I am undergoing a transplant project involving instrument clusters. I have a cluster that came out of a 6 cylinder vehicle and I am attempting to install in into one equipped with a 4 cylinder engine. I understand that there is a resistor of some sort that must be changed in order for the tach to read correctly. Can anyone help me with part number and/or sources for the resistor that I need to replace and maybe even some help identifying it? Any help whatsoever would be greatly appreciated.

Thanks in advance!

John P.

I did it on my coupe and you can either swap a resistor or a capacitor or both, (it's an RC circuit that determines deflection of the needle.)

My car is an auto so it's not that critical, I just swapped the cap. I wish I could tell you the value, but I don't remember. It's the cap at the very top of the cicuit board. I bet a search through the archives would turn up the value.

If you do nothing the rev limiter is still controlled by the ECM. There is no danger to the engine by having a tach that's not calibrated.

When I installed GT guages into my old 88 coupe I wanted to use the V6 tach with my 4cyl. All I did was remove your tach from the cluster and look at the back. There will be a small white plate with maybe yellow or a green dot on it. Its held in place by 2 nuts. If you look at the the other tach you will see the same small plate except it will have a different color dot. Just swap them. Thats all I did to make a v6 tach work in a duke. I wish I could show you a pic but I have nothing. If you dont understand take a pic of the back of a tach removed from the cluster and I will circle it.

Steven

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'02 Subaru WRX 14.61@91.87mph bone stock
'87 Fiero GT 4.9/4T60e w/3.33 final drive, ZEX nitrous 65hp shot, 88 cradle w/ 325# coil overs, Poly everything, Upgraded sway bars, KYB's, 16X7 M11's, 11.25 "Zettner" front brakes, Complete MSD ignition w/ 6AL box, Custom 2.5" Flowmaster exhaust, Grand Sport Corvette paint, Carbon fiber interior trim, '98 T/A CD w/ ETR, Reverse Indiglo guages, Pillar mounted AutoMeter O2, Hella H4 conversion.
Follow its built up here:
https://www.fiero.nl/forum/Forum1/HTML/027460.html
Sadly... SOLD.

That is interesting... I hadn't heard that one before. I do have a link to this page which goes into detail on it Http://www.fieros.de/en/main.html
After you get there click on English
Then reverse engineering the Fiero tach
I need to do the same thing my engine puts out a four cylinder tach signal.

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LS1 v8 T-Top 87 GT

http://www.acxunlimited.com/ls1swap.htm

I just swapped the circuit boards. Took my old circuit board and installed it on the new tach. The gauge "mechanicals" are the same. The electronics are the only difference. Worked perfectly.
(This may be what Steven was talking about, too. I don't remember mine being white, though.)

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Raydar
88 3.4 coupe.

Coming soon...
88 Formula, presently under the knife.

The circuit board swap is the easier way to go. I had forgotten about that one. If you have both sets of gauges in front of you it should be obvious which part to swap. Good luck.

Further to LS1swap's entry, and using the link he provides:

I was able to do the conversion by scrapping off the connection on the circuit board at the point illustrated on the website. To obtain the proper resistance I added two different resistor values. These I got at Radio Shack and even though they come in packs of 5 -- so I had to buy two different packs -- the price was less than $5.00.

To get the best approximation, I used a meter to test each resistor and chose the closest values. I got close enough, not perfectly. I suspect my Tach now reads almost 100RPM more than the previous one. Then again, who knows...maybe this is a more accurate report of true RPMs.

If I find some other details, I'll post them later today.

You can also put a fixed resistor in of slighty lower than 'recommended' value, then put a small variable one in series with it. Hook up a known good 'test tach' to the engine (my timing light has one built in for example) and run it up to mid scale (~3000 rpm) and hold it. Now just tweak the variable until the two tachs match!

Use a variable that's designed to me mounted on a PC board - you use a tiny screwdriver to adjust them, and they're pretty stiff so it shouldn't slip.

Try to do it all at normal cabin temperature (like, not when it's -20!) for best accuracy.

You dont have to solder anything... please if someone will post a pic of the back of a stock fiero tach I will circle what you have to swap. Its so simple, takes 15 seconds to do. No cutting, splicing nothing, simple remove/replace. I dont have my old computer or I would post a pic.

Unfortunately, I do not have a 4 cyl tach board to swap. Does anyone have one that they could sell for cheap to bring my project along?

Thanks!

John P.

You don't need to swap the tach boards, as far as I know. They all seem to be the same, with minor value differences. My old and new boards were certainly mirror images of each other (86 2.5l/5spd ). The mods are not rocket science. Just study the suggestions above and/or the ones at http://www.fieros.de/en/main.html -- Menu "Articles", topic: Tachometer reverse engineered. Mine is a distributor system, I just added up resistances up to 420k (soldered 3 resistors, 2 of the same value and the balance with another, all in series).
Example: --100k--100k--220k-- . These are Radio Shack 5% tolerance and 1/2 watt. I also scraped off the circuit board at the point illustrated in the website. I used a small fine screwdriver to do this.

Swapping may not be a good idea: it is likely that the old dial will look odd in the new panel. I believe that in many cases the way the 4cyl. panels are illuminated is different from the way the 6cyl. are. That was my case. The 6cyl. dials are translucent and lighted from behind. My old one (4cyl.) got light reflected around the edges. If your new board dials have a rubber edge on top and your old ones don't, you will know.

I've heard that some people have mixed dials...with mixed results.

HOWEVER...the dial redlines are different so you have to keep this in mind. I have already found myself pushing revs past safety a couple of times...but just briefly .

(edited to add comment about illumination and add details that I just remembered)

[This message has been edited by Jdlog (edited 12-03-2003).]

[This message has been edited by Jdlog (edited 12-03-2003).]

Go to this link which is a good overview of what you need to do to make any conversion you want to the tach. You'll have to do a little reading, but I do mention what value of capacitor you need when it's reading signals from a 4-cylinder car...
https://www.fiero.nl/forum/Forum2/HTML/037230.html

I give up. You dont have to solder anything... I keep saying it but you all arent getting it. All you have to swap from one tach to the other is a small 3/4 x 1/2 white plate bolted (w/2 bolts) to the back of the tach (in the center). Thats it. Really, its that simple. Dont ask me how or why but it works.

I found a mistake in my previous posting and corrected the resistor values...sorry. The Radio Shack website has them as items 271-1132 and 271-1131 at: http://www.radioshack.com but I got them at a store.

I wish I could find some pictures so that BV MotorSports may show us the location of the simpler procedure. This would be ideal!