might bleed air because one or more intake valves will always be found to be open when you have got another one under pressure at its own TDC point.

jbtvt

Good point, and it adds to your theory that the cylinder that was leaking in both cases was 5 ahead in firing order of the one being tested, which seems like it would be intake stroke. Not sure how this could've come on so suddenly and so severe like this, in two separate cylinders from intake valves though. I did the valve gasket on the other head to stop an oil leak from around the plug tube and checked clearances and all were dead on.

I'll redo the test tomorrow and if it comes up the same looks like I'll have to open this side too.