Backfiring When Towing Travel Trailer

November 7, 2003
Filed under Trailer How To

Q. My 1992 Ford Bronco has developed a problem recently. It has a 5.8-liter V-8 engine, and I pull a 26-foot travel trailer. The problem is that when I begin to tow, it develops a popping noise in the engine that sounds a lot like backfiring. It will lose power and the only way I get it to stop is to come out of the throttle and shift it down, keeping the rpm above 2,500 or 3,000.

On hills that I normally pull in second gear at about 38 to 40 mph, I drop into first at about 20 to 25 mph. When this happens, I cannot use throttle but have to come almost completely out of it.

When it is not towing, it is very smooth and runs fine. Can you give me some suggestions of what may be causing this?

— C.N., Hillsboro, Oregon

A. This is a classic symptom of fuel starvation in a gasoline engine. What happens is, when towing, more fuel is required than when driving solo. Something in the fuel system is limiting fuel
delivery so just enough is available for solo requirements. The simplest culprit is a partially clogged fuel filter, and that’s where I’d look first. Also inspect the fuel lines for kinks and other damage.

If the problem persists, have a fuel-pressure test run while the engine is under a full load while towing on a grade, when the engine is acting up. A weak fuel pump could be the cause, or the vapor recovery system isn’t letting air in to replace the fuel that’s pumped out (test drive with the fuel cap ajar to check this). — K.F.

Ken Freund’s more than three decades of auto-repair experience and 20-plus years of RVing helped him author numerous books and articles on vehicle repair. In addition to RV Clinic and Performance, he writes the Powertrain column in MotorHome magazine. Ken has been a California Automotive VO-Tech and Smog-Test Program Instructor and an ASE-certified Master Automobile Technician.

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