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Service Bulletin No. 2878
MODEL D4000, D4500, E4500, G4500, J4500	TYPE Service Information	SECTION/GROUP 04 - Brakes & Air System	DATE Feb 09, 2004
SUBJECT AIR SYSTEM OPERATION ON EGR EQUIPPED ENGINES CONDITIONS Service Information Only PDF Download - Click on file ->

Description:

Effective with unit number 55606 on D4000 / D4500 model coaches, unit number 62098 on E4500 / J4500 model coaches and unit number 62536 on G4500 model coaches, Motor Coach Industries ( MCI ) made changes in the air system to comply with Detroit Diesel's requirement that the new EGR equipped engines have naturally aspirated air compressors. This change was made by Detroit Diesel in order to meet the EPA requirements for 2002 / 2003 compliant engines.

Coaches Built Prior to the Affected Unit Numbers

These coaches utilize a "turbo cut-off valve" system in the air dryer purge valve. When the governor reached the cut-off pressure of 125 psi/862 kp, it signals the air dryer to purge, the turbo cut-off valve then shuts off all air flow to the air dryer.

After this initial purge, no air is released from the purge valve assembly until the next purge cycle. The air compressor used on these coaches is a two cylinder Bendix Tu-Flo 750 compressor ( part number 4L-7-75 ). During the time the governor is cut-out, the compressor continues to pump air. A valve located between the two cylinders allows air to flow back and forth between the cylinders, thus no air is pumped to the dryer.

Current Coach Design

These coaches utilize a Bendix BA 921 single cylinder compressor ( part number 4L-7-143 ). The circuit employed in these coaches is a discharge line unloading circuit. In this circuit, when the governor signals the purge valve that sufficient pressure has been reached, the purge valve opens the line from the compressor at the same time it purges the desiccant cartridge. The compressor then continues to pump air through the discharge line and out the bottom of the purge valve. During the entire time that the engine is running and the air system is not charging the reservoirs, an air flow noise will be heard emanating from the purge valve on the bottom of the air dryer that may be mistakenly identified as an air leak. By design, this situation is normal and should not be interpreted as a malfunction.

To confirm that in fact the system is functioning correctly, shut off the engine and this noise will cease. If it continues or other air sounds are heard, investigate further.

If you have further questions or concerns, please contact the MCI Fleet Support Technical Center at 1-800-241-2947.