Low compression numbers?

[nissanrcer240]

We did a compression test today on my motor, and Im definetly not happy with the numbers, here they are:

1-1302-1303-1304-105

I've heard of other peoples motors being like 150 all the way across, what would cause the mine to be so low, especially in number 4? The car runs strong as ever. The only problem Im having now is that Im not getting enough vacuum pressure to make the BOV functional from the big nipple above the throttle body, I had to hook it up to the little one on top of the throttle body. When I hook the boost gauge up to the little one it reads between 19-20 while in vacuum while it idles, but when I hook it up to the big one it reads at 10 vacuum while its idleing. Would the low compression have anything to do with this?

[The Mic]

I would reccomend performing a leak down test, this will help to lacolize the problem. If you hear air leaking out the intake, its your intake valves, if its coming out your exhaust, its your exhaust valves, dip stick tube then its your rings, etc.

The most important thing is that they are all similar pressure ratings..

as in, you wouldnt want1 at 1902 at 1953 at 1204 at 190

[nissanrcer240]

How do you perform a leakdown test? Whats needed?

[The Mic]

The test involves a special gauge and adding compressed air to measure the percentage of leak in the cylinder. One face of the gauge measures the pressure of the compressed air that you are forcing into the cylinder, and the other face measures the percentage of this pressure that is being lost. There is a knob on the gauge that lets you control the pressure going in so you get even results.

There are many manufacturers of these gauges and they are available at just about any auto parts house. Depending on the particular “Leak Down” test gauges you get, the actual test will go something like this:

1. Take out the spark plugs. 2. Bring each cylinder to TDC (top dead center) so that all it’s valves are closed. 3. Screw the gauge adapter into the spark plug well and connect the gauge. The gauge has a fitting to connect the extender hose to the spark plug well, and another to connect the air hose. 4. Apply the compressed air and modulate the knob to get a steady reading from both faces on the gauge. Use the same pressure on all cylinders. 5. LISTEN to where you can hear the compressed air. At the crankcase: Remove the oil filler cap. If you can clearly hear a whooshing/howling by listening at the oil filler cap, you're losing compression through the rings. At the tailpipe: It is your exhaust valves if you can hear it (or even feel puffs on your hand) at the tail pipe. At the intake manifold: It is your intake valves if you can clearly hear a whooshing/howling by listening at the throttle body/intake manifold. 6. Repeat steps for each cylinder.

If the results are inconclusive, it could be a blown head gasket. Symptoms of a blown head gasket are: reduced power, white or blue smoke out the tailpipe, oil in the coolant or coolant in the oil. You can check for a blown head gasket by removing the coolant cap and watching the coolant level when you add the compressed air. If it rises or you see bubbles, you have a leaking head gasket.

[kane2g]

The test involves a special gauge and adding compressed air to measure the percentage of leak in the cylinder. One face of the gauge measures the pressure of the compressed air that you are forcing into the cylinder, and the other face measures the percentage of this pressure that is being lost. There is a knob on the gauge that lets you control the pressure going in so you get even results.

There are many manufacturers of these gauges and they are available at just about any auto parts house. Depending on the particular “Leak Down” test gauges you get, the actual test will go something like this:

1. Take out the spark plugs. 2. Bring each cylinder to TDC (top dead center) so that all it’s valves are closed. 3. Screw the gauge adapter into the spark plug well and connect the gauge. The gauge has a fitting to connect the extender hose to the spark plug well, and another to connect the air hose. 4. Apply the compressed air and modulate the knob to get a steady reading from both faces on the gauge. Use the same pressure on all cylinders. 5. LISTEN to where you can hear the compressed air. At the crankcase: Remove the oil filler cap. If you can clearly hear a whooshing/howling by listening at the oil filler cap, you're losing compression through the rings. At the tailpipe: It is your exhaust valves if you can hear it (or even feel puffs on your hand) at the tail pipe. At the intake manifold: It is your intake valves if you can clearly hear a whooshing/howling by listening at the throttle body/intake manifold. 6. Repeat steps for each cylinder.

If the results are inconclusive, it could be a blown head gasket. Symptoms of a blown head gasket are: reduced power, white or blue smoke out the tailpipe, oil in the coolant or coolant in the oil. You can check for a blown head gasket by removing the coolant cap and watching the coolant level when you add the compressed air. If it rises or you see bubbles, you have a leaking head gasket.

Thats probably the most informative explanation of a leakdown test I have read on any forums.If I had a cookie, I'd give it to ya, but I don'tAll I can hope is that some MOD will add this to FAQ.Good job man

[The Mic]

well you can email one of the administrators/moderators to have my post nominated for FAQ status. though, with my name on it, the chances of that happening look slim. So save it on word!

[nissanrcer240]

The test involves a special gauge and adding compressed air to measure the percentage of leak in the cylinder. One face of the gauge measures the pressure of the compressed air that you are forcing into the cylinder, and the other face measures the percentage of this pressure that is being lost. There is a knob on the gauge that lets you control the pressure going in so you get even results.

There are many manufacturers of these gauges and they are available at just about any auto parts house. Depending on the particular “Leak Down” test gauges you get, the actual test will go something like this:

1. Take out the spark plugs. 2. Bring each cylinder to TDC (top dead center) so that all it’s valves are closed. 3. Screw the gauge adapter into the spark plug well and connect the gauge. The gauge has a fitting to connect the extender hose to the spark plug well, and another to connect the air hose. 4. Apply the compressed air and modulate the knob to get a steady reading from both faces on the gauge. Use the same pressure on all cylinders. 5. LISTEN to where you can hear the compressed air. At the crankcase: Remove the oil filler cap. If you can clearly hear a whooshing/howling by listening at the oil filler cap, you're losing compression through the rings. At the tailpipe: It is your exhaust valves if you can hear it (or even feel puffs on your hand) at the tail pipe. At the intake manifold: It is your intake valves if you can clearly hear a whooshing/howling by listening at the throttle body/intake manifold. 6. Repeat steps for each cylinder.

If the results are inconclusive, it could be a blown head gasket. Symptoms of a blown head gasket are: reduced power, white or blue smoke out the tailpipe, oil in the coolant or coolant in the oil. You can check for a blown head gasket by removing the coolant cap and watching the coolant level when you add the compressed air. If it rises or you see bubbles, you have a leaking head gasket.

Thanks alot for the detailed response, it will definetly come in useful when I attempt the leakdown test. I appreciate it