Impossibly high compression results????????
#1
Lead Lap
Thread Starter
Impossibly high compression results????????
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?
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?
#2
Lead Lap
Thread Starter
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.
#5
Lexus Test Driver
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
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
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#8
Lexus Test Driver
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?
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?
#12
Lead Lap
Thread Starter
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.
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.