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Factory tach with KA24DE swap


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Well, that's where it gets tricky, lol. I've been working on this myself for some time, and keep running in to dead ends all over. S13's are no problem, because they use the same type of tach signal output as every other motor in the world, but the s14 uses something different. The signal coming from the computer will not run any other tach, except an oem s14 one. (from what I've found so far anyway)

 

The options I've found so far are:

1) Buy a tach adapter (and cut up the motor harness) that uses the CAS (cam angle sensor), and converts it to a standard signal (about $100). Then change the board on the back of the 510 tach to a modern one, (not a feed through), so it uses the normal tach signal. (I updated my 510 tach, and it works great on any motor except the s14, lol)

2) Use an s14 oem tach and fab it to fit into the 510 housing and use the 510 face, so it looks just like the factory tach (but there are 2 different oem ones and you have to use the correct s14 tach)

3) Buy an aftermarket distributorless tach, (that also uses the CAS for the trigger) and cut it up to fit the 510 housing and gauge face.

 

I've talked to guys that have tried to use the coil negative (in the harness) for signal, (like you would on a normal motor), but it didn't work.

 

Please, someone chime in and tell me I'm crazy, and that there is a better (super simple) way to make it work, and that I wasted countless hours on tons of forums, and all the time wiring up all these tachs, just to find out nothing works, lol. (it would really make my day.). I have 2 of them to do myself right now.

 

Please, let's figure this out, it's been driving me crazy, lol.

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I thought the standard response for this was to wire in the tach the same as it is with the L16, which is in series with coil positive. I'm assuming you are using the series tach with the two white wires. If so, all it does is sense the current flow to the coil. As long as your KA still uses one coil and a distributor, you should be able to attach coil positive to one of the white wires, and the other white wire attaches in place of the original coil positive on the coil. If I am wrong, you could most likely find the answer in the "how to wire a KA into anything" thread.

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Yep, I assume that would be true with the s13 motor, but the s14 motor doesn't have an external coil. And for some reason, if you try to catch the feed for the coil in the harness itself , it still won't work. I even converted my 4 wire 510 tach to a 3 wire, and it works great on any motor, except an s14, lol.

 

 

Really? I've never tried running a factory tach through an S14 KA but I've done it on other motors with no problem. Are you sure you tapped into the right wire? Maybe there is other items that splice into the coil wire and power was being rerouted around your tach. It's been a while since I've wired an S14 ka and can't remember exactly how the coil/dizzy wiring is managed but it seems to me it should work.

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The S14 does not have an external coil, but it does have an internal coil.

If you look at the factory wiring diagram for the S14 240sx, you can find which wires are Coil + and Coil -.

In my 610, to get the factory tach to work, I had to wire it in series with the coil + wire. It works perfectly.

 

I guess my question was, do I do the same thing for the 510 factory tach?

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Yes, it would be the the 2 white wires (for the feed through loop) on the 510 tach. Please let me know if you get this working, because I've been trying to figure this out for a while. I'm going to kick myself it was really that simple, lol, (since that was the original first idea that I had to make it work.)

 

 

Really? I've never tried running a factory tach through an S14 KA but I've done it on other motors with no problem. Are you sure you tapped into the right wire? Maybe there is other items that splice into the coil wire and power was being rerouted around your tach. It's been a while since I've wired an S14 ka and can't remember exactly how the coil/dizzy wiring is managed but it seems to me it should work.

 

I haven't actually tried the feed through on my car yet, because I talked to others online that had, and they couldn't get it to work. I didn't want to cut into my harness, until I had a real definitive answer that it worked. (I knew I should have just tried it myself. That's what I get for listing to engineer type tweaks on the internet, I should have just gone with my backyard instincts, lol).

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Tach wire up: S14 KA24DE

On the front of the distributor is a 2-wire plug. This is the coil. One of those wires is black with red. Cut this wire, and connect in series with the tach. BAM!

It works.

 

By the way, the factory 510 tech responds really slowly to revs...30 year old technology right?

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I am hijacking my own thread:

Todd, I am going to order some stickers from you that I am going to use as stencils.

Going to put them on an anodized aluminum part, then bead blast the stencil, leaving bare aluminum. Poor-mans laser etching....

By the way here is a pic of the ones you did for the lotus:

forflickrdsc0272edit2.jpg

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  • 4 years later...

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