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Quick thanks to 92blue and others who contributed.
My experience regarding tachometer reading high: I signed up as a member onto Gen 3 Camaro Forum on 5/25/2015 Memorial day evening. Read many posts for about 2 hours. Whew! A lot of work has been done by members. Thanks, I am already reaping the rewards of your efforts. Member 92Blue summed earlier efforts up nicely.
Tuesday 5/26, I removed the gage cluster from my 1991 Camaro Z28. I then located the circuit board controlling the Tachometer. The resistor readings taken were: R1 = 5.75K, R2 = 3.84k, R3 = 1.91K, R4 = 495K, R5 = 4.32K, R6 = 2.95K.
I went to Radio Shack and bought some 100K resistors (5 pack for a buck and a half).
Followed the instructions provided and by soldering 2 - 100k resistors in series, I changed the 495k R4 reading to exactly 196K. Just lucky to have hit the goal on the head. Tomorrow, pray for me as I attempt to properly reinstall all the dash and not have any parts left over. If all works as I am hoping, I will add pictures of the effort.
This is one great forum! Thanks to all who helped determine this fix.
I did the repair in my '84 Trans Am. I first attempted to use a 500K ohms potentiometer, but at the max setting it still wasn't right. So I added a 400K ohms (or around that number) resistor in series with the potentiometer so I could adjust to a higher number of ohms. I haven't measured after adjusting the tach, it's still not perfectly accurate especially at very low rpms, but at least it works now and seems to be in the right range. I soldered the pot and the resistor at the end of a couple wires soldered to the board so I can adjust the pot with everything in place.
So in my case I need over 500K ohms in place of the bad resistor of the chip.
Hey so I finally got around to doing this. I decided to go with pots (two actually, so if it gets worse over time I can just crank it up).
I was wondering just in general what my car should be idling at. It's the 5L v8 automatic. I don't have a timing gun handy so I'm just trying to ballpark it for now. It's been so long since it worked properly I honestly don't know the correct values.
Absolutely amazing the amount of information and knowledge contained in one thread. Hats off to all you guys. I took the time and read everything here then I made my decision "just do it". I made a resistor strand that measures 190k ohm added a 10k mini "pot" and mounted remotely (empty light socket). Perfect for fine tuning preset it to 196.5k and it landed bang on. So I became a member of thirdgen.org great place for info. Oh my respack from pin #4 to #10 measured 398k ohm tach was showing exactly double vs timing gun reading.
You got to love when people come together to get something done. I put 2 100k ohm 1/2v resistors in parallel tested out at 196.5k ohm. and its working awesome. Easy and cheap fix couple of hours worth of work but well worth it. I am super happy about getting this working. I want to Thank everyone here for all the work on this and the great pics and feedback.
Last edited by Itsdice4me; 09-16-2015 at 10:01 PM.
You got to love when people come together to get something done. I put 2 100k ohm 1/2v resistors in parallel tested out at 196.5k ohm. and its working awesome. Easy and cheap fix couple of hours worth of work but well worth it. I am super happy about getting this working. I want to Thank everyone here for all the work on this and the great pics and feedback.
I had a potentiometer sitting behind the cluster for years.
Yesterday, I swapped in two 100 kohm resistors while doing a speedometer repair. It's finally done. done. I am still thinking about swapping once more to hit 196 kohms. I just didn't have the optimal resistors lying around to put that one together.
Count me as yet another successful fix story! Thanks go to 92blue (and all whom have participated in this fix discussion)!
92 Camaro Heritage Edition with 305 (with automatic transmission)- has instrument cluster 25088982 (has sticker underneath where the cluster scrapes the steering column as you're re-installing it). (Has 110MPH speedo and 7000rpm tach) Has the usual dead speedometer and crazy tachometer so many have experienced....
I used WinALDL to compare and it's practically dead on! My tachometer was reading way off like others (like 5000RPM at idle and pegged above that). What I did:
1. I cut the legs on 4 and 10 and measured- If my meter was correct it was 1.540 megaohms (yes 1 1/2 megaohms).
2. Bought a pack of 271-1131 100K ohm resistors from Radio Shack. Measured until I found the sweet spot everyone mentions (196K). Soldered those two resistors in series as mentioned many times here but soldered on the back side of the board as some have mentioned- it makes it MUCH easier!
3. Reinstalled the cluster and tested. Worked! Yea! At least I can use my tach to figure out my approx. speed now!
Now if I can only manage to fix the speedo! Board almost looks like a NOS except for one spot where it looks burnt just like Elephantismo mentions in his post (URL below) of which I added my question/problem onto since my board is also a 3.9 ohm instead of the typical 30 ohm board. If you know about speedos, please help!
Radio Shack has two different 100 Kilo-Ohm resistors: 1/2 Watts and 1/4 Watts; which one should we use? Or does it not matter? It should, though, right?
From what I've read, it shouldn't matter as there won't be enough current draw across it to make any difference. As I said, I bought the RS 271-1131 (as that's what my small RS had in stock).
