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Old 02-09-2017, 05:22 PM   #1
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96 8.3 250hp tach not working

where is the sensor or pickup located, how do i check tach
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Old 02-09-2017, 05:26 PM   #2
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I think it runs off a pickup in the alternator.
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Old 02-10-2017, 07:59 AM   #3
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It could also be on the damper or on the bell housing.
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Old 02-10-2017, 06:49 PM   #4
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Quote:
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where is the sensor or pickup located, how do i check tach
I have an 8.3, 240 HP. Mine has a wire attached to the back of the alternater that goes directly to the tachometer.
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Old 02-12-2017, 02:22 AM   #5
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found a sensor on driver side bellhousing
how do i test tach or sensor with meter ohms or open/close signal?
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Old 02-12-2017, 04:56 AM   #6
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Clip an ohm meter, set to diode test, to the leads and quickly wave a steel screwdriver blade over the sensor end. The faster the wave, the faster or slower the tone. Been a while, since I checked one.
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Old 02-12-2017, 08:12 AM   #7
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Is it possible that the tach runs off the Allison TCM? If that's the case, the sensor you see on the bell housing would be the one that tells the TCM how fast the engine is spinning. If that sensor was bad though, you'd have issues with the allison shifting.

I know our alternator has no effect on the tach, but we have a one-wire "self exciting" type alternator (21SI)... so I always assumed our tach ran off the Allison. Maybe yours is the same? Just a thought...

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Old 02-14-2017, 07:09 AM   #8
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i found another 4 wire sensor passenger side on transmission no tach wire on alternator i assuming two wire is the tach on bellhousing
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Old 02-14-2017, 08:40 AM   #9
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If memory serves, I believe the input and output shaft sensors on the Allison are 2-wire. They are identical to each other too.

You have an md-3060, right?

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Old 02-15-2017, 09:39 AM   #10
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yes 3060
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Old 02-19-2017, 07:48 AM   #11
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The tach is driven by the alternator. The wires you are seeing on the bell housing are torque converter speed input and oust put.
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Old 02-19-2017, 04:48 PM   #12
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The tach is driven by the alternator. The wires you are seeing on the bell housing are torque converter speed input and oust put.
The OP's tachometer may very well run off of his tachometer...

But this has me wondering where MY tach gets it's signal. It's definitely not the alternator. I have a one-wire alternator (AC-Delco 21SI) and when it started overcharging on me last summer on our way home from vacation, I had to disconnect it from rest of the electrical system totally. I hot wired it so I could keep the chassis battery charged off of the generator while driving. And my tach worked just fine.

I've got the same tranny - MD3060, but my engine is the smaller B series 5.9. The only sensor anywhere that would read engine RPM would be the input shaft sensor for the allison... it's on the bell housing. The back of the gage in the dash says "magnetic pickup" with some instructions on how the gage returns to zero once it's powered and something about not over-torqueing the potentiometer adjuster.

I've always assumed that my tach got it's signal indirectly from the input shaft sensor through the Allison TCM... but there is nothing on the Allison wiring diagram that shows a specific output for a tachometer, so I'm now second guessing my assumption.

Any thoughts?

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Old 02-22-2017, 10:15 PM   #13
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i have 96 spartan dp with a vdo tach 1 211 015 894 A 4 plug inlet 12v,ground,tach ground and tach signal. i took up a good diesel tach started engine needle bounce upward once moved counterclockwise pass the zero stop moving dose not move same as the original tach. i checked ground wires for open circuit all grounded, check power wire has 12v. did a continuity check tach ground and tach signal wire with ohm meter meter pointer moves. no tach wire off the back of alternator only one big red wire. i assuming the 2 wire sensor held on the a bolt on the bell housing driver side is the tach pickup? i tried to trace signal wire with signal generator wire harness to fat will have to cut into. i may run wire from the alternator to the tach. i didn't see a junction box with a wire tach signal label on it. i called vdo gage tech gave all info they lost for answers they forward to upper tech will email me back. i will connect both tachs to ford diesel idi see if they ruin or they still work.
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Old 02-24-2017, 11:23 PM   #14
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i located the magnetic pickup on top of the bellhousing for the tach, i removed the pickup tested it for voltage it was good, tested the tach it was good. the pickup not attached, i have the tach ground wire and tach signal wire touching each other but not the ground wire, next trying to find where in the wire touching.
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