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 Post subject: Re: 3cyl. Tach !
PostPosted: Sun Nov 06, 2011 2:29 pm 
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doesn't the coil saturate with 12 volts and then get dumped to ground to discharge the coil's secondary?

you'd get a little added bump from the inductor absorbing the magnetic field as it collapses.

from trying to get the dash tachometer to work with a 12 volt pulse from my megasquirt controller i know that you can't make it happen unless you use a relay coil to get that little extra bump. 12 volts alone won't trigger the tach.

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 Post subject: Re: 3cyl. Tach !
PostPosted: Sun Nov 06, 2011 3:33 pm 
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Location: Southern California
Yeah, though without scoping that line, it's hard to know how big that signal should be.

I've just tried to duplicate JBs setup and can't get the tach to respond. I only have one, and don't want to take the risk of blowing it up, so I think I am going to wait for his resistor value suggestion.

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 Post subject: Re: 3cyl. Tach !
PostPosted: Mon Nov 14, 2011 1:01 am 
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Sorry for the delay - work and life and laziness got in the way.


Your two resistors, 27K and 9.1K in parallel gives 6.806K.

In a previous post, a tach went from 4 cyl and 6.25K to 3 cyl and 11.49K, or 1.838x

Using the same scaling will get you pretty darn close I expect.

so 6.806K x 1.838 = 12.5K total.

There isn't a standard 5% 12.5K resistor, but there is a 12.4K 1% you could use instead of your 27K and 9.1K resistor, OR, lift one leg of the 9.1K resistor and tack a 24K 5% across the existing 27K resistor. This would give you 12.7K, close enough.

Use a pulse generator like my setup to check your work.

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 Post subject: Re: 3cyl. Tach !
PostPosted: Tue May 08, 2012 8:47 pm 
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Got sidetracked for awhile but am about ready to get back into this. I'll try your values, JBD, thank you.

But I recall that I wasn't able to get my tach to respond using your setup and I didn't want to risk damaging mine. Can you please go over your connections, signal source and characteristics?

Thanks.

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 Post subject: Re: 3cyl. Tach !
PostPosted: Wed May 09, 2012 11:06 pm 
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Location: Laval,Qc
Well, I found a 3cyl W/Tach Speedometer since I've screwed my 4cyl. lol anyway I was about to use the Resistor's but finally found a vert with a cluster, paid 25$ !

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 Post subject: Re: 3cyl. Tach !
PostPosted: Mon Jul 09, 2012 6:32 pm 
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Location: Southern California
I never could duplicate the test setup, so I decided to gamble.

Got her done. Took an ugly instrument cluster with a severely damaged clear panel (got it very inexpensively), cleaned it inside and out, sanded and polished the clear to perfection, changed the resistors to a 12.4K (two 6.2K parts in series) part and stuck it in. Turns out that I did not have to lower the steering column to accomplish this. I did run into one issue, and that was the length of the speedometer cable. The original speedo is in the center of the cluster, and the new one is a few inches to the left. That matters with the original routing- too tight. Of course, I found this out AFTER everything was installed and I was attempting to hook the cable back up to the transmission. I rerouted the cable and all is well.

Image

Beauty!

Works perfectly. Turns out that the ratio of 1.838 is correct. So take your 4 cyl tach, determine what the original resistance value is, multiply that by 1.838 and install the new value. Then stick the cluster in your 3-banger and off you go.

Thanks for the help. Cheers!

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 Post subject: Re: Re:
PostPosted: Tue Apr 29, 2014 7:26 pm 
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Location: Calgary, Alberta
Peenutzz wrote:

Well, today I was bored, and I took another look at the cluster and I decided to give it a go, and try the trim-resistor. I connected the cluster to the car and fired it up. Checked all the lights, and they worked like they are supposed to. As expected, the tach pointed 3/4 from what it should. I took the car for a spin to warm up the engine and went back home. Took a look at the tach and at idle it was around 750rpm. Then I took it apart, and turned the trim-resistor clockwise all the way, which is about 180 degrees from the factory setting. Installed the cluster again, fired up the engine and a smile appeared on my face. At idle, the tach pointed about 2200rpm. I took it apart again, and since I turned 180 degrees, which meant roughly 1500 rpm more on the gauge, I turned the resistor back to factory, and then roughly 30 degrees clockwise again, so the gauge would point 1500/6=250rpm's more at idle. Installed it, and fired up for the third time. I was only a 100 rpm's off. :) I revved the engine up, and the rev limiter kicked in at about 6300rpm. Since it should be at 6500, and idle was a little low, I took the cluster apart one more time, gave the resistor a few more degrees and when I put it together for the last time, I checked and idle now is at 1000rpm, rev limiter at 6500rpm. Seems pretty accurate to me :D :D :D

I don't know if this will work for other clusters, since the pictures I've seen were totally different from the one I have here. So to make things clear: This cluster is one from a 1991 Suzuki Swift 1.3GS, which I fitted in a 1991 Suzuki Swift 1.0GA.


I have the same cluster but out of an 89 swift GS. I swapped a turbo 3 into mine and this tach adjustment worked perfectly. It actually has so much adjustment, you could probably run anything from a single cylinder to a six cylinder off of it. Don't quote me on that but I would bet that at very least it would do 2-5 cyls.
Thanks Peenutzz, I obviously didn't look close enough the first time I opened this cluster!

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 Post subject: Re: 3cyl. Tach !
PostPosted: Tue Apr 29, 2014 11:01 pm 
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Location: walsh,alberta,canada
did the resistor mod,changed the tach from a 4 cyl to a 3 cyl.
but now my engine (tach) redline/rev limiter is 4500 rpm
idle is 900~1200 depending on temp.
did I install wrong resistor? cant find the photos I took of mod.

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