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Tach-Engine Hours
Bruce
Member Posts: 167 ✭✭
One of my winter projects is to replace my erratic tachometer that also has the engine hour display on it, on my 2004 250FV. I have found a brand new identical tach, but my question is, does anyone know if the engine hours are stored in the tach or in the PCM (computer)? Hence with a new tach, will I read 0 hours or will my accurate engine time still be displayed?
Thanks in advance
2004 250 FV
Comments
You can overdrive the meter on the tach with an oscilloscope.. its easier to do with one smart enough to set a timer.
the PCM will know the true hours... the PCM doesn't converse with the hour meter, at all. It just ends a pulse through the tach wire representing firing cycles.
the Tach, if you order it (assuming Faria, but it doesn't matter either way) directly from the factory ~can~ be calibrated by them to read hours, making them match.. or.. you can hook an oscilloscope to it and send a slightly higher voltage to the meter than it is expecting- you may have to jump past the first capacitor to do so... the slightly higher voltage 'overdrives' the meter, logging more hours quicker... or.. you can send the proper voltage to it (safer, no need for surgery) and use the scopes timing feature...
I thought about this long and hard when I installed my new tach/meter, and then said to myself "if I was to be in the market for a boat, I wouldn't look at the hour meter on the dash except to see if it had been replaced"... the PCM stores the number you will be most interested in seeing- and a whole lot more.. If I were to survey, that is the # that matters...
my recommendation to you, for whatever value it has, is to service your boat completely in this offseason, install the new tach/meter, and amend your maintenance log book accordingly- it'll be easier to track starting fresh, and so long as you don't overshoot an interval, you'll never guess again about what time it is for what maintenance procedure..
I just replaced all my gauges as well. The new tachs will still read 0 hours. My dealer told me the hours are stored in the engine computers and he as a Mercruiser Certified dealer is also noting the hours. I also took a picture of the old tachs as well as have the old tachs still in my possession. There really is not anything else we can do that I know of.
Good Luck with the new gauges. I had the Faria gauges and am excited to get out from under them.
Now I wish I could find a reasonably priced code reader to plug into the interface socket for my Merc 5.7
Geez, what good is diesel anyways! :P
....just another reason to have vesselview. It gives you the hours right from the PCM.
Dream 'Inn III -- 2008 400 Express
PC BYC, Holland, MI
The hour meter has the hour glass symbol in the left hand side of the hour meter display. Simply applying power to the gauge would not clock hours without a pulse to the Sig. post of the gauge. What I found that will work (at least for the gauge model described) is a Sho-Me LED flasher Model
SHO-ME LED FLASHER 11.1005.SF
I connected my gauge to my power supply, along with the sho-me flasher (it's 12VDC as well). I then connected one of the led flash output wires to the sig wire of the tach. My hour glass symbol started to flash and my tach needle started to pulse between 0 and 200 RPM, some what of an erratic pattern on the hour glass symbol flash, so I momentarily touched the white wire of the show-me flasher to 12VDC (doing this cycles the led flashed output to different flash patterns). While changing the flash pattern I would watch the hour glass symbol on the tach and look for a stable cycle of the hour glass symbol, i.e. 1 second on, 1 second off, etc.. After changing the led flash cycle on the sho-me unit a couple of times I found a stable cycle. so far my new gauge has clocked to 0.9 since hooking it up this morning. As luck would have it, which is rare for me, I had one of the sho-me flashers in my parts bin so I didn't have to buy it for this project. However the sho-me unit can be found on the internet for ~$25 - $30. If getting your hours on your new tach / hour meter is important to you then what I described above should work for you if it's the standard tach / digital hour meter gauge that requires a pulse on the sig. connection of the tach to start the hour clock.
The wiring hook-up is very straight forward.
+12VDC to Ign of gauge and red wire of show-me flasher
Ground to Gnd of gauge and black wire of sho-me flasher
Use either led output wire of the show-me flasher (yellow or blue, makes no difference) it's a 2 channel unit and connect to the sig post of the tach..
Momentarily touch the white wire of the show-me flasher to +12VDC to change the flash pattern if necessary.
As always pay attention to your connections, no short circuits, etc. I used a variable voltage current limiting bench power supply, however you can using any 12VDC capable of supplying at least 250mA+. My current (Amps) display on my power supply is showing 90mA to 100mA with this rig hooked up @ 13.8VDC..If you use an unregulated power supply, e.g. a car battery, wall transformer, etc. make sure to wire an in line fuse with the positive lead of of the supply, I would use 250mA fuse max.
Hope this helps.
It appears to be a thorn in the side of several folks replacing this type of unit, talking about taking the gauge to a TV repair shop to have a square wave signal generator hooked up, coming back days later to pick it up and hope the hours are correct and so on.
Disclaimer - I assume no responsibility for any damage that may occur as a result of following this advice. I have described my solution as accurately as possible, this may or may not work for your situation.
Edit: I was looking at my power supply display with my bad eye. :-) The modified values listed above (mA) are the correct values not the originally posted 900ma / 1A values.
Still clocking with no smoke @ 7 hours now.
Dream 'Inn III -- 2008 400 Express