Engine compression values
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Super Member
Joined: Jan 2008
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From: UK
E55K AMG
Engine compression values
Whilst changing the plugs I decided to confirm the condition of the engine compression. I did this by removing the fuel pump relay and using a draper gauge.
All cylinder preassures showed approx 155-165psi which is good right?
........but the far left rear no.4 cylinder read over 180 psi (I repeated more than once just incase the gauge was out)
What are typical preasures on a new motor?
All cylinder preassures showed approx 155-165psi which is good right?
........but the far left rear no.4 cylinder read over 180 psi (I repeated more than once just incase the gauge was out)
What are typical preasures on a new motor?
Last edited by £ C43 £ AMG £; Apr 12, 2011 at 08:07 PM.
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From: San Diego
E55
Did you check with the motor cold or warm? Also depends if you cranked the motor the same amount of times per cylinder. Main thing you want to look for is consistency in all the cylinders. When I do compression tests I also like to do a leakdown test right after. That paints a clearer picture of what's going on in the motor.
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My brand new engine which i had just broken in shows 9,4 to 9,6 BAR (136-139 PSI) on all 8 cylinders. The engine is silly strong btw.
But like someone else already told you, readings strongly depends on many factors (altitude, car battery strength, consistency, of timing of cranking, even thickness of your engine oil, carbon deposits (cleanless of your engine)) etc.).
But main thing you are looking for is consistency (same pressure) thruu all cylinders. If all cyl.are within 5%, you are VERY good, althoug WIS is telling us that everything that is within +-1,5 BAR or +-22 PSI (that is almost 15% difference between cylinders!!!) is good and that cylinders must have kompression between 9,0 and 12,0 BAR (130-174 PSI). Wear limit is 8,0 BAR (116 PSI). So acording to WIS you are alright (except slightly high reading on cyl.no.4), but according to my experience, you have heavy carbon deposits on cyl.number 4 or you had some oil deposits in cyl. number 4 combustion chamber in the time of meassuring compression.
Hope that helps.
Last edited by Snogard; Apr 13, 2011 at 03:23 AM.
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Joined: Jan 2008
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From: UK
E55K AMG
thanks you guys, I found your info useful and glad I am well withinn spec, apart from high compression on No.4,,,,,,suppose its much better than being low. thanks Snogard for providing the MB SPECS
car was running for five mins before I started, so was not cold just slightly warm.
I have used 500ml of redex fuel injector cleaner over the last few months, maybe some sea foam next.
car was running for five mins before I started, so was not cold just slightly warm.
I have used 500ml of redex fuel injector cleaner over the last few months, maybe some sea foam next.
