RPM gauges wrong readings

[fotonews]

Here I go again...
RPM gauges don't read 0 rpm when engines off, any ideas what could cause this? With engines running they work fine.

 

[Bt Doctur]

some gauges "relax" when unpowered and work normally when powered

 

[wellcraft-classic210]

I am guessing that's the normal power off state --Related to internal magnets, balance etc

Do they read 0 with key on & engine(s) off ?

 

[GA_Boater]

I am guessing that's the normal power off state --Related to internal magnets, balance etc

Do they read 0 with key on & engine(s) off ?

Excellent question. Some gauges "freeze" when power is turned off.

 

[fotonews]

Thank you Gentlemen, I guess I will have to live with for the time being although messing around behind the dashboard I found a data cable 879981 A15. I have a feeling is to connect upgraded gauges... anyone has played with it?

 

[GA_Boater]

The cable is for SmartCraft gauges. Those doesn't look like SmartCraft tachs since they have analog hourmeters.

What kind of hookup is on the back of the tachs?

 

[fotonews]

GA_Boater, yes, they are analog gauges. Do I need one data cable for each engine or both info is in that one cable?

 

[GA_Boater]

Not very familiar with SmartCraft other than reading in the forum, but it's my understanding that the SC buss is supplied by both engines. I think with the cable behind the dash, it's more like the OBDII connector in cars/trucks. Diagnostic tools can be connected to the port to access the computer data for both engines.

It might be worth starting another topic about the cable. We do have more than a few Merc techs in the forum that know.

BTW - Have you had a chance to see if the tachs go to zero with the key on before starting the engines?

 

[Bondo]

Here I go again...
RPM gauges don't read 0 rpm when engines off, any ideas what could cause this? With engines running they work fine.

Ayuh,.... Find a different detail to fret over,....

 

[fotonews]

GA_Boater, yes, rpm gauges go to zero when key on engines off. I guess I will leave it as is since when boat running they work ok except a minor jump on the needle once in a while. Im checking on the smart craft situation to connect VV Mobile with my IPad to have back up gauges in a digital format.

 

[HT32BSX115]

Here I go again...
RPM gauges don't read 0 rpm when engines off, any ideas what could cause this? With engines running they work fine.

Howdy,

Just about all automotive gages and many *new* marine gages are going to "Stepper Motor" type gage movements. Completely normal since the actual stepper motors are driven by an ECM or other type "computer" gage driver system.

They all pretty much will freeze in the last "level" , go to ZERO, or some other "park" position after shutdown. Then when the power is applied to the ECM, some will do a full-scale "sweep" and go to the commanded position.

All is good! Go boating!

Hey, Howdy Bill!!

Cheers,

Rick

 

[achris]

Haven't heard of steppers in tachos, but I could also be too old to care ....

However, the older marine gauges are all 'unsprung', meaning that the movement is ONLY done with the driver coil and not against a return spring. This is/was done so the 'bouncing' of the boat doesn't affect the reading (as much). With a return spring, it's effect will vary with the rise and fall of the vessel, making it (more) inaccurate... And unsprung gauges stay wherever they like once the drive/power is removed. What you are seeing is completely normal, and every boat owner/driver on the planet is presented with these unsprung gauges. Please move on, nothing to see hear folks.

Chris.....