Tach Intermittently Going to Zero

Met our Canadian Snowbird friends for dinner this evening.  They will tour Florida for most of November and we will meet them again at Thanksgiving at the CG.  It is great to see them again.

I am asking this question for them.  He has a 2005 or 6 HR Neptune with a 300HP Cummins and a 5-speed Allison Trannie.  While driving his Tach will go to zero or oscillate between the engine RPM and some lower value.  There is no change in engine RPM when this happens.  He has had it to the Dealer and Wildwood Service Center and naturally it did not fail for them.  The coach is running well.  While it could be anything from a corroded/loose connector to a failing sensor, I will greatly appreciate your input.

We are going to look at it when we meet in FL and I would like to go armed and will appreciate your answers to the following (and anything else you think I should know):

1.  Is the sensor in the engine or the transmission (where do we look for the sensor)?

2.  Is the sensor prone to intermittent failure?

3.  Is the Tach Gauge fed directly from the sensor or is it fed from the ECM?

4.  Do you know of any measurement checkpoints to help isolate the problem?

It should be obvious that he does not have a chassis or coach wiring diagram and has not been successful getting them from Monaco. 

Any help you provide such as sensor description, location, etc. will be appreciated.  It would be a stroke of luck if we could come across a wiring diagram.  Appreciate your help on this.

I know that upon reading this you are either taking a deep breath and saying "Oh my God" are laughing hysterically.  Both Cory and I have always worked under the assumption that it doesn't cost much more for someone to fix our mistakes (if we make any) than to fix the original problem and we have so much fun doing it, learn a lot from the experience and often times save a peck of cash.

What kind of chassis is it built on?

Sarge, can't answer that, just assumed that it was a RoadMaster chassis since it is made by Monaco.  I do know that he has Hydraulic Brakes instead of Air which may rule ou the RoadMaster.

Until I meet with them I can only communicate by Email.  I will send him a note this evening.

I have a similar problem with my American Tradition,, my tach will GAIN 200 to 500 RPM and hold it for several miles.  I intend to ( when convenient) remove the wires at the tach head and clean each connection, I believe this will correct it. When mine does this, I can rap the gauge with my knuckles and it will return to normal for many miles.>>>Dan

With problems like this I've had good luck using [urlhttp://www.caig.com/][/url] Deozit. It's not an abrasive contact cleaner. You just spray it on the pins of the connectors.

Sarge, it is a RoadMaster Chassis.

Sounds like a bad connection to me too. When you get the wiring diagram and trace the wires clean the connections well and consider using a dielectric grease to prevent future corrosion. Probably should check the wiring diagram really well for all connectors along the path. Could be some other effects that are not being noticed if an entire connector is getting bad. We had a bad connector and bad ground cause no end of trouble with my wife's CanAm.

Thanks Walt, I was asking because Freightliner has a pretty good network for chasing that stuff down. But on a Roadmaster chassis I'm not sure who to call other than Monaco. 

yfx4, thats part of the problem "no Wiring Diagrams".  Hope someone out there can help with getting them>

New information.  My friend has arrive at the CG.  While he has no wiring Diagrams for his 2005 HR Neptune with a 330hp Cummins, his Owners Manual does state that the Tachometer is fed from the Alternator.

We are going to check the wires for tightness and corrosion but will appreciate any input you may have. 

Obviously, the Tach is being fed by the AC from the alternator prior to it being rectified for charging the batteries.  The AC must then be converted by a frequency sensitive device to feed the Tach. The previous statement is pure supposition and will appreciate someone verifying or correcting me.

Assuming that I am correct, is this converting device usually in the alternator, in the Tach or a separate module between the Tach and the Alternator.

All input is valued.

Start with the simple stuff and work toward the more expensive.>>>Dan

weewun said:

New information.  My friend has arrive at the CG.  While he has no wiring Diagrams for his 2005 HR Neptune with a 330hp Cummins, his Owners Manual does state that the Tachometer is fed from the Alternator.

Click to expand...

If it is  fed by the AC from the alternator, how would a slipping alternator belt respond to the tach?

The 2005 Neptune Cummins engine is an electronic controlled one.  The Tach feed is from the ECM - not the alternator.  Most likely a missing ground or loose ground on the tach itself causing the problem.  A Cummins shop can check the ECM and determine if the Tach has been fed the correct readings or if it (the ECM) is failing.

I have a drawing for the 2006-2007 Cayman/Neptune.  If your friend would like it let me know rbdtanasi at yahoo dot com and I will send them.  It is one PDF and is in color.  If he takes it to Office Max or Kinko's (now FedEx Office) they can print it on a 24 x 36 sheet which will be much easier to read.

Rex

Rex, appreciate the input.  The statement about being fed from the Alternator came from the Owner's Manual and may be true in that the Alternator is feeding the ECM.

If you will send me the PDF file I shall get it printed and give it to him (he is not compter savy).  I am "[email protected]".

Thks

Walt don't put a lot of faith in what the manual says.  It has many errors as does the one for my 01 Diplomat. 

The file is on its way.

Rex