Tachometer signal. ?

[rjwest]

Does anyone know what the Tachometer signal that goes into the Dash looks like?

Is it 8 pulses per 2 rpm( like a Gas v8? )
Square wave, Sign wave.....Any info appriciated.

Still considering TCI Trans controller, It needs a RPM input...

[gmctd]

It's off one of the three phase windings in the alternator - frequency and voltage is based on ratio of alt pulley to crank pulley.

Was a combo oil pump drive\tach sender on the early Diesel\4L80E trucks - 4 pulses per crank rev.

Shoud still be available.

[rjwest]

GMCTD , Where does the pump drive/ sender go?

Was it like the old Vacuum pump drive on 6.2.
Would it fit on 6.5 96 version....?

Thanks!!!!

[gmctd]

Yes - you'll see the small oil pump drive stub located there in your engine.
The tach drive version has a magnetic module on it.
Should be available from Avant, Peninsular, GM, etc.
Oil pump drive assemblies are interchangeable between all 6.2\6.5L engines, with and without vacuum pump, with and without tach sender.

More Power did an article on using the drive\sender on his 4L80E conv, Dr Lee did an article using the vacuum pump\sender for tach drive - each article has pictures.

[PerryMo]

Does the tach signal come from the alternator on the 1994 Suburban w/ L65 engine? :confused:

[Bobbie Martin]

AFAIK, all the electronic pump trucks use the alternator for the tach signal. Which is kind of silly since the computer gets its engine speed from the crank sensor and they could have used it or added a tach output from the PCM.

[gmctd]

That is correct, and I agree.

The CPS signal is input to the PCM already squared, and at +5v level.
And, so digitally precise.

Maybe the engineers were concerned with EMI\RFI noise.

Seems like an opto interface would have been cheaper than machining, storing, accounting for and installing a special diameter alternator pulley for Diesels only.

Or, maybe it's just me...... ;)

[whatnot]

Originally posted by gmctd:
It's off one of the three phase windings in the alternator - frequency and voltage is based on ratio of alt pulley to crank pulley.

Was a combo oil pump drive\tach sender on the early Diesel\4L80E trucks - 4 pulses per crank rev.

Shoud still be available. My 93 came with a 6.2L and has oil pump drive sender unit but still uses the alternater for the tach.

[gmctd]

Yep - that alt-tach connection is just a left-over from the '88 models, I would guess, before the solenoid-controlled transmissions.

[rjwest]

GMCTD: I assume the CPS ( ? Crank Position Sensor )
to be a 1 pulse per Revelotion

[gmctd]

It's 4 per rev, just like an ignition distributor off the camshaft

[Bobbie Martin]

Still considering TCI Trans controller, It needs a RPM input...
This is the least of your worries with this TCM. My guess is it needs an analog signal. Get a oil pump drive with a sending unit. It will provide the signal its looking for.

[rjwest]

GMCTD, Thanks for your patience.....

SO, If I buffered the signal with a high impedance amp. It should work as a tach input,equal to a V8. I'll ask TCI.

Thanks again for your help...
and all others who have responded....

[gmctd]

Check the Articles in the Member's Area for a tach buffer designed by Dr Lee - should also work with your requirements.

[MR.E]

I am installing a remote start and having difficulties with tach signal. I was hoping the remote start would be able to use the CPS input at the ECM but no luck.

The FSM shows a generator (alternator?) connected via a white wire to the tach. Anyone know if this is the white from the alternator? I assume this is not a square wave but a voltage.

Found the tach buffer article here (http://www.thedieselpage.com/members/features/swangertach.htm)

rjwest - Did you ever get this to work?

Has anyone else successfully installed a device (remote-start, turbo timer, trans controller) that required tach signal? How did you do it?

Thanks in Advance!

Eric

[rjwest]

No, not yet, still deciding if T-com trans controller is worth the effort,

Going to try ( 1 more time ) to get control of
the TCC lock up...


.

[Mainous]

Bringing this to the top again. I know the tach signal comes off of the alternator. Does anyone know which wire? I went to have my truck run on a dyno this morning and the operator didn't know where to pick it up.