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-13 common rail fuel injection system requires consistent low-pressure fuel supply to feed the high-pressure pump. When fuel delivery pressure drops below the ECM threshold, the HP pump cannot maintain adequate rail pressure, resulting in reduced power and potential starting problems. The MX-13 fuel system is compact and designed for low maintenance, but a clogged filter or failing lift pump will trigger SPN 94 FMI 1 on Kenworth T680, T880, Peterbilt 579, and other MX-13-equipped trucks.
SPN 94 FMI 1 is Fuel Delivery Pressure below normal. On PACCAR MX-13 with the ECM managed through DAVIE4 or PACCAR ESA, fuel delivery pressure is monitored continuously. DAVIE4 displays fuel delivery pressure in live data alongside rail pressure �?a low delivery pressure with a low rail pressure confirms the supply chain fault rather than an HP pump or injector issue.
Common Symptoms
- Power reduction under heavy load
- Extended crank or hard start
- Rough idle, stumbling under acceleration
- SPN 157 FMI 18 (rail pressure) may appear with this code
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Clogged fuel filter (primary cause on the MX-13)
- Lift pump output degraded or failing
- Air ingestion through a loose fitting, cracked filter housing, or low tank level
- Restricted fuel supply line
- Fuel delivery pressure sensor malfunction
First Checks
- Replace the fuel filter �?if overdue, this alone resolves the majority of SPN 94 FMI 1 faults on the MX-13
- Connect DAVIE4 or PACCAR ESA and monitor fuel delivery pressure under idle and load
- Inspect fuel supply lines for restrictions, kinks, or soft collapse
- Check for air leaks in the fuel supply circuit, especially at filter housing connections
- Test lift pump output pressure if filter replacement does not restore normal delivery pressure
Can I Keep Driving?
MX-13 may derate under load. Avoid prolonged operation with low fuel delivery pressure to protect HP pump and injectors.
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-13 fuel filter the same between Kenworth and Peterbilt trucks?
Yes. Kenworth T680/T880 and Peterbilt 579/389 with the MX-13 engine use the same engine-side fuel filter. The filter location and part number are determined by the engine, not the truck brand. DAVIE4 or the PACCAR parts system confirms the correct filter specification for the engine serial number.
How do I know if the PACCAR MX-13 lift pump is failing versus the fuel filter being clogged?
Use DAVIE4 to monitor fuel delivery pressure after installing a new filter. If pressure returns to normal range, the filter was the cause. If delivery pressure remains below specification with a new filter and no supply line restrictions, the lift pump output is suspect. A manual fuel pressure gauge at the lift pump outlet provides a definitive test.
Can biodiesel blends cause faster fuel filter clogging on the PACCAR MX-13?
High-blend biodiesel (above B20) can cause wax formation at lower temperatures than ultra-low-sulfur diesel, leading to filter plugging in cold conditions. PACCAR recommends confirming fuel blend compatibility with the MX-13 fuel system specification before operating on high-blend biodiesel, particularly in cold climates.