Low compression? why?
11-08-2008, 11:39 AM
#1
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Low compression? why?
I did a compression test last week and my numbers never went above 110 at times hit 30 as the lowest. I made a graph if it helps anyone. my question is why so low. everything runs fine I was just checking everything out. my oil gets a little low with no leaks.
But Im guessing I should have more power. and it is completely stock with an after market intake and muffler nothing special.
But Im guessing I should have more power. and it is completely stock with an after market intake and muffler nothing special.
11-08-2008, 12:04 PM
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Re: Low compression? why? (lluks_844)
Yea I did the following steps
1. took spark plugs out
2. took f/i fuse out
3. disconnected distributor
4. connected tester in the spark plug hole
5. held throttle wide open as my friend kicked the engine over.
6. wrote down the info. repeated 7 times per chamber starting with #1-#4
could it be the amount of carbon deposit.
graph:
1st time
#1- 100,100,70,75,80,80,70
#2- 25/105,105,105,105,100,105
#3- 30,105,105,105,80,80,80
#4- 105,85,105,105,105,105,75
2nd time
#1- 35,105,90,90,75,95,105
#2- 30,110,105,105,105,90,100
#3- 105,80,105,105,85,80,80
#4- 110,105,110,105,110,110,105
after I did the test I tried a steam cleaning trick I seen before by mixing alcohol and hot water and spraying it in the brake booster hose down to the intake and hold the rpm's at 3000 but got scared and stopped. then took the spark plug out and looked in the combustion chamber and noticed that there was alot of broken carbon deposits in the chamber.
1. took spark plugs out
2. took f/i fuse out
3. disconnected distributor
4. connected tester in the spark plug hole
5. held throttle wide open as my friend kicked the engine over.
6. wrote down the info. repeated 7 times per chamber starting with #1-#4
could it be the amount of carbon deposit.
graph:
1st time
#1- 100,100,70,75,80,80,70
#2- 25/105,105,105,105,100,105
#3- 30,105,105,105,80,80,80
#4- 105,85,105,105,105,105,75
2nd time
#1- 35,105,90,90,75,95,105
#2- 30,110,105,105,105,90,100
#3- 105,80,105,105,85,80,80
#4- 110,105,110,105,110,110,105
after I did the test I tried a steam cleaning trick I seen before by mixing alcohol and hot water and spraying it in the brake booster hose down to the intake and hold the rpm's at 3000 but got scared and stopped. then took the spark plug out and looked in the combustion chamber and noticed that there was alot of broken carbon deposits in the chamber.
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11-08-2008, 04:53 PM
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3. disconnected distributor??????? ummm, I didnt do that.
and.. you aren't cranking it once , checking the gauge, cranking it again, checking the gauge, etc etc are you?
crank it five times, then check it. that's it, next cylinder.
and.. you aren't cranking it once , checking the gauge, cranking it again, checking the gauge, etc etc are you?
crank it five times, then check it. that's it, next cylinder.
11-08-2008, 05:49 PM
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^^^This man speaks the truth..
and IMHO any reading under 125psi is rebuild time.
..and why would your readings be low you ask?...worn rings,poor maintenance,excessive valve to seat clearance are just a small list of what could be.
and IMHO any reading under 125psi is rebuild time.
..and why would your readings be low you ask?...worn rings,poor maintenance,excessive valve to seat clearance are just a small list of what could be.
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11-16-2008, 05:40 AM
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There ya go.
Most people think you only crank it to one compression stroke and that's it. Also, just as a side note, carbon buildup on the tops of the pistons will increase compression, but if you've got carbon buildup on the valve seats it will reduce compression due to the valve not seating properly.
I seriously think that there needs to be a sticky on the first page for a compression test as these threads pop up every day.
Most people think you only crank it to one compression stroke and that's it. Also, just as a side note, carbon buildup on the tops of the pistons will increase compression, but if you've got carbon buildup on the valve seats it will reduce compression due to the valve not seating properly.
I seriously think that there needs to be a sticky on the first page for a compression test as these threads pop up every day.
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