sorka

SC400 272K miles. Test done warm with EFI fuse pulled. All measured between 232 and 242 PSI on a known good tester.

Piston tops are remarkably free of carbon build up. Chambers too. I stuck a fiber optic boroscope with a micro mirror down each cylinder.

These aren't normal numbers, right? If they're too high, then the only explanation is carbon build up or bad tester, right?

sorka

BTW, the car runs perfect. I was just testing it because of the high mileage and since I have the plugs out to change them while doing the timing belt, figured it would be worth the extra 15 minutes to do it.

tonyc9928

130-140 sounds rite for a motor with that miles. Usually 150-155 for a lower mile motor. Sure your reading the gauge correctly.

sorka

Well, thought about that but decided not to double, triple, or even quadruple check the way I was reading it

KC95SC400

iTrader: (3)

From the repair manual, 95.

12. CHECK CYLINDER COMPRESSION PRESSURE
(a) Reconnect the negative (-) terminal cable to the battery.
(b) Insert a compression gauge into the spark plug hole.
(c) Fully open the throttle.
(d) While cranking the engine, measure the compression
pressure.
HINT: Always use a fully charged battery to obtain engine
speed of 250 rpm or more.
(e) Repeat steps (b) through (d) for each cylinder.
NOTICE: This measurement must be done in as short a
time as possible.
Compression pressure:
1,226 kPa (12.5 kgf/cm2, 178 psi) or more
Minimum pressure:
981 kPa (10.0 kgf/cm2, 142 psi)
Difference between each cylinder:
98 kPa (1.0 kgf/cm2, 14 psi) or less
(f) If the cylinder compression in one or more cylinders is low,
pour a small amount of engine oil into the cylinder through the
spark plug hole and repeat steps (b) through (d) for cylinders
with low compression.
• If adding oil helps the compression, it is likely that the
piston rings and/or cylinder bore are worn or damaged.
• If pressure stays low, a valve may be sticking or seating
is improper, or there may be leakage past the gasket.
(g) Disconnect the negative (-) terminal cable from the battery.

Notice it says 178psi or more. Doesn't say anything about a max.

If the car runs good, I wouldn't worry about it since you didn't find any indications of a problem.

BTW, fluid of any kind in the chambers could cause a high reading but you would have seen it with the scope.

KC

cbrasian

sounds like you didn't do the test right possibly over cranked the motor normal number i've seen 145-175 but they should all be within 10% of each other

sorka

Mine were all within 4% of each other.

ConSynX

iTrader: (1)

the gauge essentially maxes out, so i dont think he overcranked.

There is the issue of started speed and it throwing off the numbers, SUPPOSEDLY...

a main question i'm having, are you reading the maximum number the gauge sees AT ALL, like during the crank, or are you using the number that the gauge settled at once you stopped cranking?

sorka

I'm not looking at the gauge during cranking. Also, I cranked for 5 seconds on each plug.

cbrasian

were those the numbers from the first time through or a subsequent one?
while its hooked up?

ConSynX

iTrader: (1)

maybe your engine is built
I had a friend w/ a Honda that maxed out my comp gauge...believe he was >13:1 CR...

i dunno what to tell ya.
that high w/o build up, and it sounds like you did it right, so :-\

sorka

There aren't too many errors that can cause a high reading. Plenty of error that can cause a low reading. Lowe battery, slow starter, not having the throttle body open, etc.

Again, the only possibilities are carbon or faulty gauge so one of those MUST be the cause. I have my money on the gauge being off even though it has been known to be good in the past.

The main thing I'm happy about is that the readings are so close together.

sorka

Revisiting this, I found this post:
http://us.lexusownersclub.com/forums...howtopic=20176

Where this owner got the sam results I did.

mdmaniac

Maybe someone popped a head gasket on it? Didn't buy OEM or even meant to get the size they did. If the car runs good, don't sweat the details.

sorka

Um, no. A blown head gasket would not cause high compression results.