Compression Specs.


Old 10-10-05, 04:30 PM
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Compression Specs.

1986 Chevy Truck, 5.0L Carbed engine. Compression check on "cold" engine
gave the following result:
Left Bank, #1=190lbs, #3=190lbs, #5=195lbs, #7=200lbs
Right Bank #2=175lbs, #4=185lbs, #6=195lbs, #8=185lbs
This was a cold engine check, are the above readings within acceptable range?

Ran check because engine has no power, but is intermittant. Traffic light #1
truck won't get out of it's own way, traffic light #2 it has it's normal power.
Any ideas what would cause this intermittant problem?
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Old 10-10-05, 04:47 PM
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
That's a little high, but at that age, it's probably got some carbon on the pistons
How did the plugs look?
How old's the other stuff? Wires? Fuel filter? Cap..etc...

You'll want to do the comp test again anyway, with the engine warm
Then do a wet test after adding oil to each cyl.

Don't forget to block the throttle wide open during the test
Old 10-10-05, 05:12 PM
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Other Stuff

Hope I'm doing this right, the other stuff is around 2-3years old. Oil is leaking past the valve guides and the pistons are probably carboned up as you say.
Any other idea's what I might need to do regarding the power problem?

Thanks for the reply,
Old 10-10-05, 06:29 PM
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
For the compression test:
Crank the engine over for at least 4 compression strokes
It should build up and top out real quick
Low compression on ther first crank, slowly building up by four rotations is worn piston rings
Low and stays low is usualy leaky valves or a head gasket

3 squirts of engine oil for the wet test, if compression increases, the piston rings are worn, stays the same, valves or head gasket

You should be around 150 for this engine

As you can see your pretty high
Could be because the engine was cold or the throttle wasn't blocked open

Other stuff:
Basic tune-up would be a good idea, but rather than buy new stuff on this engine right now, I'd check the condition of the old
Until after you get an accurite compression test results anyway
Plugs condition and gap
Cap and rotor condition
Wires can check resistance if you have a VoltMeter
Coil...also test with a VM
Fuel filter, that's kinda hard to check, if you don't know how old it is, maybe get a new one
Old 10-10-05, 06:34 PM
Join Date: Nov 2001
Location: North Texas
Posts: 2,345

20% between the lowest and highest is acceptable,A good tune up including a EGR cleaning sounds like a good thing to do.Check all hoses for leaks.

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