Oil Pressure Test - Ford Ranger Maintaince And Repair Manual

A screw−in type compression gauge is more accurate and easier to use without an assistant
7. Install a screw−in type compression gauge into the No. 1 spark plug hole until the fitting is snug.
8. According to the tool manufacturer's instructions, connect a remote starting switch to the starting
circuit.
9. With the ignition switch in the OFFposition, use the remote starting switch to crank the engine
through at least five compression strokes (approximately 5 seconds of cranking) and record the
highest reading on the gauge.
10. Repeat the test on each cylinder, cranking the engine approximately the same number of compression
strokes and/or time as the first.
11. Compare the highest readings from each cylinder to that of the others. The indicated compression
pressures are considered within specifications if the lowest reading cylinder is within 75 percent of
the pressure recorded for the highest reading cylinder. For example, if your highest reading cylinder
pressure was 150 psi (1034 kPa), then 75 percent of that would be 113 psi (779 kPa). So the lowest
reading cylinder should be no less than 113 psi (779 kPa).
12. If a cylinder exhibits an unusually low compression reading, pour a tablespoon of clean engine oil
into the cylinder through the spark plug hole and repeat the compression test. If the compression rises
after adding oil, it means that the cylinder's piston rings and/or cylinder bore are damaged or worn. If
the pressure remains low, the valves may not be seating properly (a valve job is needed), or the head
gasket may be blown near that cylinder. If compression in any two adjacent cylinders is low, and if
the addition of oil doesn't help raise compression, there is leakage past the head gasket. Oil and
coolant in the combustion chamber, combined with blue or constant white smoke from the tailpipe,
are symptoms of this problem. However, don't be alarmed by the normal white smoke emitted from
the tailpipe during engine warm−up or from cold weather driving. There may be evidence of water
droplets on the engine dipstick and/or oil droplets in the cooling system if a head gasket is blown.

OIL PRESSURE TEST

Check for proper oil pressure at the sending unit passage with an externally mounted mechanical oil pressure
gauge (as opposed to relying on a factory installed dash−mounted gauge). A tachometer may also be needed,
as some specifications may require running the engine at a specific rpm.
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HOW TO USE THIS BOOK
WARNING
Be careful not to crossthread the spark plug hole.
COMPRESSION TEST