Adapting an OEM Tach to Diesel

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cody c said:
I was looking at grabbing a abs sensor today. The parts guy at NAPA said that most ABS sensors use hall-effect versus being magnetic pickups. I am wondering what year the ABS sensor off of the exploder, or part # for the one you have used. Or if anyone else has a part # or more info on one that should work.

Unfortunately I dont have any fzj-80 ABS sensors around to test, and the NAPA here doesnt deal much with newer 80 series parts.

I would guess it is the same style tach sender for the fj80 3FE as a fj62? Anyone know?

Thanks,
Cody.
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All of the abs sensors that I've seen are magnetic type but then I generally deal with old junk ;)

I would still guess that most abs wheel sensors are magnetic because a hall-effect sensor will require an amplifier built into the sensor and I'm not sure if a solid state amplifier would be able to tolerate the temperatures that are likely to exist in the vicinity of the brakes.

A good way to differentiate a magnetic sensor from a hall-effect sensor is by the number of wires - hall-effect has three, a magnetic has two.

When I was first playing around developing this setup, I tried a bunch of different abs sensors that I had kicking around. They all worked fine. I only selected the FJZ80 sensor because it had the best physical configuration for my mounting location.

I think your best source for these would be a junk yard. It is an items I'm sure they rarely sell so you should be able to pick them up for next to nothing whereas a dealer will charge you an arm and a leg!
 
Thanks, I will try and source one here when I have some time, maybe this weekend.

Also, is there any problems with attaching 3 magnets as opposed to cutting three notches,? I guess I shoulda mentioned this in the last post.

Cody.
 
cody c said:
Thanks, I will try and source one here when I have some time, maybe this weekend.

Also, is there any problems with attaching 3 magnets as opposed to cutting three notches,? I guess I shoulda mentioned this in the last post.

Cody.
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The magnet is built into the sensor so there is no need to add magnets. Since all you are trying to do is disrupt the magnetic field three time per revolution of the crank (to match the 6-cyl engine that the tach is set up for), you can do it with either three notches, holes, or protrusions such as small block of metal or a bolt head mounted to your crank/pulley/flywheel.
 
I found one from a sunfire today, now i got to epoxy a couple pieces of metal to the harmonic balancer and make a bracket to support the abs sensor, and find what wire from the original tach comes through the firewall for the original sender. I tested it with some wire and a spare instrument panel I had, and with a drill and a large drill bit, seems to work once I get the right gap.

Thanks so much for posting this, much cheaper than doing the dakota digital thing, and I can use my stock tach!
 
cody c said:
I found one from a sunfire today, now i got to epoxy a couple pieces of metal to the harmonic balancer and make a bracket to support the abs sensor, and find what wire from the original tach comes through the firewall for the original sender. I tested it with some wire and a spare instrument panel I had, and with a drill and a large drill bit, seems to work once I get the right gap.

Thanks so much for posting this, much cheaper than doing the dakota digital thing, and I can use my stock tach!
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You need three pieces of metal added to the harmonic balancer to simulate the 6-cylinder engine that your tach is calibrated for. Are you at all concerned about epoxied pieces metal flying off?

The tach signal usually comes from the igniter so the wire that you're looking for should be in the vicinity of where the former igniter was mounted.

You want to keep the gap as small as practical. If it doesn't work at first, try reversing the leads from the sensor.

Once you get it working, post up some photos.
 
Im not too worried about little bits of metal coming off the balancer, I will have to dig through the wiring or electrical diagrams to find the wire, it was mostly chopped just inside the engine compartment near the firewall, so I will have to hunt a bit. I already used a large drill bit on the spare tach I have to replicate a tach signal, works well, I just got to find time to build a bracket and find some wires.

Ill post pics but not for a while when I can find some time.
 
Alright, I got a abs sensor on it and connected to a tach, but it reads right at idle then drops to 0 when I give it some throttle. I have just made notches on the balancer and mounted the sender on a bracket very close to the balancer.

I figured I would revive the thread instead of starting a new one, any suggestiions? How big of a notch do I need?

Thanks!

Edit: wider notches, works well!
 
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clean solution
 
cody c said:
Alright, I got a abs sensor on it and connected to a tach, but it reads right at idle then drops to 0 when I give it some throttle. I have just made notches on the balancer and mounted the sender on a bracket very close to the balancer.

