Compression test
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Joined: May 2023
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From: Endless Mtns. PA
2014 E63 AMG wagon 1965 Austin-Healey 3000 1970 AMC AMX
Compression test
So because of the marks in a few cylinders , I am going to perform a compression test. I can't seem to find much info online. I am guessing remove plugs and try to find the fuse(s) for fuel pump. Does the starter go until the engine starts or for a few seconds then stop? I am new to the whole" one tap on the button and the car starts in 3 seconds" thing.
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E550 Coupe 2wd (2016)
on mine there is a function in xentry where it cranks it and, apparently, uses the crank sensor to check compression.
if doing it old school then yes, i suppose pull the fuse. i rekon id do it when the eng is running and let it die to bleed the pressure? it will no doubt throw codes and complain, but should crank. youre supposed to do it with the throttle open, but it does open it a little on crank and hopefully it will not change while complaining about fuel and what not.
so unless someone else chimes in, try it and see what happens. post the car, eng and year too
if doing it old school then yes, i suppose pull the fuse. i rekon id do it when the eng is running and let it die to bleed the pressure? it will no doubt throw codes and complain, but should crank. youre supposed to do it with the throttle open, but it does open it a little on crank and hopefully it will not change while complaining about fuel and what not.
so unless someone else chimes in, try it and see what happens. post the car, eng and year too
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From: New Orleans Area
2015 E400 Sedan
take all plugs out & Kill fuel pump
Insert pressure gage into cyl 1 and then turn over engine until pressure maxes out and stabilizes.
Record pressure number - Repeat for 2-8 or however many cylinders you have.
IF an inline engine start fcyl 1 and do them in order
For V engine do one bank at a time.
Then compare numbers is one lower then rest?
IMHO: Lower than 140PSI or a difference between adjacent cylinders greater then 10% or between max and min cyl of 15% means you need to have it checked out.
But you say you have SCORING?
Then you do a LEAK DOWN test which is different.
take all plugs out & Kill fuel pump
Bring piston up to top for cyl 1
install leak down tester setup into spark plug hole
Insert air & Set regulator to some value - I like 3-5 bar (45-60 PSI).
THEN LISTEN - should be dead quiet
If you hear air leaking noise then you need to find it.
Check coolant bottle for bubbles and air noise = means head gasket issue or crack somewhere.
Check oil dipstick = Means piston rings normally are piston seal to bore stinks.
Check Tailpipe = leaky exhaust valve
Intake by throttle body (open blade) - Intake Valve issues.
Repeat for every cylinder.
Good Luck
Insert pressure gage into cyl 1 and then turn over engine until pressure maxes out and stabilizes.
Record pressure number - Repeat for 2-8 or however many cylinders you have.
IF an inline engine start fcyl 1 and do them in order
For V engine do one bank at a time.
Then compare numbers is one lower then rest?
IMHO: Lower than 140PSI or a difference between adjacent cylinders greater then 10% or between max and min cyl of 15% means you need to have it checked out.
But you say you have SCORING?
Then you do a LEAK DOWN test which is different.
take all plugs out & Kill fuel pump
Bring piston up to top for cyl 1
install leak down tester setup into spark plug hole
Insert air & Set regulator to some value - I like 3-5 bar (45-60 PSI).
THEN LISTEN - should be dead quiet
If you hear air leaking noise then you need to find it.
Check coolant bottle for bubbles and air noise = means head gasket issue or crack somewhere.
Check oil dipstick = Means piston rings normally are piston seal to bore stinks.
Check Tailpipe = leaky exhaust valve
Intake by throttle body (open blade) - Intake Valve issues.
Repeat for every cylinder.
Good Luck
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Joined: May 2023
Posts: 463
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From: Endless Mtns. PA
2014 E63 AMG wagon 1965 Austin-Healey 3000 1970 AMC AMX
OK so the procedure is the same for the M157 as anything else. I am just used to holding the key to get the engine to turn over compared to a quick push of the starter button. Trying to figure that part out.
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m157 SL63
Thread Starter
Senior Member
Joined: May 2023
Posts: 463
Likes: 169
From: Endless Mtns. PA
2014 E63 AMG wagon 1965 Austin-Healey 3000 1970 AMC AMX
I haven't tried using the key yet and assumed it was also a momentary contact to initiate the start. I will test that.
