This is the second one that's gone **** up on me within two years and don't know why. They both started out the same. Start reading close to double what the actual RPMs are, then just tach out no matter if you're idling or what. I noticed this when my 1-2 and 2-3 shift showed 7000 RPMs at WOT!

Then noticed yesterday that I was running 3,000 RPMs at 70 MPH with 2.77 gears (88 350 TPI).

So now I have two, useless tachs and would like to see if they're fixable before forking out the change for a new one ... again ...

 

Check here and give it a try, you might get lucky.

https://www.thirdgen.org/techbb2/sho...hreadid=114057

 

I am going to try morleys fix on my tach, I will let you all know how it goes. I was going to do it this weekend but the electronics store was closed But I do have a spare circuit board from another tach to work on so I wont screw mine up worse will get the parts tomorrow.

 

Check where?

Are you talking about the post where you used a 6 cyl S-10 tach and swapped the capacitor? If so, I don't think that'll help. The one you are talking about (at the 3250 RPM spot) is marked .068 uf and it measures .061uf with my Fluke so I'm thinking it's not bad ... if I were to replace it with the .0033uf one, who knows! but I'm thinking it may be one of them stupid chips on there and if I only knew what they were, maybe I could try those ....

 

Sorry, forgot the link. .0068Uf is what was in the 6 cyl tach I have the 8 had a .0036 in it, did someone sell you a 6 cyl one by mistake?

 

I don't think so, are there V6 Camaros that have the IROC-Z Tach?!?

Anyway, I'm actually troubleshooting the original tach out of it. That's the one that has the .0068 uf cap in it. yes, i am confused. If anyone is buying those .0033 uf caps in bulk, I'll pay for a couple!

 

Yes, the V6 had the same tach as the V8's except for one capacitor on the PC board

 

Interesting, both of my tachs, the original included, have a .0068uF cap on them. I'll try the .0033 cap on the one the somewhat works ... the other one I have pegs the needle (original). I'm thinking it's the chip on it. Never seen one of those before.

It's got these numbers on it:

1597423H
CTS8804

Somebody designed this POS so there has to be a schematic for it somewhere ...

 

I'll look up those numbers in my Mouser catalog and see if they come up.

Nope, those numbers don't match anything in the catalog.

I did find a couple places on the net that do Tach repairs... $95-$125 to do it though.

 

Morley, I just want to clarify this before I Solder in the wrong piece. I have board from a V6 tach, the cap is labled .068 150v not .0068 should I be looking for a .033 or a .0033 cap to correct it? Should it be a 100v or a 150v? JUst wanna get this right the first time

 

I used what was posted to me in the other Tach thread .0033Uf 125V (I used 100V because no one carried a 125V) This did correct my problem of reading 500 RPM too high at idle and more at higher RPM's.

 

I just converted my v6 tach to a work with a v8 by changing the .0068uf capacitor found under 5750 (above the oil gauge) to a .0033uf (332M) not the .068uf capacitor found under 3250. My gauge works Great with the v8 now.

 

Wow, woke this post up from the dead didn't we? I have a new tach since then, but I'll keep a mind on the tips if I have to worry about it again.

 

Hey group, I recently bought a 91 RS with the 305 , and when I picked it up the tach read about 2x the actual RPM. I went through the check sequence outlined in the factory shop manual and everything checked OK, so I got another dash cluster and swapped the tachs.

BUT when I re-installed the cluster, the second tach reads just as high as the old one. It shows 1500+ RPM at idle, and shoots up fast - at least 2x the actual RPM - when I accelerate. No improvement!

QUESTION:

Is the capacitor replacement outlined in this discussion ONLY used to adapt a V6 tach for a V8, or is the capacitor a known failure item for this tach? If the capacitor has a habit of failing, it's possible I got two bad tachs. If so, it wouldn't be hard to replace the cap and get this tach reading correctly.

 

I've had the same problem with my '92 RS. It reads at least 2,000 more than I'm actually doing. I got a new gauge cluster, swapped tachs, same outcome. I went ahead and bought an Autometer tach and I'll have that installed soon. I doubt there is any real fix when these stock tachs go whacky.

 

Replacing the capacitor should work. A good number of people have gotten their "wacky" tachs to read correctly, in their 82-89 Camaro gauges. The interesting part is that I have yet to see someone attempt to replace the capacitor on the 90-92 Camaro half-moon style gauges and have the tach read correctly. I wouldn't be surprised at all if both clusters you have are bad, this problem is really common in the 90-92 tachs. This same topic comes up at least once a month.

I also have the same problem, but I just broke down and got an Autometer tachometer as well, and have had it installed for almost a year now. It still bugs me having 2 tachs in the car.

 

That's encouraging! I don't have a lot to lose, as a cap is cheap and it won't take that much work to get at the board and try replacing it. The darn tach doesn't read right anyway.

I also agree with you - having another tach sitting right in front of one that SHOULD work would probably bother me a lot.

 

If the caps are electrolytic they will go bad over time and 20 years has passed for mine. Try replacing all of the caps. My problem is that the writing is worn off of my capacitors so I don't know what to replace mine with.

 

I have an 89 TPI V8 IROC and a spare taken from an 87. I can't swear they are original but both of them have the .0068 cap. I removed them both and they measured in spec. I tried the .0033 and it did not help. I also tried replacing the .068 with a .0033 and it went off the scale. Ok so there is probably alot of misinformation being spread by alot of well meaning people who think they know the fix because they read it somewhere or heard it somewhere but I have not found a single post anywhere of a person having a v8 tach and fixing it with a cap .. period. I think if this really worked there would be more people chiming in about their success story. There is a post of someone saying it is a resistor on a chip and without a schematic we won't know but could forma an RC network which is why some people have influenced a change by compensating for the increased resistance by change the capictance but you cannot reach a calibration this way. BTW./ On my spare tach someone had soldered a reisistor across one of the components that led back in parallel with the reistor chip. It had no effect because it was 10meg across a 250k resistance but My tach was reading about 620k across the same point. Now my tach is reading 2000rpm and the spare is reading 1500 rpm at idle so this maybe the point to experiment with but I didn't have a wirewound pot more than 10k.