Everyone knows about the problem with the Tachometer sensor: It's a ford-specific part, and expensive($60, or so I hear). Well, I went the DIY route, and so can you.
The tachometer sender is a standard VRS(Variable Reluctance Sensor), so you just need to find one which will work, and will fit.
Here is what I found: Honeywell Variable Reluctance Speed Sensor 2874A003 Perkins Engine 728062-02 New. This guy's been selling them for ages, plenty left.

Anyway, once you have your new sensor, the first thing to do is remove your old sensor. The old sensor is comprised of two components: The sensor itself, and the threaded metal piece. They are glued together.

The first thing to do is to separate the two components. I suggest using an arbor press, if you have it available:


Now, remove any excess stuff from your new sensor. In the case of the Honeywell one that I'm using, there's a metal ring that needs to be removed. Just twist the ends of the tabs to free it(pair of pliers/multi-tool).

I also needed to remove the "hood" around the two connection pins, as I don't have a proper plug for this sensor. You may or may not need to do this. I used a $20 harbor freight air die grinder/3" cutoff tool to do this.


Now, check the diameter of your newly trimmed sensor. If it's too large to fit inside the metal sleeve, you will need to turn down the diameter. For the honeywell ones, it was about .07" too large, so I stuck the end in my lathe and turned the rest down with a HSS partoff tool(due to it being square; needed more clearance than my left/right-handed bits had. I used it in proper partoff tool method, plunging in X, shifting, plunging)


Now, check that it fits. You want it relatively tight, it should fit snugly but not require a lot of force to get in or out:


Now, stick a couple of drops of super glue(Cyanoacrylate) into the inside of the metal sleeve, and slide the sensor in. You want the end of the sensor flush with the end of the sleeve:



Wait a few seconds for it to dry, then tip it up on end, and add super glue around the end, where the chamfered edge of the metal sleeve meets the end of the sensor. Just pour a bit in there, let it dry. I've done it several times on mine; the more glue the better:


Now, on the top end, you'll want to pour a layer of JB weld. This is mainly to prevent any leaks, as well as make things even more solid. I actually did this after running it for a while on my first one - I hadn't done this, or put a good layer of glue on the bottom, and got a minor oil leak through it.


Now, solder up those connections. In the Honeywell sensor, they're easily tinned, quite nice to solder on:


And finally, protect those connections. I melted a bunch of hot glue over the solder to protect it and prevent accidental grounding of the connections(see second to last pic).


Finally, install it! Connect your two wires up to the two that go to the original sensor(orientation doesn't matter; it's AC output), and go for a test drive!

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Having done this myself, I've found that I get a nice consistent reading across the scale, versus a reading that would vary based on temperature and sometimes zero out at idle. On my truck, it seems to be about 100 RPM off(reading 1700 when it should be around 1600 or so), but that's easily due to my gauge being old and such. We'll see how accurate it is once I hook up an Arduino and a VRS interfacing chip.


I hope this guide helps some people, though if you guys know of a "backwoods" method to turn down a cylinder using a drillpress or something, post it. I'm lucky in just being able to go to my shop and stick it in my lathe, and I know most of you won't be that lucky.


Good luck!

 

nice write up!.....think ill just pay the stealership price tho lol

 

hmmm...for dollers i migh as hell give it a try

 

sweet! Think I'll try this.
My tach has been pretty much dead for over a year and it would be nice to fix it without spending an arm and a leg.

 

you must really be pinching pennies to save $50 and put all that labor into it lol.

 

lol when your poor like me, you gotta do what you gotta do.. i got a lathe, som free time eery once n a great while when im notworking...what i dont hae is an extra 70 dollers laying around

 

I found this one awhile back...

That expensive Tach Sensor - Diesel Forum - TheDieselStop.com

 

I was waiting for someone to do this for some time now

Does this work well enough for an E4OD equipped truck?

If so I'd say its a good option. If nothing else it means we can still keep these trucks running long after the tach sensor is declared "obsolete".

 

sounds to me like you're equipment rich and cash poor!

for not having a lathe myself, i would have rigged it up in the drill press, where i've turned down a number of parts. sometimes i use a file, sometimes a dremel with a cutoff wheel, whatever the job requires. turning parts in a drill press isn't much different than in a lathe, except that you have to figure out how to hold the tool freehand

 

Well, aside from the equipment costs, the actual time it took me to figure out and make my first sensor was under an hour. Second one about half that, and most of that time is setup. If I had a bunch to do, I figure about 5 minutes each in actual work time.
But yes, I am equipment rich, cash poor - I've got a decent shop setup, but I'd never be able to justify $70 - easily half of my discretionary budget - for a practically useless tach sensor. But DIYing it? Fun, and for $8 in parts? Yeah.

As far as working well enough for an E4OD? I don't know. Mine's a stick. But, I have to say it seems very repeatable and consistent across the speed range.

Y'know, if you guys need, I suppose I could probably make a few to sell; I'd just need the steel sleeve/ring piece. That and $25+shipping, and I could make you one.

Josh, can you put a decent explanation of a good way to hold a toolbit for drillpress-lathe work? Like, some way to keep it consistent?

 

well being consistent is the hard part, its more like cut a little, stop and measure, cut a little more, repeat. but then i've done a good bit of redneck machining on various parts. mounting the work in the chuck is easy (if the chuck is big enough), sometimes a tool can be mounted the the crossvise on the drill's table, other times creative methods must be employed. for this job, i'd likely hold a coarse file against it while spinning, and stop to clean the file with a wire brush as needed.

 

deviating off course a little bit, but my tach stopped working when i took the auto out in favor of manual. Ran thru TCM im assuming. Do i simply trace the wires from sensor to PCM, and route them directly to wires going to tach?

 

What a co-inka-dink!!!...I just bought a tach sensor from the stealership for $75 bucks. Installed it and my tach works like new. Anyway, since I am slowly but surely restoring my 86 F250 4WD 6.9, I bought 2 of those VSR's from the e-bay link.

I am going to set one up and use it in the place of the one I bought fron Ford and sock it and the other e-bay one away for just in case type thing.

I will certainly post the results here when I compare the Ford sensor to the homemade one as far as accuracy is concerned. I hope all this works.

 

I just bought one too. Sure as hell can't afford the Ford one, I'm wondering if I have a ground issue somewhere in the dash too, but thats another story.

When I get it working, I'll try and compare the reading from the dash tach to the one on my timing meter.

 

Got my VSR's yesterday. The one for $7.99 on ebay. Well I took my old stock sensor that I replaced with new stealership one. Did the mods and installed it and it seems to work fine...steady as a rock. Accuracy may or not be perfect, but it is certainly close. Now I have 3 good tach sensors.