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Unread 05-02-2013, 05:22 PM   #1
Candymancan
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Are these compression numbers on my 5.9 ok ?

I havent ran a compression check in 2 years and the first time i did it wrong i didnt step on the throttle to open the valve body up..

So per what a few said to do since i fixed my intake manifold i did another compression check.. Engine was hot, Took all the plugs out disconnected the ignition coil and ran the check with throttle open all the way and checked with oil as well.. I should note i forgot to unplug the fuel pump so i think 1-3-5-7 are a tad lower then the other side because they were washed with gas


Here are the numbers first number is dry second is oil.

#2. 173-175
#4. 185-188
#6. 185-188
#8. 185-186

#1. 175-175
#3. 175-179
#5. 179-180
#7. 170-173.


They are all within 10% of eachother (well the 185's and 170's are close) and they dont really go up with oil in them.. But the compression just seems really high.. Perhaps my engine is really gummed up ?? or my engine is in very good health... or both lol. I dont know what the norm is suppose to be

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Unread 05-02-2013, 06:10 PM   #2
StrateLOSS
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compression tests are accurate it showing compression psi relative to the cylinder next to it.

meaning the "185" number may or may not really be 185, it could be 160 with a different gauge or 200 with another gauge.

everything is close enough that I'd be happy with those results.


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Unread 05-02-2013, 09:20 PM   #3
MN59ZJ
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Quote:
Originally Posted by StrateLOSS
compression tests are accurate it showing compression psi relative to the cylinder next to it.

meaning the "185" number may or may not really be 185, it could be 160 with a different gauge or 200 with another gauge.

everything is close enough that I'd be happy with those results.

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What??? If you zero out the gauge for each cylinder check, you should be looking at the exact number for each cylinder.

Quote:
Originally Posted by Candymancan

Here are the numbers first number is dry second is oil.

#2. 173-175
#4. 185-188
#6. 185-188
#8. 185-186

#1. 175-175
#3. 175-179
#5. 179-180
#7. 170-173.

They are all within 10% of eachother (well the 185's and 170's are close) and they dont really go up with oil in them.. But the compression just seems really high.. Perhaps my engine is really gummed up ?? or my engine is in very good health... or both lol. I dont know what the norm is suppose to be

Cylinder pressure should be between 120-150PSI with no more than a 20% variation of each other. Your's are high which may indicate carbon deposits in the cylinders.
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Unread 05-02-2013, 10:24 PM   #4
StrateLOSS
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Quote:
Originally Posted by MN59ZJ View Post
What??? If you zero out the gauge for each cylinder check, you should be looking at the exact number for each cylinder.




Cylinder pressure should be between 120-150PSI with no more than a 20% variation of each other. Your's are high which may indicate carbon deposits in the cylinders.
ok? what's your point ?


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Unread 05-02-2013, 11:52 PM   #5
Candymancan
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Quote:
Originally Posted by MN59ZJ View Post
What??? If you zero out the gauge for each cylinder check, you should be looking at the exact number for each cylinder.




Cylinder pressure should be between 120-150PSI with no more than a 20% variation of each other. Your's are high which may indicate carbon deposits in the cylinders.
120-150 are you sure about that ? I've seen alot of 5.9's on google with higher compression then that.. 120 seems really low like rebuild time low.

I know mine are high and i probly do have carbon specially since ive been burning oil for a long time and just finished my plenum.. but still
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Unread 05-03-2013, 12:36 AM   #6
jnicewan
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Yep the spec is 120-150 PSI. And that is measured with engine a normal operating temp. Most of the time the pressure specs would measure lower with colder engine temps.

I would say your guage is either inaccurate or you have carbon build up or something else causing elevated readings
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Unread 05-03-2013, 12:39 AM   #7
Candymancan
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probly carbon. when i saw my intake valves they were pretty nasty.. my engine still pings even after the intake was fixed and i have a catch can.. gauge is $30 gauge by actron .. probly not the best either but still.

soo what should i do then ? what will the higher compression do to the engine ?
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Unread 05-03-2013, 12:53 AM   #8
jnicewan
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Yea, its probably not the guage, its not usual for a guage to be inaccurate on the high side. Higher than normal compression is probably not going to hurt anything unless the engine is pinging a lot. The spark knock itself can cause damage. Since its pretty cheap and easy I would attempt to de-carbon the engine, maybe even double up on the cleaning.
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Unread 05-03-2013, 01:03 AM   #9
MN59ZJ
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Quote:
Originally Posted by StrateLOSS

ok? what's your point ?

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That the advice you gave is only true if you are doing the check wrong.
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Unread 05-03-2013, 01:06 AM   #10
MN59ZJ
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Quote:
Originally Posted by Candymancan

120-150 are you sure about that ? I've seen alot of 5.9's on google with higher compression then that.. 120 seems really low like rebuild time low.

I know mine are high and i probly do have carbon specially since ive been burning oil for a long time and just finished my plenum.. but still
Yup. I just rebuilt mine & I have ~130 across all 8 cylinders. Rebuild time is when they drop below 100, which is 120 - 20%.
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Unread 05-03-2013, 11:44 AM   #11
StrateLOSS
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Quote:
Originally Posted by MN59ZJ View Post
That the advice you gave is only true if you are doing the check wrong.
please explain




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Unread 05-03-2013, 11:59 AM   #12
MN59ZJ
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Quote:
Originally Posted by StrateLOSS
please explain
Quote:
Originally Posted by StrateLOSS
compression tests are accurate it showing compression psi relative to the cylinder next to it.
This is simply wrong (or at least poorly worded) and everything else that followed was based on this statement.
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Unread 05-03-2013, 12:16 PM   #13
StrateLOSS
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you did not explain it pal kudos to you, you'll now be ignored.


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Unread 05-03-2013, 02:37 PM   #14
PolkaPower
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Quote:
Originally Posted by StrateLOSS View Post
you did not explain it pal kudos to you, you'll now be ignored.


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I guess it's a str8loss!
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Unread 05-03-2013, 03:59 PM   #15
Candymancan
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Question mn59 when you neasured yours did you stwp on the gas pedal to open the throttle up.. Because if i dont do that my results are more in the 148-160 range with the throttle open they go up 20 psi.. And how many cranks is too many.. I cranked mine till the guague stopped going up which was probly 5-6 per cylinder.. Mine were with a burning hot engine not cold. I dunno why you said cold

And what are good nunberz for a 4.0 i think ill go ahead and check that engine too it just passed 200k and has never been checked before
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