Tach sensor placement??
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Senior User
Joined: May 2010
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From: Oregon
Tach sensor placement??
I went to ford stealership and got a new tach sensor, mine works maybe 5% of the time... I checked the injection pump gear housing and its got a plug not a sensor in, where the ---- else could it be?
Not sure if a bump in the road brings it back temporarily or what... usually at 0, sometimes it'll go to 1k rpm, down as i slow down to like 500, and eventually 0 out again. once it went higher..
bad wiring or bad sensor? 75$ is painful but i can take it back if something else is the problem. I dont know where else it could be. T19 tranny if it matters
Not sure if a bump in the road brings it back temporarily or what... usually at 0, sometimes it'll go to 1k rpm, down as i slow down to like 500, and eventually 0 out again. once it went higher..
bad wiring or bad sensor? 75$ is painful but i can take it back if something else is the problem. I dont know where else it could be. T19 tranny if it matters
Lead Driver
Joined: Mar 2006
Posts: 5,111
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From: western SD
Sounds like you have an aftermarket tach. Look on the harmonic balancer for a magnet glued on it.The sensor then reads the pluses from the magnet as the motor turns. I have also seen tachs that run off the alternator on some dirt equipment, but have no clue how they work.
Lead Driver
Joined: Dec 2006
Posts: 6,496
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From: So. Jersey
The stock tach sensor is next to the oil fill, the large nut with 2 black wires coming out of it. If you have a factory tach (in the dash) you should have a black plug for the sensor to plug into. If you have some after market tach, it may use a "flying magnet" style pick-up or getting a signal from the alternator.
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Senior User
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From: Oregon
thanks crew, i knew that is where the stock tach sensor goes but mines the plug like you find on non-tached idis.... But I have the tach gauge cluster... I'm not the original owner and this isn't the original engine although this was a 6.9 diesel when it was made. Been working alot of kinks out and this is one 
Alternator is just a normal alternator that i replaced since the old one gave out when I got the truck. Upgraded to 130amp 3G alt instead of the stock alt. voltage sensing for the charging and positive cable being the only things coming into and leaving the alt
Guess I'll look on the crankshat pulley for a magnet sensor? Or am I misunderstanding?
Thanks for the help so far. Guess I can get my 75$ back from ford since I have an aftermarket. I wanted to see if there was another sensor possibility like flywheel... but ya both confirmed my suspicions that they only did it off the IP gear
Alternator is just a normal alternator that i replaced since the old one gave out when I got the truck. Upgraded to 130amp 3G alt instead of the stock alt. voltage sensing for the charging and positive cable being the only things coming into and leaving the alt
Guess I'll look on the crankshat pulley for a magnet sensor? Or am I misunderstanding?
Thanks for the help so far. Guess I can get my 75$ back from ford since I have an aftermarket. I wanted to see if there was another sensor possibility like flywheel... but ya both confirmed my suspicions that they only did it off the IP gear
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Senior User
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From: Oregon
No magnet on harmonic balancer, nor any cables in the area.
Have the gauge cluster almost out but which connections do I undo t o get it out, i dont have enough slack to get the back of it to trace where it goes to. Do i need to mess with the giant bundle of wires near the pedals? I found the speedo cable I am pretty sure. Its a fat grey line that runs parallel to the fuel pedal right? Goes to the tranny? Or is that my taco-meter cable? I played ith it some and it makes a noise in the gauge cluster so i know its tach or speedo... played with it running and tach didnt move though.
Have the gauge cluster almost out but which connections do I undo t o get it out, i dont have enough slack to get the back of it to trace where it goes to. Do i need to mess with the giant bundle of wires near the pedals? I found the speedo cable I am pretty sure. Its a fat grey line that runs parallel to the fuel pedal right? Goes to the tranny? Or is that my taco-meter cable? I played ith it some and it makes a noise in the gauge cluster so i know its tach or speedo... played with it running and tach didnt move though.
Methanoholic
Joined: Mar 2009
Posts: 6,442
Likes: 8
From: Maine (NorCal Native)
87Crew ...
What paint and color did you use on that motor ???
All I can find is the "New Ford Grey" and it is way to light, I like the darker Grey like you used.
Thanks
-Enjoy
fh : )_~
What paint and color did you use on that motor ???
All I can find is the "New Ford Grey" and it is way to light, I like the darker Grey like you used.
Thanks
-Enjoy
fh : )_~
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
Do you have a connector out near the IP that the sensor you bought would plug into?
The stock sensor basically counts the IP drive gear teeth to give you a tach signal.
