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Tach Mod 4.9 - I did it wrong by arte444
Started on: 06-22-2013 12:25 AM
Replies: 20 (411 views)
Last post by: arte444 on 07-19-2013 01:36 PM
arte444
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06-22-2013 12:25 AM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

Trying to adapt my tachometer from my 88 4cyl to my 4.9. I bought a 200k pot and it immediately pegs the tachometer when it starts. The pot adjustment also does nothing. I'm thinking I might have it installed backwards if thats possible.

It has 3 pin outs and im using #1 & #2. It also seems to register at 200k best I can tell with my ohm meter.

These are the model numbers from the pot.

BORTUN
CW
3006P
204
0907T

I made sure I cut the trace as best as I could with an exact-o-knife.

I think this is the ebay page.
http://www.ebay.com/itm/3-x...&hash=item3cbb239e04

------------------
-Kyle
Email: kakagiraffe@gmail.com
1988 Notchback 4900SC 5spd Isuzu, Spec Stage 4
True Dual Exhaust, Delta Cam
1992 Honda Civic EX
2006 Pontiac G6 Ecotec

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phonedawgz
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06-22-2013 01:14 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post

Well the first problem is going to be that using Oliver's examples to start with you are going to need about 240K ohm of resistance. It will be hard to get that from a 0 - 200K adjustable pot. Since the ebay auction was for three, I assume you have extras?

So using two of the adjustable pots, solder a wire from pins 1 of one of the pots to pin 2 of the other. Now connect your ohm meter to the remaining pins 1 & 2 and pre-adjust the pots to get 240k ohms. You should have the right pins of the pots. When you daisy chain the two pots their resistance will add, and so what you should now have is something that could be adjusted from 0 ohms all the way up to 400 k ohms.

Note also the lower the resistance, the higher the tach will read. So with a 200 k ohm starting point, the tach should have been reading high.

idk why it didn't seem like the pot wasn't adjusting. Use your meter and try them out. Perhaps the one you started with is broke at 200 k ohms. That would still work since your second resistor could be adjusted to 40k ohms. Just look for 240 k ohms from end to end. Once you got it solder the two back to the tach and see where you are at.

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Arns85GT
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06-22-2013 08:25 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

I did my v6 tach the other way by replacing the capacitor. The proper value is .00068f but I couldn't get the right value at my supplier so I used a .00064f and it is within 200 rpm, not perfect but close. I may still put in the rheostat. I have both 250 and 500k ohms in stock

Arn

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arte444
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06-23-2013 05:30 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

hooked up both pots in series. adjusted both pots both directs and no change just pegged. with the car running. with the key on motor off, can turn the pots and the needle moves. can one of you just recommend to me wha pot to buy?

------------------
-Kyle
Email: kakagiraffe@gmail.com
1988 Notchback 4900SC 5spd Isuzu, Spec Stage 4
True Dual Exhaust, Delta Cam
1992 Honda Civic EX
2006 Pontiac G6 Ecotec

[This message has been edited by arte444 (edited 06-23-2013).]

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phonedawgz
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06-23-2013 06:23 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post

You should figure out what you have first. Take the ohm meter and try it across different pins on one of the resistors. Once you have it figured out then figure out how to get the desired 240K ohms. Hopefully you will also have figured out how to adjust it. Remember with the ohm meter when you are playing with the resistors that a lower resistance is going to give you a higher RPM figure.

Maybe your pots are broke? Maybe they got over extended and the wiper doesn't move at all? idk but I think you should be able to find somehow to get an adjustable resistance out of them and then shoot for the target of 240K ohm.

If you are getting a total of 240 k ohm on the resistors but the tach is way off then you need to look at what is wrong with the way you wired to the tach.

---

You can buy a fixed 240k ohm resistor for cheap ($1.00). The problem however is figuring if the resistors are the problem or the way you are hooking it up is the problem.

---

Here you can purchase a 500K pot for $3.25. Tell the guy to throw the other 4 away and put yours in an envelope and mail it to you USPS First Class mail. Then using just this pot cut pin 3 shorter and preadjust it so you have the 240K ohms between pins 1 & 2 and solder it in.

http://i.ebayimg.com/t/5x-3...Q8gD4ZmLw~~60_57.JPG

http://www.ebay.com/itm/5x-...&hash=item3a81c9e538

[This message has been edited by phonedawgz (edited 06-23-2013).]

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trotterlg
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06-23-2013 06:49 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post

Are you sure you cut the trace?

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arte444
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06-23-2013 08:40 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

http://imageshack.us/a/img407/2443/z5d2.jpg

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arte444
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06-25-2013 01:56 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

I ordered the pots you recommended above. Thank you. I'll let you know how it works when they arrive.

I did find out one of the pots I had was broken.

Right now I have them disconnected and I noticed my oil pressure gauge is not functioning anymore =( Maybe it will come back when the correct pots are installed.

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phonedawgz
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06-25-2013 03:34 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post

Cutting the trace or swapping the resistor on the tach won't have an effect on the oil pressure gauge.

Sorry.

