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SPN 94 FMI 18

Fuel Delivery Pressure — Value too low (moderately severe).
The reading is below normal at a middle warning level — more serious than FMI 17, less than FMI 1.

What the SPN covers: Low-pressure fuel supply pressure feeding the high-pressure pump, after the lift pump and filters. More on SPN 94.

What FMI 18 usually points to: A developing under-condition that often precedes a derate. More on FMI 18.

Severity

HIGH — limit use, diagnose now

Low fuel supply can cause power loss, hard starting and pump damage. Address before working the engine hard.

Likely causes

  1. Clogged fuel filter(s)
  2. Failed or weak lift/transfer pump
  3. Air leak on the suction side
  4. Low fuel level or gelled fuel in cold weather
  5. Faulty pressure sensor

Checks & fixes (easiest first)

  1. Replace fuel filters and prime the system
  2. Check for air in clear lines or a sight glass
  3. Measure supply pressure with a mechanical gauge
  4. Check tank pickup and vent

FAQ

What does SPN 94 FMI 18 mean?

Fuel Delivery Pressure — value too low (moderately severe). The reading is below normal at a middle warning level — more serious than FMI 17, less than FMI 1.

Is SPN 94 FMI 18 serious?

Low fuel supply can cause power loss, hard starting and pump damage. Address before working the engine hard.

What should I check first for SPN 94 FMI 18?

Replace fuel filters and prime the system; Check for air in clear lines or a sight glass; Measure supply pressure with a mechanical gauge.