compression test help

[cj062989]

so im no expert so thats why im askin, when doina a compression test do i reinstall the spark plug in the cylinder i just got done with or can i leave it out and should i do it at WOT or do i just do it with throttle closed?????

 

[Vladimir]

i alway remove all spark plugs and do it. i never open the throttle plate or anything. As long as all the cylinder are in 10 percent of each other you should be good, that is if all of them are not low.

 

[guapking]

You can remove all plugs when you do it. You leave the throttle closed just crank the engine and get your reading.

 

[cj062989]

Once again thanks it amazing how quick and responsive the people on this site are appreciate it guys.....

 

[goldbomb79]

Also unplug the coil pack and injector wires. You don't want to pump a bunch of fuel in the cylinders when it's not running.

 

[goldeninja20]

i always like to floor it (open throttle all the way). This way the cylinders do not have any trouble getting air to build the compression. You will get much lower readings with the throttle plate closed. Do take out all the spark plugs and unplug injectors.

 

[cl1ckclack]

ive been told by a few different people that your supposed to remove all spark plugs, unplug injectors, open the throttle completely, and crank it over 5 times.

 

[cj062989]

well the results are in cylinder 1-160, 2-168,3-170,4-125...... opinions please


i went out side and put only a cap of SAE 30 oil in the cylinder and it went up to 180, so im thinking it definitely the piston rings that went and not a valve... am i right?????

 

[Vladimir]

If you add oil to the cylinder you seal up the rings, so yea it's the rings. But make sur that that cylinder doesn't get washed out with fuel. Sometime compression will drop if your injector is stuck open and it washes out all the oil from the rings lowering the compression (very rare) but it's worth to check it out.

Shine a light through the spark plug hole and compare the piston condition to the other 3, look for wet and a lot cleaner surface than the other cylinders, also look at the condition of the spark plug, if it's wet and smells like fuel.

Also if the rings are bad and the compression is low, you should see some blue smoke coming out of you exhaust on acceleration, the heavier you accelerate the more blue smoke you get.

Just a thought.

 

[cj062989]

Vladimir, thanks for the useful info.. out of no where while underboost in 2nd gear the car just stalled but prior to failing on me the car was running AMAZING... that motor even spun a bearing and i change it 4000 miles a go and not even a single knock appeared. i sure as hell thought that knock would have gotten me but not low compression...