Cylinder Pressure

[ramairmustang]

Okay does anyone know what the cylinder pressure should be around for my 95 Mark VIII. I want to test the compression. I have changed my plugs wires coils injectors and crank position sensor and still have a slight miss and my plugs have a rusty/brownish coloring on them. I am wondering if a gasket is going or something.

 

[NoLimit95]

Compression ratio?

9.85

 

[98LSC32V]

Should be 180-200 psi on all cylinders. Most important thing is all cylinders should be pretty close to each other.

 

[Sapperfire]

Okay does anyone know what the cylinder pressure should be around for my 95 Mark VIII. I want to test the compression. I have changed my plugs wires coils injectors and crank position sensor and still have a slight miss and my plugs have a rusty/brownish coloring on them. I am wondering if a gasket is going or something.

is it all the plugs look rusty? or just a couple.. if you have a head gasket breach, itll more than likely be the 7 and/or 8 cylinders..you can also do an exhaust vapor test on the coolant bottle, if you do not have a litmus tester, just hook a normal coolant pressure tester to the coolant bottle and start the car and watch to see if the coolant is building pressure

 

[driller]

Should be 180-200 psi on all cylinders. Most important thing is all cylinders should be pretty close to each other.

Dry or wet?

According to the book, the lowest number should be no less than 75% of the highest number.

 

[Sapperfire]

Dry or wet?

According to the book, the lowest number should be no less than 75% of the highest number.

i like them to be within 10% of one another, and if you do have one that falls a bit low, pour a tea spoon of oil into the spark plug bore and re-test, this will tell you if its the 0-rings or not

 

[rayner601]

from http://en.wikipedia.org/wiki/Compression_ratio



Measuring the compression pressure of an engine, with a pressure gauge connected to the spark plug opening, gives an indication of the engine's state and quality. There is, however, no formula to calculate compression ratio based on cylinder pressure.
If the nominal compression ratio of an engine is given, the pre-ignition cylinder pressure can be estimated using the following relationship:

p=Po x CR~

where Po is the cylinder pressure at bottom dead center (BDC) which is usually at 1 atm, CR is the compression ratio, and ~ is the specific heat ratio for the working fluid, which is about 1.4 for air, and 1.3 for methane-air mixture.

Read the whole page as I can't copy/paste the formula correctly.
Hope that helps out.

 

[ramairmustang]

is it all the plugs look rusty? or just a couple.. if you have a head gasket breach, itll more than likely be the 7 and/or 8 cylinders..you can also do an exhaust vapor test on the coolant bottle, if you do not have a litmus tester, just hook a normal coolant pressure tester to the coolant bottle and start the car and watch to see if the coolant is building pressure

Yes all them look rusty colored.