question about a tach sensor
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Senior User
Joined: Feb 2013
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From: San Antonio , Texas
question about a tach sensor
I have a quick question about the tach sensor, swapped a 7.3 idi into my 82 truck and I have no tach right now. my question is if there is a difference between a 6.9 and 7.3 tach sensor, ive been unable to find a part number even through fords website for a 6.9 sensor. I may have a bad sensor but wanted to be certain that its not maybe the wrong sensor for an older tachometer. if anyone knows please let me know, thanks!
Fleet Mechanic
Joined: Aug 2011
Posts: 1,570
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I found an easy way of testing the tach sensor (well any magnetic pickup sensor) pull the sensor out of the truck and take your multi meter and set it to AC volts (low range) and probe the socket, then find one of those heavier wall adapters 
and place the pickup end against it and you'll get a reading that will diminish when you pull it farther away or increase when brought closer. (all your doing is using the magnetic field from the adapter to make the sensor work, don't worry about the cord)
and place the pickup end against it and you'll get a reading that will diminish when you pull it farther away or increase when brought closer. (all your doing is using the magnetic field from the adapter to make the sensor work, don't worry about the cord)
Postmaster
Joined: Dec 2011
Posts: 3,860
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If you've got a few tools, one of these works just fine:
http://www.ebay.com/itm/Honeywell-Variable-Reluctance-Speed-Sensor-2874A003-Perkins-Engine-728062-02-New-/290943749708?pt=Motors_Car_Truck_Parts_Accessories&hash=item43bd994e4c&vxp=mtrYou have to press the original sensor out of the metal threaded ring, then turn/sand the outside of this new sensor down and glue it into place, but it works great if you do so, and is one heck of a lot cheaper.
I even wrote up a topic on this swap, somewhere.
http://www.ebay.com/itm/Honeywell-Variable-Reluctance-Speed-Sensor-2874A003-Perkins-Engine-728062-02-New-/290943749708?pt=Motors_Car_Truck_Parts_Accessories&hash=item43bd994e4c&vxp=mtrYou have to press the original sensor out of the metal threaded ring, then turn/sand the outside of this new sensor down and glue it into place, but it works great if you do so, and is one heck of a lot cheaper.
I even wrote up a topic on this swap, somewhere.
Mountain Pass
Joined: May 2012
Posts: 215
Likes: 0
I found an easy way of testing the tach sensor (well any magnetic pickup sensor) pull the sensor out of the truck and take your multi meter and set it to AC volts (low range) and probe the socket, then find one of those heavier wall adapters
and place the pickup end against it and you'll get a reading that will diminish when you pull it farther away or increase when brought closer. (all your doing is using the magnetic field from the adapter to make the sensor work, don't worry about the cord)
and place the pickup end against it and you'll get a reading that will diminish when you pull it farther away or increase when brought closer. (all your doing is using the magnetic field from the adapter to make the sensor work, don't worry about the cord)
My tach is not working so I did this test, I also checked the ohms on the sensor away from any metal and got a reading of 2,460 ohms. setting the meter on ACV and putting the sensor up to the wall adapter I would get a reading that would diminish as I pulled the sensor away from the wall adapter.
I only thought to test it after swapping it out with the sensor from another truck, I figured surely both of these sensors aren't bad.
so I read up on all the tach threads and here is what I came up with:
Test TPS/FIPS is in spec
Check your body ground wires near the ABS module which might be your problem as well...
Check the drivers side "inner" fenderwell first, and all the grounds around any electrical components in that area as well as body grounds.
I think I also seen a post that said to check the power distribution box for bad fuses/relays, my fuses all look good there.
going to clean up my grounds and then look for the procedure for the FIPS
Fleet Mechanic
Joined: Aug 2011
Posts: 1,570
Likes: 258
Checking grounds and fuses is a good start, the FIPS/TPS wont effect the tach, the tach does run through the TECA(computer) and then to the tach its self, so if you have blown fuses youll get no tach out put and the truck should be shifting like crap.
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