cause of low compression?

domi · 09-13-2002, 05:45 AM

what causes low compression(PSI)? I did a test on my car and got 115 115 115 105..

:

V-Technician · 09-13-2002, 05:51 AM

Could be a worn piston ring, head gasket leak, or even a bad spark plug, however the latter can be disregarded for obvious reasons.

B20BbenN · 09-13-2002, 03:49 PM

Always open the butterfly when you do a compression test!(bypass the + on the starter , not turn the key...)
If you open the butterfly during the compression will be higher!

taz77 · 09-14-2002, 09:11 AM

Quote:

Originally posted by B20BbenN
Always open the butterfly when you do a compression test!(bypass the + on the starter , not turn the key...)
If you open the butterfly during the compression will be higher!

i've heard you're supposed to have the throttle at wot, but i still don't get why. lets say the intake valve isn't seated properly and is having a low compression because or that. won't having the throttle closed help the compression because the throttle plate is allowing the air to stay in the cylinder/engine? just curious here...

but anywayz.. any of what they say can be a cause of low compression but there are more possibilities... are you burning any oil? are you loosing coolant? was a leak down test done after the compression test?

summitfan · 12-11-2005, 04:20 PM

what kinda car u got, one cause of low compression is u may have jumped timing. and when u do a compression test keep throttle wot and disconnect the ignition wire dont fuck wit the starter. if it was a head gasket leak u would hear it it it was rings it would smoke. could have burnt valves. good luck!

hobie237 · 12-11-2005, 05:12 PM

could be upper end or lower end. How many miles?

female four · 12-12-2005, 02:53 AM

Quote:

Originally Posted by taz77

i've heard you're supposed to have the throttle at wot, but i still don't get why. lets say the intake valve isn't seated properly and is having a low compression because or that. won't having the throttle closed help the compression because the throttle plate is allowing the air to stay in the cylinder/engine? just curious here...

but anywayz.. any of what they say can be a cause of low compression but there are more possibilities... are you burning any oil? are you loosing coolant? was a leak down test done after the compression test?

you want throttle plate open to allow air to enter the cylinder. Blocking it will not allow enough air to enter. The test measure how much pressure is in the cylinder for combustion. If you don't have enough air pressure in there, you won't get power from the combustion.

yellowrexsi · 12-12-2005, 07:53 AM

Quote:

Originally Posted by *****hnician

Could be a 3 year old thread.

:noo