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arte444
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06-25-2013 07:19 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by phonedawgz:

Cutting the trace or swapping the resistor on the tach won't have an effect on the oil pressure gauge.

Sorry.


Damn. That means something is broken =(

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arte444
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07-16-2013 10:15 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

Still havent figured out whats wrong. I bought some new pots from ebay and set to 210k with an expensive digital ohm meter at work. hooked them up and it ran for 2 seconds at the correct rpm then pegged the tach once again. I'm pretty sure i did a good job cutting the trace but I guess i will have to take it apart again. Oil gauge is also still not working.

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NJD85GT
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07-16-2013 10:21 PM Click Here to See the Profile for NJD85GTSend a Private Message to NJD85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

When I did my tach mod I didn't cut the trace, I added a 1 M Ohm pot resistor in parallel.

------------------
1985 GT | 4.9 Allante | M17/MY8 Hybrid 4-Spd Muncie | '88 GT Cradle Swap

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trotterlg
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07-16-2013 10:26 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post

I can say that the fix shown that leaves a pin floating (cut trace) on an IC is sort of odd. This is not normally done, a floating pin usually goes high or low on it's own, so is usually tied to something. Not saying it is wrong, but are you really sure the fix you are doing really works in the real world? Larry

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olejoedad
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07-17-2013 08:28 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post

Forum member JGunnset does a great job with tachometer calibrations.....

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Arns85GT
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07-17-2013 08:59 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

Since I've been playing with my swap, I've got my idle down to 600 and with the capacitor I changed, I am now within 100 of dead on. Not perfect, but it works well enough for me.

Arn

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arte444
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07-17-2013 03:33 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

Does this look correct? Also is it possible to hook up backwards?


http://imageshack.us/a/img407/2443/z5d2.jpg

[This message has been edited by arte444 (edited 07-17-2013).]

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Arns85GT
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07-17-2013 06:03 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

That's how I did my spare tach and I couldn't get it to read correctly. I ended up with the capacitor swap instead.

Arn

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Fieroseverywhere
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07-17-2013 11:26 PM Click Here to See the Profile for FieroseverywhereClick Here to Email FieroseverywhereSend a Private Message to FieroseverywhereEdit/Delete MessageReply w/QuoteDirect Link to This Post

I used a V6 tach and 200k pot, cut the trace as shown in your pick, soldered in with lead wires (to hang below dash for adjustment), and dialed it in. I have never had a problem or had to re-adjust. I've checked with the scanner a few times and its always dead on.

http://www.fieros.de/en/articles/tach.html

[This message has been edited by Fieroseverywhere (edited 07-17-2013).]

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arte444
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07-18-2013 08:10 AM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

Mine started as a 4cyl. Is this the problem? I still need the same resistance as a v6 tach?

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Mickey_Moose
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07-19-2013 01:16 PM Click Here to See the Profile for Mickey_MooseClick Here to visit Mickey_Moose's HomePageClick Here to Email Mickey_MooseSend a Private Message to Mickey_MooseEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by arte444:

It has 3 pin outs and im using #1 & #2. It also seems to register at 200k best I can tell with my ohm meter.



Best practice is to connect pins 2 and 3 together and make your wire connections to pins 1 and 2/3. Check with an ohm meter to make sure it 'adjusts'.


 
quote
Originally posted by trotterlg:

I can say that the fix shown that leaves a pin floating (cut trace) on an IC is sort of odd. This is not normally done, a floating pin usually goes high or low on it's own, so is usually tied to something. Not saying it is wrong, but are you really sure the fix you are doing really works in the real world? Larry


It's not an IC - it's a resistor network. You are replacing the laser cut 'calibrated' resistor on the 'chip' with an adjustable one.


 
quote
Originally posted by arte444:

Mine started as a 4cyl. Is this the problem? I still need the same resistance as a v6 tach?


Yes, that is the problem - you should be in the following ranges:

840K ohms is for the 4 cylinders with DIS
420K ohms is for the 4 cylinders w/o DIS

Edit: you can still use the ones you bought, just pick up a ~680k-720k ohm resistor (or a ~240k-300k ohm) one and add it is series. Radio shack should have these or try Digikey - does NOT have to be those values exactly, but around there - basically your 200k pot + xxxk ohms to equal the 840k/420k (make sure you give yourself some padding for adjustment.

Here is a link to what I would use for a pot: http://www.digikey.ca/produ...96W-204LF-ND/1088052

Use this one to select your resistor value (select resistance and check the in stock box and pick one from the search results - 1/4 watt one is big enough): http://www.digikey.ca/produ...ors/66690?k=resistor

If you get no results in the search, pick a different value.

[This message has been edited by Mickey_Moose (edited 07-19-2013).]

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arte444
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07-19-2013 01:36 PM Click Here to See the Profile for arte444Click Here to Email arte444Send a Private Message to arte444Edit/Delete MessageReply w/QuoteDirect Link to This Post

Mine was an 88 4cyl so I think it was DIS. I should be shooting for 840k to make my v8 register correctly. I'll give that a try. Thank you very much!

I'll let you know how it goes.

[This message has been edited by arte444 (edited 07-19-2013).]

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