The silly thing on my 2.8 appears to be on its way out, so I was planning on building one using this from Oliver Scholz's web site.

Then I found this thread in the archives, which suggests that the schematic on Oliver's web site is for the L4 & that the V6's tach filter is different.

Rodney's replacement tach filter claims to work for either motor. ²

So which is it--does one size fit all, or are they different for each engine?

If they are different for each engine, does anyone have the schematic for the V6 tach filter?

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his: 1985 2M6 SE
mostly stock, but becoming more my creation than GM's with each passing day

hers: 1984 2M4
upgrade to 86 wiring, Duke, and Isuzu in progress

I do know they ARE different:

1. I baked up a new filter according to the schematics in your post: IT DOESN'T WORK in my V-6
2. My V-6 filter needed to be replaced, because the wire broke off right at the filter. I cannot measure ANY resistance thru the old (working!) filter!

I'm curious about the answer to this...

Pssssst... Cliff, if you're watching, did you ever dissect a V6 tach filter like you said you would in that archived thead?

Here's a tach filter using the values shown at http://www.thefieroclub.com/osg/takfiltr.htm

It's a low pass filter (edit:see below) and should keep RFI out of the radio.

[This message has been edited by spark1 (edited 11-13-2004).]

Thanks spark1. Seems that I gave you a positive rating a while back for a variety of electrical info.

Has anyone tried using the components listed in the OSG (spark1's reference above) with success (or failure)?

And is it confirmed it works in a V6?

Can anyone else try to measure the resistance of a (working) V6 tach filter?
That would clear up some of the confusion.

Yes, I did disassemble a tach filter once. There are actually 2 kinds in use for the V6. This is the preferred one:

The other type uses two 6k8 resistors instead of the 10K and 3k3. But the one shown above works better.

Cliff,

3k3 is 3300 ohms?
8n2 is 8200 pF?

Can you confirm (or anyone) that you cannot measure any resistance thru a good V6 tach filter?

I just tore apart an old V6 with working tach filter. I'll dig it out of the crap pile and put an ohm meter to it today at lunchtime.

3K3 is 3.3 K
8n2 is 8.2 nF

[This message has been edited by spark1 (edited 11-11-2004).]

quote Originally posted by Cliff Pennock: Yes, I did disassemble a tach filter once. There are actually 2 kinds in use for the V6. This is the preferred one: The other type uses two 6k8 resistors instead of the 10K and 3k3. But the one shown above works better.

The difference between the one with the 6.8K resistors and the one with 10K reistors are:

6.8K circuit has a cutoff frequency of 1011Hz
10K circuit has a cutoff frequency of 852Hz

quote Originally posted by spark1: Here's a tach filter using the values shown at http://www.thefieroclub.com/osg/takfiltr.htm It's a low pass filter (about 23 kHz) and should keep RFI out of the radio.

Actually according to the values you have shown the cutoff frequency is 3.696KHz (23K radians/second)

By the way, the original circuit posted in this thread has a cutoff frequency of 1.074Khz. So it seems that if the 3.696Khz and the 852Hz circuits work, then any of the circuits posted should work. I hope this helps

I would post the pictures of the analysis, but I don't know where to post the pictures.

[This message has been edited by cyrus88 (edited 11-12-2004).]

Thanks for the correction. Ran the numbers through an online calculator and your results are right.

If you want to post pictures just click on the at the bottom of this page and follow the instructions. This is a screen print I took of the filter calculator and cleaned up a little using MS Paint. Then used IrfanView to to convert it to JPG for posting. Real easy.

[This message has been edited by spark1 (edited 11-13-2004).]

Hey spark1,

I can't use the PIP because I run a Linux machine. What you have posted is fine for now.

Just in case anyone wanted to know, the "cutoff" or "corner" frequency for a capacitor and resistor setup is:

cutoff-frequency=1/(2*pi*R*C). If you prefer radians/second then cutoff-omega=1/(R*C).

Just my 2-cents.

quote Originally posted by cyrus88: By the way, the original circuit posted in this thread has a cutoff frequency of 1.074Khz. So it seems that if the 3.696Khz and the 852Hz circuits work, then any of the circuits posted should work.

Not really, all the others are first-order filters (which is the reason they don't work as well) while the one I posted is a second-order filter.

Not that I really know what all that means, just that a second-order filter works much better than a first-order filter - which BTW, I tested to be true)

Hi Cliff,

I agree that your filter has a sharper drop off beyond the cutoff frequency, but what I was trying to say is that if the higher frequency filters work, then so should the lower frequency ones, whether they are second order or first.
Second order means that there are two energy storage devices in the circuit which yield a second order differential equation. So, for the circuit you have shown there are two capacitors, which provide a transfer function:

Vout/Vin=1/[R1*R2*(s*C)^2 + (R2+2*R1)*s*C + 1], which has a second order pole.

R1=10k, R2=3.3k

[This message has been edited by cyrus88 (edited 11-13-2004).]

I have no idea what you just said.

so will someone make one of these? lol post pics and tell me where/what you bought?

i need to do this also and i really can't afford to fork out a whole lotta money for a new one

Thanks, Travis

I got a new tack filter from Rodney's and it works, but someone there took my credit card no. and started charging stuff over in thier state.
My credit card company called me about these charge's. End of story, had to get a new charge card.

I now made the one Cliff posted and it works perfectly well on my V6 Formula!
Thanks!

[QUOTE]I got a new tack filter from Rodney's and it works, but someone there took my credit card no. and started charging stuff over in thier state.
My credit card company called me about these charge's. End of story, had to get a new charge card.[/QOUTE]

alienfiero;

This is the second time you tell this story. I will report this now to my credit card merchant services and let them deal with you. I never give anyones card number out nor has anyone contacted me on any unusual credit card activity. Even you never contacted me. You only insist on posting this on a public forum. If your number was stolen it was not from me. If you have proof please send anything you have to me. I asked this the last time you posted this and I have yet to recieve any info. Why do you insist on bashing me when you have no proof I was involved? What is YOUR problem? Please let me know. Popting this to a public forum when you have no proof I was involved is very illeagal and you can be taken to court if you persist on posting this.

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PLEASE NOTE MY NEW ADDRESS

Rodney Dickman's Fiero accessories
7604 Treeview Drive
Caledonia, WI 53108
(262) 835-9575

www.rodneydickman.com

quote Originally posted by joeformula88: I now made the one Cliff posted and it works perfectly well on my V6 Formula!

Good to know, Joe. Thanks!

I never did get to trying this out myself before parking my toy for the season, but I will have it done for the next!

alienfiero;

I searched all my records and I can't find anyone in Auburn, WA that bought a tach filter. Can you send me some info on that? Or are you just trying to cause a problem?? I see you have a lot of - ratings. What is YOUR problem? I emailed you a few times asking for info the last time you posted this and I have not received anything. Why? Please answer me.

------------------
PLEASE NOTE MY NEW ADDRESS

Rodney Dickman's Fiero accessories
7604 Treeview Drive
Caledonia, WI 53108
(262) 835-9575

www.rodneydickman.com