compression and leakdown test how to?
- Thread starter NEWSVTGUY
- Start date
Compression test is real easy. While the engine is still warm, remove all the plugs. Insert the comp tester hose into the first cylinder and while holding the gas pedal to the floor crank the engine through at least 3 complete cycles (6 revolutions). Write down the result and repeat on the other 7 cylinders. You do need to bleed the air from the tester between cylinders.
A leakdown test will require an air compressor. To do it bring the cylinder you are testing to TDC of it's compression stroke. Insert the leakdown tester hose in the cylinder being tested and attach the compressed air source. A leak of more than 20% on a cold engine is cause for alarm. If more then 20% get a length of 1/4" to 1/2" tubing to use as a listening device. Put one end to your ear and probe the other end in the exhaust, throttle body, pcv valve hole and also adjacent cylinders. What you are dong is listening for the sound of escaping air to pinpoint where your cylinder leak is.
1. PCV hole = pistons or rings
2. Throttle body = intake valves
3. Exhaust = exhaust valves
4. Adjacent cylinders = head gasket and or valves.
note that a bad head gasket can simulate other locations.
A leakdown test will require an air compressor. To do it bring the cylinder you are testing to TDC of it's compression stroke. Insert the leakdown tester hose in the cylinder being tested and attach the compressed air source. A leak of more than 20% on a cold engine is cause for alarm. If more then 20% get a length of 1/4" to 1/2" tubing to use as a listening device. Put one end to your ear and probe the other end in the exhaust, throttle body, pcv valve hole and also adjacent cylinders. What you are dong is listening for the sound of escaping air to pinpoint where your cylinder leak is.
1. PCV hole = pistons or rings
2. Throttle body = intake valves
3. Exhaust = exhaust valves
4. Adjacent cylinders = head gasket and or valves.
note that a bad head gasket can simulate other locations.
+2 damn nice, very informative.
You don't want to start the car to do a comp test. All the plugs will be out of the engine so it can't possibly start anyway. You just crank the engine with the starter.
Have someone else turn the key while you hold the tester. You will know each time you hit a compression stroke.
for the comp test what is a good, ok, and bad reading?
It's not so much the reading as it is the consistency between the cylinders. You don't want to see a 20% difference between the lowest and highest cylinder. But the average Terminator, in a healthy cylinder, is about 155 psi. Try running the test and posting your results here.
Oh yeah and a cold motor will just result in a little lower readings. If you have a problem that's causing the engine not to even run, you would have to have 0 compression in several cylinders.
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