Aftermarket Tach. - Page 2 - PeachParts Mercedes-Benz Forum

polarisrmk · #16 04-22-2010, 01:27 PM

Quote:

Originally Posted by techguy512

The standard scheme uses variable reluctance sensor, so it's necessary to pass a constant current through the coil, and then watch for the voltage change as the pin passes by the coil face. The voltage produced is tiny (about 0.6V), and very short in duration, and it's the job of the tach amp to sense it and send a pulse to the tach of the proper amplitude and duration (5.5V, 3ms). The amp does this once per crank rev, and the diesel tachs are calibrated for that "one pulse per rev" signal.

Aftermarket tachs generally require a different amplitude, duration, and "pulses per rev" in order to work properly.

All that being said, I've got the aftermarket tach thing mostly figured out...

http://www.mbelectronicupgrades.com/Project-Aftermarket_Tach.html

Yes but that just plugs into the stock location.... I need something that will work out of the car.... i guess i could get the wire harness from the pnp and wire it up ..... is this possible? what tachs will it work with? Could you help me with the wiring?

300SD81 · #17 04-22-2010, 03:08 PM

Quote:

Originally Posted by polarisrmk

I am putting the engine in a boat .... I would like to not us the stock tach

Use the stock amplifier though, it outputs 12v pulses, should make it easy to drive an aftermarket tach.

thinktank · #18 04-22-2010, 03:09 PM

here is a link

thinktank · #19 04-22-2010, 03:10 PM

www.autometer.com

babymog · #20 04-22-2010, 03:17 PM

Buy a VDO that runs from the alternator, I've run them with no problems.

techguy512 · #21 04-22-2010, 03:28 PM

Quote:

Originally Posted by 300SD81

Use the stock amplifier though, it outputs 12v pulses

Actually, the stock amp outputs 5.5V pulses......

techguy512 · #22 04-22-2010, 03:33 PM

Quote:

Originally Posted by polarisrmk

... I need something that will work out of the car.... i guess i could get the wire harness from the pnp and wire it up ....

The wire harness from a PNP would be easiest, but you could use discrete wiring instead.

Quote:

Originally Posted by polarisrmk

...what tachs will it work with?....

Choose a tach you'd like to use and get the docs. From that we can determine if it will work....

Quote:

Originally Posted by polarisrmk

Could you help me with the wiring?

Yes. Is this going to be a freshwater or saltwater boat? Does your engine have the pickup coil and bracket installed already? Is the cable and connector on the pickup intact?

polarisrmk · #23 04-22-2010, 03:49 PM

Quote:

Originally Posted by techguy512

The wire harness from a PNP would be easiest, but you could use discrete wiring instead.

Choose a tach you'd like to use and get the docs. From that we can determine if it will work....

Yes. Is this going to be a freshwater or saltwater boat? Does your engine have the pickup coil and bracket installed already? Is the cable and connector on the pickup intact?

freshwater boat.... here is the thread

617 Turbo into a Boat

The pickup coil is there .... however someone cut the wire off when pulling something else out of the car at the pnp but if i remember correctly the tach amp plug harness is still on the car just no tack amp....

polarisrmk · #24 04-22-2010, 03:53 PM

Heres a question....

My 85 SD has the same round plug on it with no tach amp pluged in and in the fsm it says its a diagnostic port.... and my tach still works?

polarisrmk · #25 04-22-2010, 03:55 PM

Quote:

Originally Posted by babymog

Buy a VDO that runs from the alternator, I've run them with no problems.

My only thing against the VDO is that it is an external mount ... I have used one of them on a snowcat with a cummins. They work well but in the boat i want to mount the gauge in the dash.

techguy512 · #26 04-22-2010, 09:47 PM

Quote:

Originally Posted by polarisrmk

Heres a question....

My 85 SD has the same round plug on it with no tach amp pluged in and in the fsm it says its a diagnostic port.... and my tach still works?

You have a different system. In the late '83 to '85 models, the EGR computer controls the 3 wire tach. This will cause a lot of trouble for folks in the short term future as the EGR computers fail. They are 'unobtainium' now and in the future except as PNP treasures.

I'm assuming you're not transferring any EGR computer into your boat.....

babymog · #27 04-22-2010, 10:37 PM

I'm not aware of an external mount tach, mine have always been mounted in a standard hole in the dash.

Quote:

Originally Posted by polarisrmk

My only thing against the VDO is that it is an external mount ... I have used one of them on a snowcat with a cummins. They work well but in the boat i want to mount the gauge in the dash.

polarisrmk · #28 04-22-2010, 11:09 PM

Quote:

Originally Posted by techguy512

You have a different system. In the late '83 to '85 models, the EGR computer controls the 3 wire tach. This will cause a lot of trouble for folks in the short term future as the EGR computers fail. They are 'unobtainium' now and in the future except as PNP treasures.

I'm assuming you're not transferring any EGR computer into your boat.....

No i am not... But I did think about it

Totally kidding of course.

polarisrmk · #29 04-22-2010, 11:10 PM

Quote:

Originally Posted by babymog

I'm not aware of an external mount tach, mine have always been mounted in a standard hole in the dash.

And see the only one i have seen is a external mount ie pillar mount .... where do you get yours from? How accurate is it?

jbrianfoto · #30 04-23-2010, 10:08 AM

Hi -

I needed a tach for my 1980 300TD - found and installed this one from Tiny Tach -

http://tinytach.com/tinytach/diesel.php

It has a little piezo which bolts to any of your 5 fuel injector lines. Mounted the display on the center of my instrument cluster (just abouve the stearing column. It's got a backlit display and also counts hours.

Good luck !

Jeromie

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