Speedometer and Tach Fluctuations

By Ken Freund
April 28, 2017
Filed under RV Tech Q&A

 

Q:

I have a 1998 Tradewinds diesel motorhome that I purchased new. On a recent trip from Minnesota to Arizona, the speedometer and tachometer would fluctuate while driving between 60 and 75 MPH, while I was holding the accelerator steady. When I would engage the cruise control, the speedometer would still fluctuate between 60 and 75 MPH, while my speed appeared to remain steady. After stopping for lunch or at night, it would be OK for awhile, but then start fluctuating again. Do you think this might be the instrument panel, a bad sender, a poor connection or ground, or a diode?

Gerald Fenno | Sun City West, Arizona

A:

The fact that both gauges fluctuate together and at a steady speed indicate that the problem is not in the vehicle speed sensor or tachometer engine speed signal. Also, if the vehicle speed sensor signal was fluctuating, the cruise control would have problems maintaining a constant speed. So, yes, the problem likely lies in the dash cluster area. First, check the ground connection. Try running a new temporary independent wire with alligator clips, connected to a clean solid ground or directly to the battery ground post. The matching variations of the two gauges indicates a voltage fluctuation. If a good ground doesn’t clear up the problem (although I suspect it will), measure the voltage at the gauges with a digital voltmeter while the motorhome is driven at the speeds you mentioned. This motorhome is on a Freightliner chassis, so besides taking it to an RV shop for help, you can also take it to a Freightliner dealer.


 

Steps Not Working Correctly

I have an LCI retractable step on my 2011 Monaco Monarch motorhome. When I either retract or extend the steps, they will reach the full extension and the motor will continue to run, making a banging noise. It seems like there should be a limit switch to tell the motor to stop running. I called Lippert, and they said I should replace the complete motor system for $125. The motor works OK, it doesn’t know when to stop.

Don Downey | Boardman, Ohio

A:

Unfortunately, the limit switch that tells the motor when to stop is part of the motor assembly, and so it’s all replaced as an assembly. The banging noise is probably stripped gears from the motor-drive assembly, which further reinforces the need to replace the whole unit. You might be able to find a lower price online somewhere, but Lippert was right about the need to replace the motor assembly.


 

Dead Outlets

We have a 2010 Rexall 35-foot motorhome. The electrical outlets don’t work. I checked all the outlets and they all look good. The kitchen area and bathroom outlets work. Could the converter be the problem? Do you know where the converter is located?

Douglas L. Atchey | Via email

A:

The converter does not power the 120-volt AC outlets; it only produces 12 volts DC for low-voltage appliances, accessories and lights and battery charging, so this is not the culprit. First, check for a tripped circuit breaker in the onboard power-distribution panel. It’s also possible that there is a bad breaker in the panel. Ground fault circuit interrupter (GFCI) outlets are typically used for the kitchen and outside the motorhome, but it’s possible that the nonworking outlets were wired into this circuit instead of those required by code. Find the GFCI outlet and make sure it’s not tripped; reset if need be by pushing the appropriate button. If you have a higher-end coach, you may have an inverter/charger system instead of the converter. If this is the case, the inverter (Magnum, Xantrex, Go Power, etc.) may have a circuit breaker on it that could be tripped, so checking that is high on the list. If all the above pan out, then you could be looking at a wiring or receptacle issue. Sorting this requires a digital multimeter, and tracing the wiring from the circuit breaker using voltage, to each receptacle in that circuit. A wiring diagram would be helpful in this case. It’s not unusual for one receptacle in a daisy chain of receptacles to have a bad connection internally. This is best handled by a certified RV technician.


 

Shifting Advice

We have a 2003 Ford E-450 chassis with the V-10 engine in our 2004 Winnebago Minnie Winnie (31 feet) Class C. I’m especially concerned about manually downshifting on an upgrade, and what is a safe speed mechanically so as to not over-rev the engine on a long upgrade. Should I just put my foot to the floor and let the engine and transmission do whatever? We have no tachometer.

Bill DeMont | Via email

A:

The engine’s electronic controls have a built-in limiter which should prevent you from over-revving the engine at full throttle going up a grade. The automatic transmission also is designed to prevent over-revving even if a driver selects a gear that’s too low for the vehicle speed while descending a grade. Additionally, it will automatically force an upshift if the vehicle gains too much speed while in a manually selected lower gear to the point where the engine could exceed its redline.

You can determine for yourself what these speeds are in your specific motorhome. Simply accelerate at full throttle from a stop at the bottom of a long grade, with the shift selector in top drive gear. When it upshifts first, second and third gears, note the indicated speed and have your passenger write these down. These are your maximum shift points (which are at around 5,000 RPM). For a long engine and transmission life and fuel-economy reasons, I suggest you stay considerably below these points (about 20 percent) whenever possible. If you are concerned with the lack of a tachometer, you could add an aftermarket gauge, which is readily available and not too expensive.


 

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