And that is the only gear that has the right number of teeth.
The stock sensor basically counts the IP drive gear teeth to give you a tach signal.
And that is the only gear that has the right number of teeth.
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Lead Driver
Joined: Dec 2006
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From: So. Jersey
For the tach, I bet whoever did the motor swap kept the "nontach" harness, that's why you have no plug.
Can anyone confirm that a nontach truck doesn't have the plug from the engine harness?
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Lead Driver
Joined: Dec 2006
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From: So. Jersey
The body harness I'm sure has the tach wires at the plug on the passenger fenderwell but stops there.
Probably will need to run 2 wires from the plug to the sensor or replace engine/alternator harness. .
Post Fiend
Joined: Nov 2003
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From: Nutter Fort, WV
The tach sensor wires are in the alternator harness, not the engine harness.
Wire cutters would be the only way they came off since there is no connector over on the passenger side inner fender for the tach wires, just the one at the IP that the sensor plugs into.
Wire cutters would be the only way they came off since there is no connector over on the passenger side inner fender for the tach wires, just the one at the IP that the sensor plugs into.
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Senior User
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From: Oregon
I'll take another look in the morning but I bet the harness was reused from a older motor. I thought it was registering but it might just be bouncing from vibration. i've seen it climb as high as 2500 rpm but usually only 1000, and then it stays at 0 most 95% of the time so i dont know if if actually lives or not.
Tomorrow morning I'll finish pulling the cluster out and follow the tach wires, if theres any attached to the gauge, and see where they go if anywhere
Tried contacting the prior owner but no luck 
Tomorrow morning I'll finish pulling the cluster out and follow the tach wires, if theres any attached to the gauge, and see where they go if anywhere
Tried contacting the prior owner but no luck
Lead Driver
Joined: Dec 2006
Posts: 6,496
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From: So. Jersey
The tach sensor wires are in the alternator harness, not the engine harness.
Wire cutters would be the only way they came off since there is no connector over on the passenger side inner fender for the tach wires, just the one at the IP that the sensor plugs into.
Wire cutters would be the only way they came off since there is no connector over on the passenger side inner fender for the tach wires, just the one at the IP that the sensor plugs into.
Again being an 87-up it has a plug (bricknose). I know because I just did the 3g swap and I unplugged the harness plug at the fender well that included the alt and tach harness for the engine (NO WIRE CUTTERS NEEDED). Its a typical round grey ford plug. If a picture is necessary I'll capture it.
Maybe they did it different on your truck Dave but as you recall there were multiple changes in 87-up bricknose trucks.
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Senior User
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From: Oregon
Sorry for the long lapse in time, was looking for this thread and have come back with my results thus far...
You were right, I found it tucked in the passenger side battery area dirty as heck... I installed the new from ford tach sensor and hooked it up..
It will read now but its way too low - like if i rev it hard it barely hits 1500 or 500 i forget whhich but you can tell it responds to throttle I made sure. idle is reading 0.
Could it be the wrong dash cluster, the rpm limit is only4k though so it must be a diesel right??
My alternator harness was chopped up when i bought it, more-so after i installed a 3g alternator. I found the tach connector, i followed the line to another connector.... at first it has two wires like the tach sensor wiring, then at the second connector a third wire shows up. is this the right one?
I also found a odd looking ground/black wire that goes into the thick bundle of wiring that goes across the front end, tried putting it to ground but nothing changed, then it accidentally slung over to hot and sparked but I thought this was the end that got grounded?
I used a volt meter to probe the wiring, anything in perticular i should look for??
I can take pictures if needed.
thanks again
It will read now but its way too low - like if i rev it hard it barely hits 1500 or 500 i forget whhich but you can tell it responds to throttle I made sure. idle is reading 0.
Could it be the wrong dash cluster, the rpm limit is only4k though so it must be a diesel right??
The tach sensor wires are in the alternator harness, not the engine harness.
Wire cutters would be the only way they came off since there is no connector over on the passenger side inner fender for the tach wires, just the one at the IP that the sensor plugs into.
Wire cutters would be the only way they came off since there is no connector over on the passenger side inner fender for the tach wires, just the one at the IP that the sensor plugs into.
I also found a odd looking ground/black wire that goes into the thick bundle of wiring that goes across the front end, tried putting it to ground but nothing changed, then it accidentally slung over to hot and sparked but I thought this was the end that got grounded?
I used a volt meter to probe the wiring, anything in perticular i should look for??
I can take pictures if needed.
thanks again