Diesel motorhomes, especially rear-engine diesel pushers, live a life that’s hard on fuel injection: long periods in storage, then long trips under heavy load, often in heat, far from home. Their most common injection problems come from fuel that degraded or picked up water in storage, injectors and pumps that wore over high hours, supply problems such as clogged filters, and heat. Many can be prevented with simple storage habits, and the rest can be handled even when you’re a thousand miles from your usual shop.
What’s in the back
Diesel pushers and large Class A motorhomes have used engines from Cummins, such as the ISB, ISC, ISL and larger engines in heavy coaches, and Caterpillar, including the 3126 and C7. Their injection systems range from HEUI on the Cat engines to common rail and other electronic systems on Cummins engines. Know your engine model, serial number and injector part numbers; they’re the first things a shop will ask for. For the Cat engines, see Cat C7 and 3126 HEUI injector problems.
Storage is the biggest risk
A motorhome may sit for months between trips. During that time:
- Fuel degrades, forming gums and sediment
- Water accumulates from condensation, especially in a partly empty tank
- Microbial growth can develop where water and fuel meet
- HEUI engines may start rough after storage as injectors respond to oil that’s been sitting
The first symptoms after storage are often hard starting, rough running and smoke, sometimes followed by a plugged filter on the first day of the trip.
Storage habits that help
- Store with a full tank to reduce condensation, following your fuel supplier’s guidance
- Change fuel filters before a long trip, not after the first breakdown
- Drain the water separator
- Exercise the engine and generator periodically, under load where practical
- Consider fuel treatments appropriate for long storage, following the engine maker’s guidance
The generator shares your fuel
Most diesel motorhomes have an onboard generator that draws from the main fuel tank. Its pickup is commonly positioned so it can’t empty the tank completely, leaving fuel for the engine. Two consequences: contaminated fuel affects both engines, and a generator problem may point to the same fuel issue that’s about to affect the main engine. If the generator starts acting up, check the fuel.
Common problems on the road
- Plugged fuel filters from contaminated fuel picked up at a low-volume station
- Power loss on grades from filter restriction, supply problems or worn injectors. See diesel loses power under load.
- Hard starting when hot at a fuel stop or campground
- Smoke under load
- Injector-related misfire codes
Carry spare fuel filters for your engine and know where the water separator drain is. Many on-the-road fuel problems end with a filter change.
When a component fails far from home
A roadside fuel injection failure doesn’t have to mean waiting weeks at a local shop that doesn’t have the parts. Options include:
- Having the local shop remove the injectors or pump and ship them for testing and repair
- Using an exchange unit, if one is available for your part number, to get moving sooner
- Having the coach towed to a shop that handles your engine
Mail-in service works wherever there’s a carrier. See how mail-in diesel fuel injection repair works.
Before a long trip
- Replace the fuel filters if they’re near their interval or the coach has been stored
- Drain the water separator
- Start the engine and generator and let both reach operating temperature under some load
- Carry spare filters and the tools to change them
- Write down your engine model, serial number and injector part numbers, and keep them in the coach
If you’re stranded
Get the coach to safety, then gather the basics: what happened, any codes, what the fuel filter looks like and where you last fueled. With those details, a shop can quickly tell a filter problem from a component failure.
Further technical reference: Cummins: diesel fuel storage and transfer. Use the exact engine/injector/pump service information for applicable procedures and limits.
Get help wherever you’re parked
DCT works on motorhome fuel injection systems and serves customers nationwide by mail. If your coach is down on the road, have the removing shop contact DCT with the engine and part numbers. We’ll tell you what to send and whether an exchange is available. Ask DCT for current service timing and any shipping or approval factors before committing to a travel schedule. If you’re traveling through central Kansas, contact us to schedule, and we’ll confirm which of our locations suits the coach.
Before you ship: Request a mail-in component review to confirm part-number acceptance, packing rules, authorization, return shipping and timing. Local appointments: Hutchinson or Great Bend.