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CAT 3306 Air Inlet and Exhaust System Problems Part 1

Caterpillar 3306 and 3304 Air Inlet Elbow

Caterpillar 3306 and 3304 Air Inlet Elbow

Overview of all Caterpillar 3306 Air Intake and Exhaust Issues:

A lack of horsepower could be many things but one of the most common areas to check is the air inlet and exhaust systems. Subsystems of the air inlet parts to inspect include the inlet manifold, aftercooler, turbocharger, crankcase, exhaust temperature, compression, cylinder head, valve clearance, pre-combustion chamber and camshaft lobes. This will be the first article in the series 10 part series on air inlet and exhaust problems with the CAT 3306 and CAT 3304 Engines.

Inspect the Air Inlet and Exhaust for Restrictions:

If there is an immediate lack of horsepower the first place to check (other than the fuel system) is to see if the air inlet or exhaust systems have been clogged by some kind of restriction or debris. Air flow through the air filter must not have a restriction of more than 30” (762 mm) of water difference in pressure.

Backpressure is defined as the pressure measurement difference between the exhaust outlet elbow and the outside air. For CAT 3306 engines with turbochargers the water difference in pressure must not be more than the 27” (686 mm) or 34” (863 mm) for CAT 3306 engines without a turbocharger. If the air filter is clogged or dirty simply replace with a new one. Also check the air inlet piping for cracks or wear.

Caterpillar 3306 Air Inlet Manifold Pressure Test Diagram

Caterpillar 3306 Air Inlet Manifold Pressure Test Diagram

Backpressure Test on Inlet Manifold:

In addition to the air inlet it is also wise to inspect the pressure of the inlet manifold. The efficiency of an engine can be checked by making a comparison with the information given in the rack setting manual. The rack setting test is used when there is a loss of horsepower but no clear sign of an issue with the engine.

The optimal pressure for the inlet manifold is found in the rack setting manual. To accurately check the inlet manifold pressure the baseline rating is for 29.4 in of mercury barometric pressure at 85°F with a 35 API rated fuel. Any change from these conditions can change the pressure in the inlet manifold. Outside air that has higher temperature and lower barometric pressure than the given above will cause a lower horsepower and inlet manifold pressure measurement than compared in the rack setting information. Air from the outside of the engine that has a lower overall temperature and higher barometric pressure will cause a higher horsepower and inlet manifold pressure measurement. Inspect the air inlet manifold for overall stability and functionality around the couplings. A loose fit around the couplings and/or clamps will cause a drop in horsepower as well.

Check API Fuel Rating:

The last place to check for air inlet manifold pressure issues is the fuel rating. Fuel ratings, given by API(American Petroleum Institute) are marked in numerical fashion. API Fuel ratings gauges how light or heavy the petroleum liquid in question is compared to that of water. If the fuel for the CAT 3306 is rated below 35 API the pressure in the inlet manifold can be more than given in the recommended rack settings manual. It is VERY important to make sure there is no restriction in the inlet and exhaust when checking the pressure of the inlet manifold. Any sort of air filter restriction or improper pipe or tubing can throw off the pressure test and give false readings. Different fuel blends specifically winter fuel blends can sometimes be rated at a slight different API rating other than 35.

Caterpillar recommends using the 4S6553 Instrument Group to check the engine RPM as well as the inlet manifold and exhaust pressures. The instrument group includes 4S6992 Differential Pressure Gauges, Zero Adjustment Screw, Lid, 8M2743 Gauge, Pressure Tap Fitting, 4S5991 Tachometer and 4S6997 Manifold Pressure Gauge. To accurately do a pressure test remove the plug and elbow and install a tees for testing the pressure.

To Summarize Part 1 of Air Inlet and Exhaust Issues:

• Check for a dirty or worn air filter
• Check for cracks in the connecting inlet piping
• Check for old or worn inlet manifold
• Test pressure on inlet manifold
• Check rack setting information for OEM Spec
• Test for API Fuel Rating
• Test inlet and exhaust backpressure

Air inlet issues on the Caterpillar 3306 and Caterpillar 3304 should be considered the same no matter if the engine is a DI (Direct Injection) or PC (Pre-Cup Injected). Overall these pressure tests on the inlet manifold are not difficult and can be easily repaired. Inlet system replacements are not expensive outside of the turbocharger which we will get into in Part 2 of our Air Inlet and Exhaust Troubleshooting series. In addition to air inlet issue check our article about Common Caterpillar 3306 Starter Problems.

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