Code Details
| Display code | SPN 94 FMI 1 |
|---|---|
| SPN | 94 |
| FMI | 1 |
| OEM code | None listed |
| Manufacturer | PACCAR |
| System | Engine �?fuel system |
| Component | Fuel lift pump / fuel filter / supply lines |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | source backed |
| Source confidence | medium |
| Last reviewed | 2026-06-12 |
Plain-English Meaning
The PACCAR MX-11 is a 10.8-liter diesel used in Kenworth T680, T880, and Peterbilt 579 trucks as a lighter, more fuel-efficient alternative to the MX-13 in less-demanding Class 8 line-haul applications. The MX-11 fuel system uses a gear-driven lift pump to supply low-pressure fuel to the high-pressure injection pump. SPN 94 FMI 1 means supply pressure has dropped below the ECM threshold — most commonly from a clogged primary fuel filter. In Kenworth and Peterbilt fleet operations, fuel delivery pressure on the MX-11 is monitored by the ECM in real time. DAVIE4 and PACCAR ESA display the delivery pressure as a live parameter, making it straightforward to confirm whether a filter replacement resolves the fault or whether the lift pump itself requires further testing. Operating the MX-11 with low fuel delivery pressure accelerates high-pressure injection pump wear, so prompt filter replacement is the priority when SPN 94 FMI 1 appears.
SPN 94 FMI 1 is Fuel Delivery Pressure below normal range. DAVIE4 and PACCAR ESA display live fuel delivery pressure for the MX-11. Monitoring pressure before and after filter replacement is the key diagnostic test to confirm whether the filter was the root cause.
Common Symptoms
- Reduced power under load — the high-pressure pump cannot build adequate rail pressure with low supply
- Hard start or extended cranking time before the engine fires
- Rail pressure fault codes (SPN 157) may appear simultaneously
- Rough idle or stumble at low load as fuel supply fluctuates
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Clogged primary fuel filter
- Worn lift pump
- Air ingestion from fuel supply side
First Checks
- Replace the primary fuel filter — this resolves the majority of SPN 94 FMI 1 cases on the MX-11
- Connect DAVIE4 or PACCAR ESA and monitor live fuel delivery pressure before and after the filter replacement
- Check for water-in-fuel faults that may accompany SPN 94 — drain the water separator bowl if water is present
- If pressure remains below specification after filter replacement, test lift pump output with a pressure gauge on the pump outlet
- Inspect fuel supply lines for kinks or restrictions, and check the tank screen/pickup for debris
Can I Keep Driving?
Reduced power and potential derate. Address promptly.
Related Codes
Related Lookup Pages
Sources
- PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources PACCAR Inc. · oem · accessed 2026-06-11 · confidence medium
Source: PACCAR Inc., PACCAR / Kenworth / Peterbilt Service Support — MX Engine Resources. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - PACCAR Engine Technical Services PACCAR Inc. · oem · accessed 2026-06-10 · confidence medium
Source: PACCAR Inc., PACCAR Engine Technical Services. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - SAE J1939 Standards Collection SAE International · official · accessed 2026-05-05 · confidence medium
Source: SAE International, SAE J1939 Standards Collection. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Is the PACCAR MX-11 fuel filter the same part as the MX-13?
The MX-11 and MX-13 have different displacement and fuel system flow rates, so they use different primary filter part numbers. Do not install an MX-13 filter on the MX-11 without confirming part number compatibility. Confirm the correct filter specification using DAVIE4 parts lookup, PACCAR ESA, or the PACCAR online parts catalog using the engine serial number as the lookup key.
What is the service interval for the PACCAR MX-11 fuel filter?
PACCAR fuel filter service intervals are published in the MX-11 maintenance schedule. Intervals typically follow engine oil change intervals or annual mileage accumulation. Confirm the specific interval for the truck's spec and application in the Kenworth or Peterbilt maintenance guide.
Can the PACCAR MX-11 run the same fuel as the MX-13?
Yes. Both engines use ultra-low sulfur diesel (ULSD) fuel meeting ASTM D975 or equivalent. Biodiesel blends up to B20 may be approved depending on the model year and calibration. Confirm fuel specification in the PACCAR owner's manual for the specific truck year and spec.