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Old 11-15-2013, 08:22 PM   #1
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Tach and Speedo intermittently are eratic while driving.

2001 Monaco Dynasty 40 ft.
Just purchased in Texas. Drove it to Kelowna BC. A few times enroute with cruise engaged, the tach and speedo would start to swing 4-500 rpm and 10-20mph? I read in the Monaco manual that it could be the alternator? I checked with Western Star (Truck dealer here) and they told me that the ISC had a sensor on the flywheel that gives RPM....not the alternator. Any other owners have had the same experience?
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Old 11-15-2013, 08:34 PM   #2
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Intermittent electrical issues often speaks to a grounding problem, perhaps with the dash cluster itself. Also need to check your ignition switch--they can lose internal contact as they get older.
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Old 11-15-2013, 08:50 PM   #3
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Only problem I have had close to yours is that the entire dash has shut down for about 1 second a couple of times. I can't get it to stay broke so have not found what caused it but I suspect either bad ground or ignition switch.
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Old 11-15-2013, 09:37 PM   #4
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I have the ISB engine my tach stopped working at the same time my alternator went out. The cummins shop said the tach works off of the alternator. They put new one on and now the Tach works fine.
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Old 11-16-2013, 10:02 AM   #5
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Ground issues are common on motorhomes (and boats). Mine did the same thing. Clean the ground lugs and wires an you should be good. If the tach only is intermittent, the alternator would be suspect.
I use my GPS as an alternate speedo, BTW.
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Old 11-17-2013, 12:00 PM   #6
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Grounding points for dash?

Thanks Westie for your response and all others as well. Can you be a bit more specific as to which ground connections you are referring to? Under the dash, or exactly where are these located?
I am a new owner and have not had a chance to snoop much at the guts of this condo on wheels.
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Old 11-17-2013, 12:41 PM   #7
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Quote:
Originally Posted by 747guy View Post
Thanks Westie for your response and all others as well. Can you be a bit more specific as to which ground connections you are referring to? Under the dash, or exactly where are these located?
I am a new owner and have not had a chance to snoop much at the guts of this condo on wheels.
I had same issue with my 07 Neptune. Instead of tracing down the grounds I simply ran a new ground wire to the firewall. So far seemed to solve the intermittent gauge failure. Hope this helps.
Chad
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Old 11-18-2013, 01:01 PM   #8
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Your 2001 Dynasty probably has the ISC electronically-controlled engine. The tach signal does NOT come from the alternator, as on previous mechanical injection engines. The signal for the tach and speedo come from either the engine ECM or Allison ECM, so your problem is almost surely a bad connection, and faulty grounds account for almost 95% of those problems.

Removing your dash is not a major job, but neither will it be done in one hour. If you are lucky, your coach will have a dash access panel that can be removed above the instrument panel, and that MAY give you the access you need. If you must remove the dash, pull it out only as far as you need for access, and be ready to support it properly. Some of them are plastic and quite flimsy. They are especially prone to breaking in the area of the (way too heavy) Sony backup monitor that is supported by nothing but the plastic.

Once you have access, look to the firewall near the top. You may see as many as three buss bars with a multitude of white wires attached to them. At the end of each buss bar, there will be one very heavy wire about 1” long, leading to a bolt that goes into the firewall. That one heavy wire supplies the ground connection for all the other smaller wires. Using the straw on a WD-40 aerosol can, douse the entire buss bar—you want to hit the wires and the individual bolts that clamp the wires. Using a #2 square-drive (Robertson) bit, begin tightening each wire by FIRST loosening it, then reclamping it quite tightly. Pay particular attention to the heavy wire at each buss bar—loosen and reclamp it at the buss bar BUT BE SURE to loosen and retighten the large bolt that fastens that heavy wire to the firewall. After doing all this, there is a 60% chance your problem will have been solved. If not, it is STILL likely than a faulty connection, especially a ground, is still at fault, or that your ignition switch is intermittent. You can usually eliminate the ignition switch if only the tach and/or speedo act erratically. If the ignition switch is at fault, it is more common for it to interrupt ALL dash gages. If your ignition switch is not at fault, the faulty connection will be along the instrument panel itself. Although the fault can be in any wire sending a signal TO the instruments, it is more commonly the ground wire (for reasons I’ve not been able to decide).

