Author Topic: question for Jay or other elec techs...  (Read 2677 times)

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427Fastback

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question for Jay or other elec techs...
« on: November 04, 2018, 08:43:05 PM »
I have a new Autometer Tach #6806 on my Cummins 12Valve in the Grizzly.This is a crank trigger tach...
The tach reads very close at idle speed and just gets worse from there.Does not go over 1500 rpm .Its just plain lazy...
I have contacted the techs at Autometer but they have stopped answering me...

So...first round I had four posts in the balancer 1/4x1/4..Tach read as it does now..Autometer said to change it to 4 machined slots.I milled (4) .500 wide x .250 slots in the balancer...This made it worse.I then put .500 keystock in the slots and this gave me .250 high towers.Tach is now back to its normal bad behavior.

I then replaced the crank sensor and this did not help...I pulled the dash apart today to see if I somehow crossed the two sensor wires when I spliced them together but I have them correct...

Is one of the wires on the sensor a ground ???

Anyone have any ideas...This tach is north of $400 US and has not worked since day one...
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

RustyCrankshaft

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Re: question for Jay or other elec techs...
« Reply #1 on: November 05, 2018, 01:46:32 AM »
I usually use the OEM tach on diesel swaps I've done or aftermarket gas tach's if I need to add a tach (especially for a Cummins swap) so I've never used that Autometer diesel unit before. If you check the sensor output directly with a meter or preferably a scope do you get a clean signal above idle that way?

It's a diesel specific tach, so is it using a standard mag pickup or something else? If it's a mag pickup stop by your local big truck store and buy a tach sensor or speedo sensor from there (they're about 35 dollars) although it probably won't have the same connector, the sensor will work fine.

jayb

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Re: question for Jay or other elec techs...
« Reply #2 on: November 05, 2018, 09:16:02 AM »
With two wires that would be a VR (Variable Reluctance) sensor, and you do not ground one of the wires, the signal comes out of the sensor as a differential AC voltage between the two wires, with increasing voltage and frequency as speed increases.  There is an amplifier circuit inside the tach that can discriminate this frequency and turn it into an RPM signal.  Trying a different sensor is a good suggestion, all the VR sensors are pretty similar and a new sensor should at least allow you to debug the problem, if not fix it entirely.  If its not the sensor, the tach circuitry is probably bad and you may be out of luck...
Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

BattlestarGalactic

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Re: question for Jay or other elec techs...
« Reply #3 on: November 05, 2018, 09:50:33 AM »
Interesting.  I'm no engineer, but from what I dealt with my buddy building an electronic speedo system for my mack he was concerned with how I machined the reluctor wheel that signaled the pickup.  The wave form produced must be very square or it will get muddy and not read correctly.  Sounds like what you are seeing.  He is now a retired radar installation guy(knows his shit).

Since you changed the slots/keyways and that produced a change I would then keep looking at that.  Maybe it is the tach, but how that pickup gets the signal can mess with it.  You may need taller towers to help with signal generation.  The wave form is not clear enough and thus it is reading slow.
Larry

427Fastback

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Re: question for Jay or other elec techs...
« Reply #4 on: November 05, 2018, 11:54:53 AM »
To clarify/add....
I do not have one of the wires grounded..I was curious thus the question...
It is a 1990 engine and they didn't have built in tach sensors yet..
The replacement tach sensor was a Autometer one.
I agree....playing with the slots/towers changes the reading on the tach so maybe something is wrong there.I have the towers and air gap set to Autometers specs.I will look deeper into it......Thanks
« Last Edit: November 05, 2018, 11:58:43 AM by 427Fastback »
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

BattlestarGalactic

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Re: question for Jay or other elec techs...
« Reply #5 on: November 05, 2018, 01:08:12 PM »
Going by Autometer website, it looks like they supply you with the sensor.   You would think it should be sensitive enough to read using their specifications for how to set up the balancer.

I still think it is something to do with towers and what the sensor sees.  Are the walls straight on the sides?  Sharp bottom corner?  The metal moving past the sensor creates a waveform output.  It doesn't care if it is a tower or slot.  Just that it changes height.   That difference has to be enough for the sensor to read it as it moves past very quickly at higher rpm.

How about this:   take two opposite posts out.  Yes, it should read 1/2 speed, but see if it reads more then 750 rpm(you only got 1500 out of it previously).  This should prove that the sensor is not picking up the signal correctly at higher RPM.  Maybe try taller post and see if it works better.

Just throwing out some ideas.
Larry

427Fastback

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Re: question for Jay or other elec techs...
« Reply #6 on: November 05, 2018, 01:25:05 PM »
Valid thoughts...I am going to put the dash back together today and fire up the truck....
I used .500 keystock in the slots.It is square cornered.It protrudes .250 above the balancer....
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

BattlestarGalactic

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Re: question for Jay or other elec techs...
« Reply #7 on: November 05, 2018, 02:07:05 PM »
Do you have room to make them 3/8" tall?  I'm not sure what the point of no return is on height?  Besides sensor mounting interference?

What is their recommended air gap?
Larry

RustyCrankshaft

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Re: question for Jay or other elec techs...
« Reply #8 on: November 05, 2018, 03:16:07 PM »
Another option besides machining the damper is to buy a tone ring with a spacer and bolt that to the damper so you get a good signal. You can get entire tach kits from Destroked or DieselConversions. Or you can get a free pattern all over the interwebs and have you friendly local sheetmetal shop waterjet one for you.

427Fastback

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Re: question for Jay or other elec techs...
« Reply #9 on: November 05, 2018, 04:19:07 PM »
Autometer recommended height is .250 with a air gap of .030-.050..

I already have a diesel tach kit and I probably paid close to $600 Canadian by the time I got it to my door...I have access to a Omax waterjet but I don't see the gain by making a ring...Its a lot of work just to find out I am getting a dirty signal..
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

427Fastback

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Re: question for Jay or other elec techs...
« Reply #10 on: May 12, 2019, 04:52:12 PM »
I finally quit working with Autometer's techs and just sent my tach back to Autometer.I didn't care what it cost I just needed it to work...I never heard from them at all but 3 weeks later UPS showed up with my tach ...Autometer sent me a new tach and trigger.No questions asked..I assume they found something very wrong with it..They paid the shipping back to me.

Anyways....hats off to Auto meter for standing behind their products.They could have played the warrant card hand as the tach was now 3 years old...
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

BattlestarGalactic

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Re: question for Jay or other elec techs...
« Reply #11 on: May 12, 2019, 06:47:52 PM »
Nice!!!  Glad to hear they stood behind their products.
Larry

fe-starliner

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Re: question for Jay or other elec techs...
« Reply #12 on: May 13, 2019, 09:53:40 AM »
+1 for Autometer.  Last year my Autometer Monster with shift light, playback, etc quit working.  I bought it back in 2007.  Obviously WAY out of warranty. I sent it back to Autometer just to see if it could be repaired.  They emailed me back that it couldn't be fixed, but offered to sell me the identical model tach for $85 plus shipping.  A deal I couldn't refuse.
1960 Starliner, 406-6V, TKO-600, 4.11 9"
1961 Starliner, 427 4V, SS700 5 speed, 4.56 9"
1968 F-100 SWB, 352 4V, C6, 3.25 9"
2012 Mustang, 226" V6, 6 speed auto, 3.31 8.8"