Whats up with the tach?

[AccessMaster]

My tach has been very unreiliable for some time.
I pulled the dash (somewhat) to see what was up.
If I turn on the ignition the tach jumps to 1000 rpm with the engine off.
If I move any wires in the area the needle will drop to 0 and back to 1000 and several stops in between.
I removed what I thought was the offending wire. It has a steady voltage of 12 Volts. I can not make it fluctuate ... so the wire integitey seems sound. Removing this wire dropped the reading to 0 until it was reattaced.
It seems that I can touch almost anything to get the needle to move.
I put it back together, went for a drive and the tach works much better now.
Any helpful thoughts on this one?

[87MH]

My tach also deadheads at 1000 rpm with the switch on and the engine not running. I think that this is normal.

In connecting and disconnecting the wires, maybe you helped correct a bad contact.

From my observations on the forum, the dash on the P-32 chassis is a constant source of problems.

Mine is about as non-ergonomic as they come, and the present dash will soon be history. I have experienced a bit of tach and speedo flutter, but only minor glitches. I also have the usual nuisance light problems (low coolant, water in fuel).

The water in fuel is a real mystery, since I know there is no water sensor on the Xeppelin, and strongly suspect that the water in fuel sensor was only installed on the diesel fuel versions.

[90345]

My tach also exhibits intermittent fluctuations.

Occasionally while cruising at freeway speeds the tach will drop to zero - a simple "thump" to the face of of the gauge - and its back to normal.

? !

Obviously something is loose or has a bad connection because I also have other erradic symptoms: when shifting the gear selector from "drive" to "park" my back up camera monitor flickers.
This happens even when the monitor is turned off !

Two more items for the "to do" list.

[AccessMaster]

The back up camera automatically comes on when in reverse on my unit. It will flicker as you pass from drive to park since reverse is in between. I would not spend any time trying to solve that issue.

[90345]

Thanks for that tip.
One more "mystery" solved .

David

[buckwheat]

Although still new to this Airstream stuff, the tachometer problems that you folks are having can probably be narrowed down to a simple connection problem. That can mean anything from a loose wire to a corroded fuse. A typical tachometer uses a simple shaft with a needle indicator on one end and a magnet in the middle that rotates within two opposing wire coils. Electricity flowing through the coils produces a magnetic field that causes the magnet to align, thus moving the tachometer indicator. Simply turning on the ignition would provide power to the coils but in equal amounts so the needle shoud not deflect. The fact that it is deflecting indicates that one coil is getting less electricity, implying internal resistance somewhere in the circuit. Dirt, corrosion, loose connections all add up to extra resistance. I'll be bringing Silver Belle home this weekend (1987 345MH from Dr. Joe), the good Doc has provided all the manuals, including (I hope) a P30 Chassis manual with electrical schematics. I'll take a look at the manual when I get it and provide a better troubleshooting guide to help get everyone's tach back where it should be.

[87MH]

Great news on your purchase of the Silver Belle.

It appears as if we are aproaching enough input to get the various systems sorted out!

[Navigator]

Same problem, but fixed mine by wiping dirt out between the magnets and sensing needle, and surrounding areas.
Dick

[buckwheat]

Yee-haw! Talk about getting intimate with the hardware! Nothing like a good tear down and clean to get the innards good as new. So were you troubleshooting a tachometer problem that resulted in taking it apart or were you just rebuilding? Either way, a good cleaning fixes most things that become troublesome over time. Thanks for the info!

[Navigator]

Buck;
Was fixing the tack because the dancing needle gave me the whammi if I looked at it too long.
Dick

[AccessMaster]

Where was the dirt build up? External on the back of the tach or did you open the tach up to get inside?
I have had my hands all over the back of the tach, but I have not removed it for a further inspection.

[Navigator]

No, in this case the magnet was embeded in the fly wheel, and the sensor was a bolt on to the casting, and the sensor sent a signal to the display.
Dick

[buckwheat]

So in your case, the dancing tach was being caused by a gunked up sensor system, rather than debris inside the tachometer itself? For a while there I thought you had disassembled the tach, dirt in the magnets and all that. Your solution makes sense for the problem that you had, now if we could just figure out what makes the tach show 1000 RPM with the motor turned off...