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RV Tech Savvy: Surging Problem

Originally Published in MotorHome Magazine

We have a 2007 Winnebago Adventurer 35L on a Workhorse chassis with a GM 8.1-liter V-8 engine and an Allison 1000MH six-speed transmission. While running on level terrain at an approximate speed of 60–65 mph, the tachometer starts surging from 2,000 rpm up to 2,500 rpm, as if the transmission is trying to shift, but it never does. I may have driven anywhere from 25 to 30 miles before it starts surging. The surging can go on for two miles or as many as 100 miles, then stops and goes back to normal operation. I have had the transmission rebuilt, replaced the transmission control module, and replaced the spark plugs and wires. Additionally, I have taken my coach to Allison’s main district area shop in Houston, Texas, and other locations. I was told that without the Check Engine Light or a trouble code indicating there is a problem, that this issue cannot be diagnosed and therefore the problem is unable to be repaired. I would welcome any ideas or solutions that may provide a “fix” for this problem.
Bobby Pearson | Huntsville, Texas

The problem may not be the transmission at all. Surging is very often caused by a slightly lean fuel mixture, which could be caused by a number of things. Have a shop with a drivability expert run it while a professional scan tool is connected to check fuel-related parameters including fuel trim, etc. One of the most likely causes is a partial loss of fuel pressure coming from the pump. It might be caused by a partially clogged fuel filter, which should be checked first. Remove the filter and blow through it backward (opposite the arrow on the canister) into a glass jar, so you can check for any particles, water or other crud. I suggest writing the date and mileage on the new filter to make it easier to keep track of replacements. If the filter is clear and the problem still occurs, measure fuel pressure at the fuel rail. It’s quite possible that the 13-year-old fuel pump in the tank is beginning to fail.

Storage Suggestions
We live in south Florida and have a 26-foot Class C motorhome. When it’s not in use, it’s parked beside our house, uncovered (except for the tires). It’s plugged into 120-volt AC power via a 30-amp breaker. We run the air conditioner (set at 80-plus degrees Fahrenheit) and the refrigerator 24/7. I start the engine and the generator and run the water pump every two months. It will normally sit like this from August/September until March/April. Before we start out, I will get the oil changed, plus have the generator and air conditioner checked and serviced. We flat tow a dinghy vehicle. What else should I be doing to make our motorhome ready to get back on the road for another 5,000–6,000-mile summer trip?
Don Howle | Naples, Florida

I suggest that you refer to the maintenance section of the chassis manufacturer’s owner’s manual and perform the recommended inspections and service items such as belts, fuel and transmission filters, fluid changes, etc. Don’t forget coolant and brake flushes every few years. Also increase the start-up frequency to once a month. Allow the engine to come up to full operating temperature. It’s best if you drive it rather than just let it idle. This also moves the spot the tires rest on, reducing the chance of them getting flat spots. The genset should have a load on it, such as an electric heater or air conditioner. You didn’t mention the make, model or year of your motorhome, or which model power converter it has. Many of the older ones don’t have a good maintenance charging mode and tend to overcharge batteries. Check to make sure yours has a “smart” charging regimen to protect the batteries. Because Naples, Florida, is very unlikely to freeze, you shouldn’t need to winterize the water system. Finally, unless you’re actually keeping things in the refrigerator, you might extend its longevity by shutting it down, cleaning it and leaving the doors ajar while it’s in storage.

Freshwater Tank Overflows
We have a 1996 Country Coach Intrigue that’s in great shape. When I am hooked up to city water, it wants to fill up my freshwater holding tank and then overflows. We usually use the water pump to get water but want to be able to use city water with no problems. Any suggestions?
Norm Hardy | Meadview, Arizona

When the city water pressure feeds freshwater into the on-board freshwater tank, it typically is caused by one of the following: the fill valve is faulty (or left open), or the check valve in the outlet side of the water pump has failed. The latter would cause the city water to flow backward through the pump into the freshwater tank. In most cases, this check valve is integral to the pump and failures are common, especially when subjected to high water pressure. Shurflo makes a replaceable check valve for some of its pumps, (part No. 94-800-03). You can install a ½-inch inside diameter (I.D.) in-line check valve instead, which is available from plumbing supply and RV stores. To protect your water system, I recommend using a water pressure regulator to maintain about 45 psi.

More RV Tech Savvy Discussion

Ken Freund portraitKen Freund has been a contributor to MotorHome magazine since 1988, and has written Coach & Powertrain and its predecessor, Powertrain Q & A, for two decades. He has been an RV, camping and travel enthusiast since he was a child.



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