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Penta 5.7Gi Compression Test?

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VIPNiSS

New member
I am looking at purchasing a boat this Saturday and it has a Penta 5.7Gi motor with a SX Stern.

I am wanting to perform a compression test on it before I purchase it. What is the best way to do a compression test on this motor? I have read so many different ways and I think I have just confused myself.

From what I understand so far these are the steps that should be taken. Please correct/add if I am wrong.

  • Throttle should be wide open
  • Unplug all spark plug wires
  • Take out all the plugs
  • Screw in the compression test gauge
  • Turn it over 3-5 times until it gets maximum compression on gauge
  • Repeat on all cylinders
 
You have most of the basics, you need to either ground the lead from coil to dist or disconnect coil. Do not need any arching, possible fuel vapors or raw fuel bein pumped out of cylinders into engine compartment. I also recommend a fire extinguisher close by, just in case. Hopefully you dont need it but better safe than sorry.
 
I'll second the suggestion of disabling the ignition coil's power source.
Fuel Injected - GM Throttle Body Injection

Remove both the (grey) 2-wire connector, with

purple and grey wires and the (black) 2-wire connector,

with pink and brown wires located at the

ignition coil.

Volvo Penta of the Americas

1300 Volvo Penta Drive

Chesapeake, Virginia 23320-9810

Disabling Ignition Systems

All Gasoline

Distribution: M Date: 01-2006 Binder: C

Service Bulletin

Group Number Version

05-1 7 02

Otherwise, the high tension voltage needs a path to Negative to prevent coil damage......, and even then there's a risk of accidental fuel vapor ignition.

VIPNiSS said:
  • Throttle should be wide open
  • Unplug all spark plug wires
  • Take out all the plugs
  • Screw in the compression test gauge
  • Turn it over 3-5 times until it gets maximum compression on gauge
  • Repeat on all cylinders
Click to expand...
Turning the crank over 3 to 5 times is only 1.5 to 2.5 compression cycles....... and that's if you're lucky.
You'll want at mininum 3 compression cycles, or in other words 6 crankshaft revolutions per cylinder test... and that's if you begin with a good comp stroke.

Your highest cylinder pressure and your lowest cylinder pressure readings should be no more than 10% of one another for a healthy engine... and ideally less than 10%.
This is relative only if the pressures themselves are good to begin with.


I'd not add oil to any cylinders for this test. (If you need an explanation, post back.)


.
 
Last edited:
Opppps....... that should have read:

See Vovlo Penta Service Bulletin before you attempt to do the cylinder pressure readings.
Also verify the engine serial number.

Disabling Ignition Systems
All Gasoline
Distribution: M Date: 01-2006 Binder: C
Service Bulletin
Group.... Number ..... Version
05-1.... 7 ...... 02


If GM Throttle Body Injection, Remove both the (grey) 2-wire connector, withpurple and grey wires and the (black) 2-wire connector,with pink and brown wires located at theignition coil.

If MPI, disable the crankshaft position sensor.

There is apparently an alternative to this regarding disabling an Ignition Relay unit.


.
 
Last edited:
Don't use the key to turn the motor over.Use a jump box or remote starter.Turn the motor over until the guage stops going up.Like Rick says disconnect the fuel system.
 
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