Guide: DIY Tachometer Sender
Logistics Pro
Joined: Sep 2007
Posts: 3,737
Likes: 179
From: Western Mass
Mine came in the other day, but haven't had a moment to do more than open the package. Still trying to finish my front brake job/axles/spring work that I started last week. Hope to be able to play with it this weekend or next week.
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Postmaster
Joined: Dec 2011
Posts: 3,860
Likes: 7
Cool, guys!
Speaking of grounding issues, it seems to be a common problem. I solved it by running extra ground leads from the alternator case to the cab sheet metal - used self-tapping screws to get a good contact - Seems to have solved a problem I had earlier with "pulsing" lights/varying charging voltage.
Tach sensor wise, it appears that one of the two wires can be grounded without issue; grounding one(black wire?) doesn't affect the signal, but grounding the other(green wire?) completely grounds out the signal.
This is good because now VRS-sensor chips are usable while the tach sensor is also connected to the original system - all the chips I've seen require one lead to be grounded.
If you're worried about ground issues, you can always try using a jumper wire; see if it helps.
Speaking of grounding issues, it seems to be a common problem. I solved it by running extra ground leads from the alternator case to the cab sheet metal - used self-tapping screws to get a good contact - Seems to have solved a problem I had earlier with "pulsing" lights/varying charging voltage.
Tach sensor wise, it appears that one of the two wires can be grounded without issue; grounding one(black wire?) doesn't affect the signal, but grounding the other(green wire?) completely grounds out the signal.
This is good because now VRS-sensor chips are usable while the tach sensor is also connected to the original system - all the chips I've seen require one lead to be grounded.
If you're worried about ground issues, you can always try using a jumper wire; see if it helps.
Laughing Gas
Joined: Jun 2007
Posts: 1,106
Likes: 35
From: Virginia
Yep, yep, yep; its time for some iced tea. I replaced my sender; got here in 2 days. The tach that was almost dead has stopped all together. I have not checked any other things I just did this mod first because the sensor was already leaking, yep, yep, yep. I'll check it either tomorrow or whenever. I never really drive my truck to any RPM limit anyway. It was actually easy to do. I used my bench grinder's wire wheel to take it down in diameter which left hundreds of little groves to hold the silicone, then I pressed it into the threaded fitting; no leaks, but the tach isnt working either.
Could the wire wheel have damaged the sensor?
UPDATE: my tach is sticking. I drove it today and it was sticking.
Could the wire wheel have damaged the sensor?
UPDATE: my tach is sticking. I drove it today and it was sticking.
Postmaster
Joined: Feb 2011
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Likes: 1
since your tach was on its way out to start with, did you do a full diagnosis to prove the sensor was your problem? possibly its the wiring or the gage.
if you have a friend with an IDI, you could swap sensors for a quick test and see if that changes anything. that'll at least point you in the right direction.
if you have a friend with an IDI, you could swap sensors for a quick test and see if that changes anything. that'll at least point you in the right direction.
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Postmaster
Joined: Dec 2011
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The other thing you can do is connect your multimeter to the two leads/pins of your new tach sensor. Set your meter to the AC range.
With the engine running,you should see /some/ voltage, and it should go up if you accelerate. If you see absolutely nothing, I'd say it's likely faulty. If your meter goes crazy and/or puts out random numbers, I'd say it's working - At 1000RPM, you should see somewhere around 900hz(at 106 gear teeth on the gear, which goes around once for each two engine revs), which is quite fast compared to the 60hz AC these things usually measure.
With the engine running,you should see /some/ voltage, and it should go up if you accelerate. If you see absolutely nothing, I'd say it's likely faulty. If your meter goes crazy and/or puts out random numbers, I'd say it's working - At 1000RPM, you should see somewhere around 900hz(at 106 gear teeth on the gear, which goes around once for each two engine revs), which is quite fast compared to the 60hz AC these things usually measure.
Laughing Gas
Joined: Jun 2007
Posts: 1,106
Likes: 35
From: Virginia
For those desiring to reduce the sensor diameter without a lathe
I am posting this for those, like me, without a lathe but wish to reduce the diameter of the sensor. 
I used a standard wire wheel on a bench grinder and it produced tiny grooves that would hold silicone and prevent leaking while using compression to keep the sensor stable. Then I added silicone and pressed the sensor in.
WARNING - If you go the wire wheel route make sure your diameter is not too large because you risk cracking the sensor. I used a drill press vise to hold the sensor safely 
.
I used a standard wire wheel on a bench grinder and it produced tiny grooves that would hold silicone and prevent leaking while using compression to keep the sensor stable. Then I added silicone and pressed the sensor in.
WARNING - If you go the wire wheel route make sure your diameter is not too large because you risk cracking the sensor
. I used a drill press vise to hold the sensor safely .
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Postmaster
Joined: Dec 2011
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I figure this topic deserves a status report. So far, so good. My tach sensor's working great, no issues with it. It's not leaking oil, and hasn't for over a year now(since I built one right, with plenty of JB weld), and the signal's good.
I've had a couple of issues with it flaking out in the past couple of months, and thought it was failing... Comes to find out, a loose piece of old wire(bailing wire it looks like) had somehow managed to lodge itself such that it was touching ground and the other end was caught just inside the plastic piece on a crimp connector... as I'd bounce around on the road, it'd alternately short out the signal and not. Removed it, rock solid.
I've had a couple of issues with it flaking out in the past couple of months, and thought it was failing... Comes to find out, a loose piece of old wire(bailing wire it looks like) had somehow managed to lodge itself such that it was touching ground and the other end was caught just inside the plastic piece on a crimp connector... as I'd bounce around on the road, it'd alternately short out the signal and not. Removed it, rock solid.
Logistics Pro
Joined: Sep 2007
Posts: 3,737
Likes: 179
From: Western Mass
I guess I'll post my results as well. Not sure when I actually put it together, but sometime last fall I think. If I remember, I used the grinding wheel on my bench grinder to roughly reduce the diameter, then smoothed and finished with a file. Didn't take that long at all. Covered it with JB weld and set it in place. Its been working great since then.
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Postmaster
Joined: Dec 2011
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Can someone update the link to the sensor in the first post to this please:
Honeywell Variable Reluctance Speed Sensor | eBay
The current link is broken, due to Ebay getting rid of old items.
Honeywell Variable Reluctance Speed Sensor | eBay
The current link is broken, due to Ebay getting rid of old items.
Mountain Pass
Joined: May 2012
Posts: 215
Likes: 0
wish I had room to do this mod or this one https://www.ford-trucks.com/forums/1...placement.html
working on a my new diesel and the tach is bad, but the vacuum pump is in the way, if only the hole for the tach sensor was in a different place on the injection pump cover.... maybe I could tap a new hole?
working on a my new diesel and the tach is bad, but the vacuum pump is in the way, if only the hole for the tach sensor was in a different place on the injection pump cover.... maybe I could tap a new hole?
Freshman User
Joined: Aug 2014
Posts: 20
Likes: 0
From: Huachuca City, Az.
Tach sending unit
I just did your homemade sending unit. Great idea! I just went to the local transmission shop and used the input turbine speed sensor from a newer version of the old A4LD I think it is a 5R 55. You just have to shave the mounting screw lug off and reduce the o ring grove to fit the old mounting bolt.. Super glue then epoxy the ends. Screw the housing in before you super glue it. That way you can point the wires in the right direction. The tach starts off at zero but then as soon as you touch the peddle it jumps into action. Seems to be accurate when working. Thanks for the input. Oh! That makes it a ford part. I saw one using a Cavalier sensor. hope this helps.
hope this helps.
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