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91camaro_rs Member
Joined: 03 Dec 2008 Posts: 1712 Location: Fox Island, Wa
1991 Chevrolet Camaro RS
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Posted: Thu Nov 04, 2010 11:57 am Post subject: how do tachs work |
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ok so im wondering how my tach works for my car, i know that it has to do with resistance and thats what makes the tach move up and down, but where is the tach getting the signal from? and what wires and connectors are involved, when i replaced my ecm it worked great for 3 weeks and started to go crazy, there has to be a wire that came loose or something _________________
'91 Camaro RS 5.7 TPI- 700r4- 3.27 posi- headers- chambered exhaust- |
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Twilightoptics Hardcore (12sec Club)
Joined: 13 Jan 2004 Posts: 9191 Location: Auburn , WA
1987 Chevrolet Camaro IROC-Z
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Posted: Thu Nov 04, 2010 2:53 pm Post subject: |
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Ign Power
Ground
Coil Negative
Those are the 3 wires. In the case of your Camaro, power an ground are intigrated into the dash circuit overlay.
So it's just a single wire going to the coil -. _________________ A redline a day keeps the carbon away! |
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91RSVert Member
Joined: 16 May 2007 Posts: 2736 Location: AR
1991 Chevrolet Camaro RS
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Posted: Fri Nov 05, 2010 4:09 am Post subject: |
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IIRC, its the white one off the coil too.
The little circuit boards inside the cluster are known for going bad. _________________ 2008 GMC Z71
1991 Camaro RS Vert
1972 Jimmy 4x4
20ft Longhorn Car Hauler
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chevymad Master B
Joined: 11 Jan 2004 Posts: 5474
1987 Pontiac Formula
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Posted: Fri Nov 05, 2010 1:43 pm Post subject: |
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A jumpy tach is also a sign of jumping spark in the ignition secondary. |
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91camaro_rs Member
Joined: 03 Dec 2008 Posts: 1712 Location: Fox Island, Wa
1991 Chevrolet Camaro RS
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Posted: Fri Nov 05, 2010 2:05 pm Post subject: |
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Where would I look to make sure that's not the case _________________
'91 Camaro RS 5.7 TPI- 700r4- 3.27 posi- headers- chambered exhaust- |
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chevymad Master B
Joined: 11 Jan 2004 Posts: 5474
1987 Pontiac Formula
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Posted: Fri Nov 05, 2010 2:19 pm Post subject: |
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Ignition secondary is any of the high voltage ignition components. Coil, distributor cap, rotor, wires, or spark plugs. Do you have a miss? With the engine running do you hear any clicks or snaps that might be spark jumping? Make sure all the wires are plugged in good and tight. Look for gray marks on the wires where they touch or touch something else. That is a sign of spark jumping out of the wire. |
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simpson6716 New Member
Joined: 08 Sep 2010 Posts: 12 Location: Adair Village,OR
1985 Chevrolet Camaro Z/28
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Posted: Fri Nov 05, 2010 8:09 pm Post subject: |
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I have a question about tachs. What would make my tach stay at 2500 rpm and then sometimes work? Even with the car off it stays at 2500. |
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chevymad Master B
Joined: 11 Jan 2004 Posts: 5474
1987 Pontiac Formula
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Posted: Fri Nov 05, 2010 8:18 pm Post subject: |
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That sounds like it's probably the tach itself. Like possibly the movement is sticky. |
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simpson6716 New Member
Joined: 08 Sep 2010 Posts: 12 Location: Adair Village,OR
1985 Chevrolet Camaro Z/28
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Posted: Fri Nov 05, 2010 8:33 pm Post subject: |
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chevymad wrote: | That sounds like it's probably the tach itself. Like possibly the movement is sticky. |
It does work sometimes and it moves fine when it does work even below 2500. Is there something between the distributor and the tack that might make it not read all the time? |
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chevymad Master B
Joined: 11 Jan 2004 Posts: 5474
1987 Pontiac Formula
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Posted: Fri Nov 05, 2010 8:46 pm Post subject: |
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As stated earlier, there's only 3 wires making a tach work. One of them comes directly from the coil. The others are power and ground. Break any of them and the tach won't work. But I still think its actually in your gauge.
You might try pulling your instrument cluster and making sure that the plug in is clean and making good connection. |
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91camaro_rs Member
Joined: 03 Dec 2008 Posts: 1712 Location: Fox Island, Wa
1991 Chevrolet Camaro RS
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Posted: Sat Nov 06, 2010 12:33 am Post subject: |
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Try doing the resistor fix to the tach chip that should fix it unless you already did it, there is a thread on tgo about it
And now that I think about it one of my spark plug wires got burned by the header, maybe its arking somewhere, I think I'm gonna get all new plug wires with for the new motor
And today my tach was actually working below 2k _________________
'91 Camaro RS 5.7 TPI- 700r4- 3.27 posi- headers- chambered exhaust- |
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aaron_sK Member
Joined: 23 Jan 2006 Posts: 8834 Location: Back in beautiful Tacompton
1987 Chevrolet Camaro IROC-Z
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Posted: Sat Nov 06, 2010 8:34 am Post subject: |
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91camaro_rs wrote: | Try doing the resistor fix to the tach chip that should fix it unless you already did it, there is a thread on tgo about it |
That "fix" is specific to the later 90-92 cars. He has an '85. There is a capacitor that is known to go bad in the earlier ones, more info on that can be found here:
http://www.thirdgen.org/techboard/electronics/114057-tach-fixed.html
If you're going to buy new plug wires, get some wire looms and strap stuff up right. Burnt wires ain't the wire's fault. Misfiring more as revs go up does sound like a burnt wire though. |
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chevymad Master B
Joined: 11 Jan 2004 Posts: 5474
1987 Pontiac Formula
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Posted: Sat Nov 06, 2010 12:07 pm Post subject: |
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I've been reading more and more about capacitor failures in all kinds of electronic equipment. This last year I had to go through my Klipsch subwoofer and replace all the caps. Replaced them with military grade components.
Really sounding like planned obsolescence here. |
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BluFbdy Member
Joined: 16 Jul 2010 Posts: 915 Location: Port Orchard WA
1989 Chevrolet Camaro RS
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Posted: Wed Nov 17, 2010 2:03 am Post subject: |
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simpson6716 wrote: | chevymad wrote: | That sounds like it's probably the tach itself. Like possibly the movement is sticky. |
It does work sometimes and it moves fine when it does work even below 2500. Is there something between the distributor and the tack that might make it not read all the time? |
have you ever pulled your cluster? mine has been known to bounce around and dance, never go below 2500 etc but thats from the connector not sitting in the PCB correctly, make sure all the connections are tight and go from there, if it doesnt work id go JY'in it _________________ If you expect a kick to the balls and get a slap to the face its still a victory
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91camaro_rs Member
Joined: 03 Dec 2008 Posts: 1712 Location: Fox Island, Wa
1991 Chevrolet Camaro RS
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Posted: Wed Nov 17, 2010 8:07 am Post subject: |
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mine ended up being the white wire that goes into the coil, it was loose... _________________
'91 Camaro RS 5.7 TPI- 700r4- 3.27 posi- headers- chambered exhaust- |
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