I figured I would revive the thread instead of starting a new one, any suggestiions? How big of a notch do I need?

Thanks!

Edit: wider notches, works well!
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Glad you got it working! Just for reference, what make/model/year of vehicle did your abs sensor come from? How deep and wide were the notches that you cut into your harmonic balancer? What diameter is your harmonic balancer? How big was the gap between the abs sensor and the harmonic balancer?

This info would be good for others who might want to try this approach.
 
astr said:
Glad you got it working! Just for reference, what make/model/year of vehicle did your abs sensor come from? How deep and wide were the notches that you cut into your harmonic balancer? What diameter is your harmonic balancer? How big was the gap between the abs sensor and the harmonic balancer?

This info would be good for others who might want to try this approach.
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The ABS sensor was for a sunfire, (sorry forget the year, late 90's)
I built a bracket out of checker plate alloy to support the sensor, the gap between it and the harmonic balancer was about <1/8"
I ended up using a 3/8" drill bit to get a decent gap, it seems the width of the gap is more important than depth, I went about 1/8" deep at the shallowest (sides of the hole, center about 1/4" deep. Balancer is 26" in circumference.

Works well, most of the work was designing and building the bracket, and finding and running the wires from the tach.
:cheers:
 
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Just found this thread. Great work guys.:clap: saves everyone time and aggravation trying to source overpriced aftermarket junk.

I am going with the abs to harmonic balancer setup on my 60. Does it matter if the notches are perfectly spaced around the perimeter of the balancer to get a correct reading? My balancer has 2 notches that were already there from a crankshaft position sensor. I think that sensor will not work with the stock tach because it is a 3 wire setup.

By the way this is on a 6bt that is going into my 60 and I am trying to get everything mapped out before I yank the old 2f.
 
Spacing probably won't be critical from the electrical perspective but having three notches with 90* spacing could affect balance. Probably not noticeable on a 6bt :D
 
Thanks astr. I was looking at replacing the harmonic balancer anyway. Mine has a couple of chunks out of the rubber. NAPA has the cheapest oem replacement and I am going to see if it comes pre-notched for the dodge crankshaft sensor. if not I will be able to mill in three evenly spaced notches and that should work.
 
Update

I've been revving my 4HE1 a bit and noticed that around 2,500 rpm, the tach would drop back down to zero. As the rpms dropped below 2,500, the tach needle would pop back up. At first I thought that I had a loose connection but no such luck. I concluded that the notches that I had cut into the circumference of the flywheel were too narrow so that at higher rpm the pulse generated by the ABS sensor was too short and was being filtered out by the tach. The proper way to fix the problem would have been to widen the flywheel notches but that required pulling the transmission. Instead, I decided to tweak the tach circuit.

The tach input circuit is designed to filter the signal that originally came from the ignition coil. By reducing the size of the capacitors in the filter circuit, shorter pulses will get through. On the tach circuit board behind the meter movement are two capacitors labeled C473. They are 473 pF in value so I replaced them with 220 pF. Bingo! Tach now reads up to 3,400 rpm, the limit imposed by the governor. The photo shows the two capacitors that I changed.

I didn't try it but removing the two 473 pF capacitors may work just as well and would be a heck of a lot easier.

In retrospect, the three 0.75" notches that I machined into the flywheel circumference only represent 1.5% each of the total circumference of the flywheel. Next time I have the transmission out, I will widen them to 2.5" or 5% of the total circumference.
Tach-Caps.webp
 
astr said:
I didn't try it but removing the two 473 pF capacitors may work just as well and would be a heck of a lot easier.
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damn dude .. that's NASA science to me .. ! :frown:
 
Thanks Andy!

That is just the info I needed. Mine cuts out at about 2000 and I had just about given up and gone to a aftermarket tach out of frustration.
I'm going to try just removing them first and see what that does. I have a spare tach and so I can do some experimenting on that one. If not I will get a couple of new capacitors and solder them in.

Thanks a lot for posting this!

Don
 
3bjeep said:
What exactly do you do in the "real world" Astr? You come up with some impressive solutions!
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Are you suggesting that this is not the "real world"? :grinpimp::grinpimp:

I've run a software company for the past 25 years but my training is in electrical and computer engineering.
 
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