If your fault is at the instrument panel, you will surely have to remove the instrument panel itself. Using a nut driver, loosen and retighten every electrical connection you can find. As a matter of routine, as one poster recommended, I do all this retightening, BUT ALSO run a daisy chain of wire connected by ring tongue terminals to every ground on every instrument on the panel and terminate it at one of the ground buss bars on the firewall. That is not necessary, and is surely redundant, but if you have the dash out already, it is what I would do.

Also, if you MUST remove your instrument panel, you will realize it is not a fun job, and anything you can do to preclude having to do so again is worth it. You might consider doing as many of us have done, and replace the ignition switch whether or not you think it is faulty. It is less than $20 at Advance Auto (BWD brand, part number CS81—from 70’s vintage Chevy truck). Further, it has been my experience on my present 2000 Dynasty, that the push-on connectors for my switch were loose-fitting, and no amount of squeezing them with pliers would fix it. I replaced them. Same goes for replacing the headlight switch, which frequently has its dash light dimmer portion become intermittent.

Lastly, however you can gain access to the many multi-conductor plugs behind the instrument panel, it is a good idea to uncouple them, spray with WD-40 and reassemble. On a piece of machinery that has probably over a thousand connections, it takes only one to cause you a problem. On my first DP, a 93 Dynasty, I chased one electrical gremlin after another, many of them intermittent, for months. All turned out to be the result of bad connections. I finally took the advice of a wise man, and systematically sought out every connection I could find of any kind, and either jiggled it to improve contact, or when possible I removed it, sprayed with WD-40 and reassembled. It took me almost all of one Saturday. I never had ONE SINGLE electrical gremlin after that. Sure, I had a fuel cutoff solenoid go bad, a windshield washer pump crap out, and clearance lights burn out…but I never had another intermittent “gremlin”. This will be much easier on your present coach, since the vast majority of your connections will be in the Front Run Bay under the driver's position, or in the Rear Run Bay on the passenger side at the rear. Remove every connection and retighten, clean and renew it and you will save yourself some really annoying on-the-road failures. That is the FIRST thing I did when I bought my present coach, which had a few gremlins. Should your fuel gage be erratic or undependable, it is probably for the same reason. Open the bay (permanent screws from underneath the coach) clean and renew all the connections, and add a redundant ground wire to the frame.

Good luck with your new coach!

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Old 11-19-2013, 07:27 AM   #9
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Mine does the same thing

747Guy
I also own a 2001 Dynasty tag Regent and my speedo does the same thing. It works just fine for hundreds of miles and then overestimates my speed by 10 to 20 mph for some random number of miles before returning to accurate speeds. It occurs randomly. That has been my only problem in the dash, and I have not dealt with it. I use my GPSs for my speed indicator anyway and of course, I drive at ~ 60 mph on the highway and my tach sits at roughly 1600 revs at 60 mph. One of the these days I will go after the problem, but as long as that is the only problem in the dash, I will solve it by relying on the tach and one of the GPSs set to the "dash board" function (I have 3 running all the time).

Good luck, and please post the solution if and when you find it.

Drive many happy and safe miles....

Gary
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Old 11-20-2013, 12:55 AM   #10
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We've cleaned and / or fixed all grounds. Thom added a ground from the alternator to the frame, one from the battery to the frame and one from the tech to the frame. Finally was told by Monaco to try adding a 330ohm load resistor across the signal line and the ground in on the tech in the dash.

All the problems seem to be fixed so far. Tech jumping, volt meter jumping and things going haywire when adding a load like turning the headlights on.
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Old 11-20-2013, 01:18 AM   #11
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IIRC there is a Vehicle Speed Sensor on the electronic engine rigs, on the trans. Could be dirty connections on that. In the ECM program there is a parameter Cummins refers to as "revs" which gives ecm the distance a toe travels each rev. The ecm uses revs times the VSS rpm times the gear ratio to get mph & miles traveled. IIRC.
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