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02-09-2017, 05:22 PM
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#1
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Member
Join Date: Feb 2017
Posts: 37
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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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02-09-2017, 05:26 PM
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#2
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Senior Member
Country Coach Owners Club Solo Rvers Club iRV2 No Limits Club
Join Date: May 2011
Location: Vancouver, WA
Posts: 37,725
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I think it runs off a pickup in the alternator.
__________________
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft, HWH Active Air
Charter Good Sam Lifetime Member, FMCA,
RV'ing since 1957, NRA Benefactor Life, towing '21 Jeep JLU Rubicon Ecodiesel
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02-10-2017, 07:59 AM
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#3
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Senior Member
Join Date: Aug 2002
Location: Where ever I park it
Posts: 1,345
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It could also be on the damper or on the bell housing.
__________________
2005 Dodge Ram Four Door Dually Southern Comfort Conversion
2017 Forest River 365RK
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02-10-2017, 06:49 PM
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#4
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Senior Member
Join Date: Sep 2013
Posts: 979
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Quote:
Originally Posted by tony326
where is the sensor or pickup located, how do i check tach
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I have an 8.3, 240 HP. Mine has a wire attached to the back of the alternater that goes directly to the tachometer.
__________________
U.S. Army Retired, 2002 Beaver Patriot Thunder
40 Ft, CAT C12, 455 HP, 1550 Ft Lbs Torque
Towing 2019 Chevy Equinox, AWD Turbo Diesel
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02-12-2017, 02:22 AM
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#5
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Member
Join Date: Feb 2017
Posts: 37
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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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02-12-2017, 04:56 AM
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#6
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Senior Member
Join Date: Jul 2014
Posts: 35,317
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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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02-12-2017, 08:12 AM
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#7
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Senior Member
Join Date: May 2011
Posts: 1,707
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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...
-cheers
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02-14-2017, 07:09 AM
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#8
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Member
Join Date: Feb 2017
Posts: 37
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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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02-14-2017, 08:40 AM
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#9
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Senior Member
Join Date: May 2011
Posts: 1,707
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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?
Cheers
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02-15-2017, 09:39 AM
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#10
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Member
Join Date: Feb 2017
Posts: 37
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yes 3060
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02-19-2017, 07:48 AM
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#11
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Senior Member
Join Date: Mar 2016
Posts: 107
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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.
__________________
1998 Fleetwood American Tradition 40VS
Cummins C8.3 300 HP Mechanical Injection Pump
Allison Transmission
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02-19-2017, 04:48 PM
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#12
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Senior Member
Join Date: May 2011
Posts: 1,707
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Quote:
Originally Posted by badturks5
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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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?
-cheers
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02-22-2017, 10:15 PM
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#13
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Member
Join Date: Feb 2017
Posts: 37
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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.
__________________
1996 35ft kountry star 8.3 diesel pusher, 6sp Allison trans, 1280w solar power system
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02-24-2017, 11:23 PM
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#14
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Member
Join Date: Feb 2017
Posts: 37
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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.
__________________
1996 35ft kountry star 8.3 diesel pusher, 6sp Allison trans, 1280w solar power system
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