A diesel engine is only as healthy as the fuel reaching it.
A plugged filter, water in the fuel, air leaking into the suction side, a weak lift pump, or a cracked line can all cause the same symptoms: low power, surging, hard starts, stalling, or a fuel pressure fault. Left alone, some of those problems damage expensive high-pressure pumps and injectors.
East Tennessee adds two seasonal problems. In winter, a cold snap can gel untreated fuel and wax up filters, so trucks that cranked fine the night before won’t fire at dawn. The rest of the year, humid nights put condensation in partly empty tanks. Filters and water separators are the first line of defense, and they need attention on schedule — not only when the truck quits.
What’s included with our Fuel System Repair
- Primary and secondary fuel filter replacement
- Draining and servicing fuel/water separators
- Water-in-fuel sensor and warning lamp diagnosis
- Gelled fuel and waxed filters — warming, filter changes, and getting the engine running
- Priming the fuel system and bleeding air after filter changes or running dry
- Finding suction-side air leaks — loose fittings, cracked lines, and bad O-rings
- Lift pump testing and replacement
- Fuel line and hose repair
- Crossover line and tank fitting leaks
- Fuel pressure sensor diagnosis
- Fuel heater and filter housing problems
- Pulling a fuel sample when contamination is suspected
What needs a shop instead
- High-pressure fuel pump replacement on many engines, which can mean major teardown and timing work
- Injector replacement on engines where it means pulling major components — some injector work is possible on site, many jobs belong in a shop
- Tank removal, cleaning, or replacement after heavy contamination
- Flushing a system contaminated with gasoline, DEF, or water all the way through the injectors
Put DEF in the fuel tank? Don’t start the engine — on many trucks, don’t even turn the key on, because that can run the fuel pump. DEF in the fuel system can do very expensive damage. Call before you touch the key.
Repair it where it sits, or tow it?
Filter changes, water separator service, priming, gelled fuel, lift pumps, and most line and fitting leaks are standard mobile work. If the symptoms point to filters or air in the lines, the truck is usually running again on the same visit.
A tow may make more sense when contamination has already reached the high-pressure side, when a high-pressure pump or injectors have failed, or when a big fuel leak makes the truck unsafe to work on where it sits. Diesel dripping onto a hot exhaust is a fire hazard — shut the engine down and move away from the truck.
Have this ready when you call
A few details up front help the mechanic load the right parts and tools and get it done in one trip.
- Symptoms: low power, stalling, surging, hard start, or no start
- Outside temperature overnight, if you think the fuel gelled
- Any fuel smell or visible leak, and where it seems to come from
- Fault codes or a water-in-fuel lamp
- When the filters were last changed and where you last fueled
Makes & engines we work on
- Freightliner
- Peterbilt
- Kenworth
- Volvo
- Mack
- International
- Western Star
Class 6 through Class 8 trucks, including engines from Cummins, Detroit Diesel, PACCAR, Volvo, Mack, Navistar, and Caterpillar.
Fuel System Repair around Knoxville & East Tennessee
We handle fuel system problems at truck stops, fleet yards, and on the shoulder. Low-power complaints often show up under sustained load, like I-75 north of Caryville or I-40 west up onto the Cumberland Plateau, where a partly plugged filter can’t keep up. Gelled-fuel calls cluster on the coldest mornings of the year, anywhere trucks parked overnight.
Highways we cover
Towns we cover
- Knoxville
- Farragut
- Maryville & Alcoa
- Oak Ridge
- Clinton
- Lenoir City & Loudon
- Sevierville & Pigeon Forge
- Morristown
Fuel System Repair: common questions
What are the signs of a clogged fuel filter?
Power loss under load, surging, hard starting, and low fuel pressure codes. A filter can flow enough at idle but starve the engine on a grade.
How do I know if my fuel gelled?
On a cold morning, an engine that cranks but won’t start, or starts and dies, is a classic sign. Cloudy fuel and waxy filters confirm it. Winter-blend fuel and anti-gel additives, added before the cold hits, prevent most of it.
Why does my truck die right after a filter change?
Air in the system. After a filter change the system has to be primed correctly; skipping that step, or a filter that isn’t seated, lets air in.
I put DEF in my fuel tank. What do I do?
Don’t start the engine, and on many trucks don’t turn the key on either. Call right away — the tank and fuel system may need to be drained and flushed first.
Can water in the fuel damage the engine?
Yes. Water causes poor combustion and corrosion and can damage high-pressure pumps and injectors. Drain the separator when the lamp comes on and have the source checked.
Do you replace injectors?
It depends on the engine and access. Describe the symptoms and engine model and dispatch can tell you whether it’s an on-site job or a shop job.