Base Engine Diagnosis

Chapter 3 - Shop Manual
To make sure this all works..
•	We need compression
•	Valves (intake and exhaust)
–	Valves serve two purposes: 
–	Sealing - during compression and power strokes 
–	Opening up of ports - during intake and exhaust strokes
•	Rings/Pistons
•	Head gasket

But…
•	Where do you start?
•	You need to find the “weak” cylinder
•	Logical Order - 
•	Smoke?
•	Power Balance Test
•	Compression Test
•	Check for Spark and Fuel at cylinder
Smokin!
•	White Smoke – 
•	Burning Coolant – 
•	Head Gasket or Crack in block.
•	Check for bubbles in radiator, blown hoses, radiator, etc.
•	Pressure from combustion is entering the cooling system!
•	Overheating? 190 deg F normal temp.
•	Check plugs, “white plugs” or “washed clean look” is going to show what cylinder is bad.. - Video
Smokin!
•	Black Smoke - Too Much Fuel, not enough air
•	Running “Rich”
•	Poor MPG, Lack of power
•	Caused by stuck open fuel injector (dumping fuel)
•	Check spark plugs, darkest plug = cylinder is going to have the problem!
Smok’in!
•	Gray/Blue Smoke - Oil Burning
•	When engine is started - Valve Seals (allowing oil to travel down guides into combustion chamber)
•	When engine is accelerated - Worn rings (Perform compression test)
•	When engine is de-accelerated - Worn Valve Guides
•	Under hood leaks = smoke on hot exhaust parts
Smoke?
•	Check Plugs!
•	Oil Fouled Plugs Will Cause a Cylinder to misfire - Video
•	“Washed” plugs (coolant) will cause a misfire
•	Soot (Fuel) will cause a plug to misfire!
Power Balance
•	Shows us power from each cylinder
•	Hook up Tachometer, OR just use your eyes and ears!
•	We drop (cut) spark, or fuel from each cylinder and observe vacuum readings and RPM drop
•	The cylinder with the least amount of change is the weakest one

When doing power balance,
•	Keep car running properly, do not overheat
•	Warm up to operating temperature
•	Beware of high voltage from spark plugs
•	Write down results for each cylinder!
•	O2 Sensors - Disconnect

Why do this,
•	A PB test pinpoints which cylinder is at fault when an engine has a “miss”.
•	The tech can then quickly check the cylinder for proper injector operation, and spark.
•	If the cylinder has a clean plug, good spark, and power to the injector.
•	Either the cylinder has a defect, or the injector is not opening.
Compression Testing
•	Check cylinder compression in all cylinders.  
•	Remove all plugs, Disable fuel system and ground or disable ignition system, block throttle plates open, install battery charger.
•	Install pressure gauge.

•	Crank engine at least 4 times (4 seconds) per cylinder and check reading on pressure gauge.

•	If two adjoining cylinders are low, it’s due to a blown adjoining head gasket.
•	If one cylinder is low, perform a wet test.
•	If compression test shows high compression on all cylinders, it is due to carbon buildup
•	If compression test shows low compression on all cylinders it is due to incorrect valve timing (jumped time)

Wet testing...
•	Wet test is performed when dry compression is low
•	Adding SMALL amount of oil to cylinder will help seal worn rings
•	This will pinpoint if it’s a ring, piston or a valve problem!
Diagnosis
•	If the wet test had better compression than the dry test, the problem is the piston rings
•	If not, then the problem is valve related
•	Then move on to combustion leak testing (next class)
•	Video