I combined info from this thread, with info about an earlier camaro, and made it work.
I used the 196K ohm from here(made a series of 100k, and 2 47K, making a close 194k) and info from the other tech.
Instead I scratched off the wires from the back of the board, and wired directly, ignoring the chip completely.
Last edited by mustangman65_79; 12-30-2015 at 10:21 PM.
Reason: wrong values
You can add me to the list of successful tach repairs using this method !!
Thanks to 92Blue for starting and sharing his knowledge on this.
I used a single 196K, on back side, works like it should. Idles at about 700.
You could do this without removing the entire gauge cluster. Just remove the clear lens then the secondary trim behind that would expose the circuit board. You can see all the screws. Mine was a bit dirt so wanted to clean everything ...
Too make everybody feel better all my gaugges are screwed up or not working. I have an 87 Iroc-Z. Love my car and decided I need to fix this issue. Anybody know any good Camaro techs in the San Fernando Valley or LA area...Help! Help! Mayday! Mayday!
Wzup James, its sounds real simple I hopefully assume? Just want the gauges working and put back in place. Gauges are coming off the round circles. Possibly put a LED light instead of the yellowish orange light color. Its all 100% stock by the way
Some folks have had good results replacing bulbs & going to LED, and some have said console lights can't be dimmed after going to LED. My experience was the latter, so I went back to the originals. You need to provide more detail about the problems, though. It might be just a fuse. As I remember, the console is on the no. 10 fuse on my '91. That's the first thing to check.
Third Gen 24/7 - pull the cluster out and make sure the 2 board contact are properly seated to go into the gauge harness plugs mounted in the back of the dash. When I put mine back in it was screwed up cause a corner of the thin circuit board folded as I was pushing it in. I puled it back out and used scotch tape to make sure it was flattened out ... no problem after that.
Inorder to dim LEDs you have to keep 1 of the old type bulbs in the circuit, that may work. Or there are special LED dimmers. But the above is what I had to do in my boat.
Hi, New here, I am from New Zealand and have a imported 89 RS Convertible, I have a problem with my tacho reading high but i am unsure if it is the same issue you guys are describing, mine even with ignition turned off sits just under the red line, when i start it it jumps up to mid redline and then to the max of the gauge when driving, From what i gather this fix if for if the needle is just out but 1000rpm or so, Is this correct? Im thinking i may need a whole replacement tacho unit ?
I tried this fix. My tach was reading high around 4000 or so at idle. I measured all the res chip values everything was good except R4 was at 860k. I clipped the pins 4&10 and soldered 196k res. Tried it and I got no movement when revving the engine. I then resoldered the res this time from under side and tried again, got same. I was worried my tach was dead so I removed the 196k res and soldered the pins back to its original and plugged it back in and now it works but reads 1000 rpms low now.
I finally gave up #$%in with it.
I'm keeping it oem. I bought a refurbished calibrated Tach from Hawks,
that's my fix!
Nah, it was just the tach and board at $134. I could spend a day trying the junk yards but I have a feeling I would end up with another tach resistor fix nightmare. For mental sake, I just have to know if what I have been feeling is really 5K at WOT.
I have an '88 v6 and mine was reading 2x what it should, registered about 850k ohms, I put a 500k pot in mine but it needs some fine tuning. i've got it up to about 250k ohms but it still seems to be low. wish there was more info about this for those of us with v6's.
I have a 1990 5.0 RS . My tach was also reading very high. I removed the tach board and clipped 4 and 10 pin and soldered two 100 ohm resisters in series. Now when I crank the car the tach hand rises maybe a 1/2 inch and go`s no high. Does anyone have a suggestion to my problem. Not sure of the wattage of my resisters. Would it mater?
I have a 1990 5.0 RS . My tach was also reading very high. I removed the tach board and clipped 4 and 10 pin and soldered two 100 ohm resisters in series. Now when I crank the car the tach hand rises maybe a 1/2 inch and go`s no high. Does anyone have a suggestion to my problem. Not sure of the wattage of my resisters. Would it mater?
Do you really mean 100 ohm?
You need 100K ohm resistors, and no, I don't believe the wattage matters.
Thanks KCG we had some at work and it fixed my problem. Thank you and everyone who has posted in the forum. I would have never known what to do to fix my tach. Now to to start on my new problem. While I had the cluster out I put blue LED lights in my cluster and replaced my light switch. Now the buzzer that alerts you that your headlights are on buzzes while the engine is running even with the headlights off.
So I took my cluster out to fix my tach issue as well as my speedo issue (following another post for the speedo), put it all back in, turn the key and nothing. The battery doesn't even click on. No clue what I could have touched that would make it not want to even get power. Any suggestions??
05-16-2015, 11:06 PM
Thanks go to 92blue (and all whom have participated in this fix discussion)!
Board almost looks like a NOS except for one spot where it looks burnt just like Elephantismo mentions in his post (URL below) of which I added my question/problem onto since my board is also a 3.9 ohm instead of the typical 30 ohm board. If you know about speedos, please help! 
