Repair Info - Emissions Repair Explained
Overview | Component Testing - Doing It Right | Engine Integrity TestsEngine Integrity Tests
Underneath all of the emission control, fuel control, and spark control technology is an engine that basically functions the same as engines designed a hundred years ago. The engine must be fundamentally sound in order for combustion to properly occur and for emissions to be maintained at normal levels.
To ascertain basic engine integrity, a good technician should use power balance testing, compression testing, and, if necessary, cylinder leak-down testing.
Power Balance Testing
A power balance test can be useful in identifying uneven power contribution amongst all cylinders. This is done using an engine analyser.
To be effective, a power balance test must be preceded by other more basic testing. For example, the technician should not try to diagnose an HC problem with a power balance test if they haven't already completed the ignition systems tests, and fuel control tests.
Compression Test and Cylinder Leakdown Test
As each piston in an engine moves up and down, it compresses the air fuel mixture prior to combustion. If a piston is not able to compress the mixture enough, incomplete combustion and excess emissions will result. An engine's ability to compress the mixture is measured using a compression gauge. Variation in compression pressure should be no more than 10% from cylinder to cylinder.
If compression is found to be low, the source of the leakage can often be located using a cylinder leak-down tester. Basically this tool fills the cylinder with compressed air from an external source. To locate the leak, a technician just needs to locate the escaping air. Cylinder leakage typically occurs through an intake or exhaust valve, or past piston rings that are worn out.
Combustion Chamber Deposits
Unless the technician has a device called a boroscope that allows him or her to view inside engine cylinders, they cannot conclusively test for excessive carbon deposits. Therefore the only logical process to follow is to eliminate all other possibilities first. Only then is it reasonable to conclude that combustion chamber deposits are contributing to excessive NOx emissions.
Many techs have had good success with combustion chamber cleaning chemicals if applied correctly. Generally, the technician should apply 500ml of the combustion chamber cleaning chemical through a large vacuum hose and stall the engine. After all of the chemical has been induced into the engine, it is critical that the technician leave it soak overnight before restarting the engine.
On rare occasion, a second application may be necessary to remove the deposits. If this method is not successful, the only other way to remove the deposits is to disassemble the engine and clean the deposits off by hand.
