Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

● Hold the throttle to full open position to ensure the engine gets adequate air intake.
● Insert the compression tester into one cylinder spark plug hole at a time. Specified minimum value for
B2XX engines is 0.9 MPa (128 psi)]
● If all cylinder readings are within the Volvo B2XX specification [0.2 MPa or 28 psi] of each other, no
further testing is required and compression is considered optimal.
● If any of them vary by more than this value, a problem may exist in one or more cylinders. Specialized
testing equipment may be required to fully diagnose the problem.
● Spark plug re-tightening torque is 25 +/- 5Nm or 18 +/- 4 ft-lb.
What if the Compression is Too Low or Too High?
Consecutive low compression in all cylinders could mean that the problem of fuel washed cylinders exists. This
means that the engine has had too much fuel introduced into it and all of the oil has been washed off the
cylinder walls. The oil creates a sealing effect between the piston and ring assemblies and the cylinder walls of
the engine block. Without this thin layer of oil, the engine compression would be allowed to escape into the
crankcase. This is common with an engine that has a 'flooding' problem.
If the engine seems to run normally but is weak and puffs a small amount of bluish smoke, it could be an
indicator of worn piston rings and cylinder walls. In either of these events, use a small oil can and squirt a little
oil into each cylinder, then repeat the compression test. If the compression dramatically increases then you
have found the problem(s). If the compression readings do not change, then it would indicate a timing problem
between the camshaft(s) and the crankshaft of the engine. The timing chain or belt would need to be checked
for proper timing.
If you find the compression reading is very low or zero in one cylinder, it is highly probable that internal engine
damage exists such as:
● There is a 'blown' or weak sealing surface at the head to block mounting area, which basically means a
bad head gasket (likeliest condition).
● A valve could be stuck or leaking.
● If the compression is low or zero on two adjacent cylinders, it might indicate excessive camshaft
excessive wear or a broken camshaft (not likely with Volvos).
● The piston could have a broken connecting rod or a hole in it.
● There could be a broken valve spring or a bent push rod.
When the compression is found to be too high in one or more cylinders, this would be an indication of excessive
carbon buildup in the engine. It can only be corrected by performing a chemical de-carbonizing process on the
engine or by removing the cylinder head(s) and physically removing the carbon that is attached to the cylinder
portion of the head(s) and the tops of the pistons.
Combustion Chamber Deposit Removal. For Chemical Removal Techniques, see the FAQ link. Water
Techniques. [Tip] My check engine light came on while at the Blue Ridge Parkway, so I take it to my friends
shop and they determine the it's the O2 sensor, they run a further test which shows it’s voltage regularly
dropping well below the minimum, but this still doesn’t prove anything. They reset the light and it stays out. But
then, he takes a jar of water and using a section of vacuum hose connected to the vacuum port for the cruise
control he quickly dips the hose in the water repeatedly while reving the engine, not very high, producing plenty
of steam and a really small deposit of black on the ground under the exhaust pipe. Here is the technique:
● Engine should be fully warmed up.
● Connect an 18" vacuum hose from a vacuum port between the throttle and the manifold. I used the small
vacuum nipple on the manifold where the flame trap connects to the inboard side of the intake manifold. I