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I hope this is the right forum for this question?? I just installed a z-28 6,000 redline OEM tach in my '67 (non-tach model). I just started the car for the 1st time. 'Roughly' 900 rpms read 2300 at idle.

HELP!

Thanks guys!
 

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Is this with it connected to the the TACH output wire from the MSD box?
 

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yes - ground to chasis, signal to the box, and red to ignition - from the OEM Tach
 

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Tach is reading the multiple sparks, it senses the changes in voltage, highs & lows.
2300 / 3 = approx 900 rpm.

Might try a MSD tach filter with the filter hooked to the coil as per instructions rather than using the TACH spade on the MSD for the OE tach. TACH spade would work for an aftermarket tach.
 

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No filter installed. I didn't need on with my column mounted tach. Fortunately I have a Summit Racing 7 miles from my house. I will go grab one (if in stock) and report back.

As always --> Thanks Guys!
 

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I had the exact same situation.... plus ... as the engine RPMs increased, the tach needle increased disproportionately.... It was way outa wack... I installed the 8920 tach filter. Its better than it was... Close at idle but it is still off by about 500 RPMS at 70mph. VERY irratating situation. I hope you have better luck with it than I did....

K
 

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I had the exact same situation.... plus ... as the engine RPMs increased, the tach needle increased disproportionately.... It was way outa wack... I installed the 8920 tach filter. Its better than it was... Close at idle but it is still off by about 500 RPMS at 70mph. VERY irratating situation. I hope you have better luck with it than I did....

K
How did you attach the 8920? I ignored the instruction and hooked it up initially 'in-line' with the old tach wiring and the tach wouldn't even work - Ground to ground, ignition to ignition, trigger to trigger, violet unplugged. I haven't had time to try the instruction route.
 

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I had the same issue. I changed out the fuel gauge for the tach and it was way off. The guy that installed it finally adjusted something behind the gauge(think he said he had to break a solder) to make the adjustment and ever since i have been within ~100rpm of my digital tach readout on my shiftlight.
 

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I had the same issue. I changed out the fuel gauge for the tach and it was way off. The guy that installed it finally adjusted something behind the gauge(think he said he had to break a solder) to make the adjustment and ever since i have been within ~100rpm of my digital tach readout on my shiftlight.
Thanks for that! Any idea what he did?

I have been thinking about the possibility of swapping out the internals with my old column mounted tach, but looks a little daunting.
 

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OK..according to the URL that Steiner posted, GM TACHs have an inline filter that has to be bypassed.. Any idea where this filter would be physically located?

I have a TIC-TOC in my car and I am thinking of getting an MSD system. My TAC connection consists of a single wire (can't make out the exact color) that goes to the negative side of the coil. I assume I have to disconnected it from the negative of the coil (as per MSD's instruction), remove the inline filter and then use the TAC connection on the side of the MSD unit. (?)


Vic
 

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OK..according to the URL that Steiner posted, GM TACHs have an inline filter that has to be bypassed.. Any idea where this filter would be physically located?

I have a TIC-TOC in my car and I am thinking of getting an MSD system. My TAC connection consists of a single wire (can't make out the exact color) that goes to the negative side of the coil. I assume I have to disconnected it from the negative of the coil (as per MSD's instruction), remove the inline filter and then use the TAC connection on the side of the MSD unit. (?)


Vic
Well I have my 69 Tach out of the dash at the moment. I think it is the one or both of the green circuits shown here. They are attached to a white circuit board that connects to the three lugs on the rear of the tach. I don't know if 68 Tic-Toc-Tach has the same guts. I think the wire color is brown going to the coil.
 

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Brown wire to coil and Brown to circuit board connector for '68. It is a straight wire to/from fuse block. Power is Pink wire in connector.
 

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Brown wire to coil and Brown to circuit board connector for '68. It is a straight wire to/from fuse block. Power is Pink wire in connector.
Can you expand on that some? Are you speaking of the internal wires in the tach? Since I am replacing the fuel gauge, and had no tach, I have no 'stock' tach wires. I have to run a trigger wire on my own + ignition + ground from the back of the OEM tach I just installed.

FYI (to all) I tried hooking the tach up stock = trigger to (-) side of coil, ignition, and ground --> the tach did not work at all.
 

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CB is explaining external wiring hook-up.
I believe ground is through the tach body.
Pink wire from fuse panel for power, brown wire to coil neg terminal.

There is a tach sticky of how to check the tach in Electrical.
 

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Sorry, I was at Infineon Raceway for NASCAR...

Yes, I was talking about external wiring to back of tach. The two posts and nuts on the back of the tach that connect to the printed circuit are for signal and power. I only have pictures of the back of the '67 clusters. But it appears that a third post and nut are under the circuit board for grounding to the housing.?.?

That would make it (viewing from the rear) top = ground, left = signal, and right = power posts. Also, the tach and non-tach circuit boards for '67s are the same. So, the power should be in the correct place. You should only have to replace the correct Tan fuel wire with a tach signal wire (Brown is stock) in the cluster connector. The Tan wire will go to your new fuel gauge, anywayz...

'68s don't have that additional ground post and have a non-threaded post for the clock power... They also have different circuit boards for tach and non-tach.

As far as not working in the test set up, are you connecting according to the MSD instructions? Everett's suggestion (to coil w/ filter)? Using a filter at all?
 

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I had the same problem when I pulled my fuel gauge and put in a oem tach. Since I had a MSD distrubutor I called their tech line and talked to one of there techs. They were super nice and they sent me 3 tach filters because he said they were not sire which would work. It had instructions and i didnt pay for it. They even paid for shipping. My tach is now good.
 

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I had the same problem when I pulled my fuel gauge and put in a oem tach. Since I had a MSD distrubutor I called their tech line and talked to one of there techs. They were super nice and they sent me 3 tach filters because he said they were not sire which would work. It had instructions and i didnt pay for it. They even paid for shipping. My tach is now good.
I will give this a try. I do have the 8920, which did not work. The tach would not work at all the way I wired it. I admittedly am being a little lazy on this because I have my engine compartment exactly the way I want it (some Team Camaro members have seen it at Hot August Nights) and don't want to remove the box.

I have modified the printed circuit sheet in back of the gauges to prevent shorting and am hooking the tach wires up direct from the tach posts. Once again my '67 had NO factory tach.

I will call the MSD tech line today, but they are the ones who told me to get the 8920 :confused:

Thanks guys!
 

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MSD did not offer up any help & the 8920 does NOT work. 750 RPMs (actual) = 2350 on the oem tach.
 
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