TROUBLESHOOTING
Page 89
ENGINE CRANKS — WILL NOT START
ENGINE MISFIRES — CODE(S) PRESENT
Possible Cause Correction
1. Slow cranking speed. 1. Check corrections listed in preceding chart, ENGINE WILL NOT
CRANK.
2. Code(s) present. 2. Correct cause of code(s). Refer to ENGINE MISFIRES — CODE(S)
PRESENT chart.
3. No fuel to engine. 3. Check for fuel in the fuel tank. Check for plugged fuel tank
connections, restricted or kinked fuel suction lines, fuel transfer
pump failure or clogged fuel filters (including the pre-pump filter
screen).
4. Defective fuel transfer pump. 4. Check transfer pump for minimum output pressure. Change fuel
filters if low. Look for air leaks and recheck pressure. If still below
minimum, replace transfer pump.
5. Poor quality fuel, or water in fuel. 5. Drain fuel from tank. Replace fuel filters and fill fuel tank with
MACK-specified diesel fuel.
6. Incorrect engine oil viscosity. 6. Drain oil. Replace oil filters and fill crankcase with recommended
grade oil.
7. Low compression. 7. Check cylinder compression. If low, refer to LOW COMPRESSION
chart.
8. Faulty EUP fuel-return check valve. 8. Check for free poppet movement.
9. Faulty electrical connections. 9. Check electrical connections at ECU, engine position and
engine-speed sensor connections.
Possible Cause Correction
1. Code(s) present. 1. Correct cause of code(s). Check harness, battery and ground
connections. If code(s) remains, replace ECU. If code is still present
after replacing ECU, reinstall original ECU and refer to item 7 in
ENGINE MISFIRES — NO CODE(S) chart.
5-111.bk Page 89 Monday, July 10, 2006 2:26 PM
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