93 z28
Ok, I'll take my pee pee smack and be nice. Welcome to the forum, tell us about your ride, post some pics and let us know the plans. 93 is kinda the step child of LT 4Th gens. Nothing at all wrong with em they're just a tad different but I always loved the yellow buttons for door switches!!
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Teching In
Joined: Sep 2019
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Ok, I'll take my pee pee smack and be nice. Welcome to the forum, tell us about your ride, post some pics and let us know the plans. 93 is kinda the step child of LT 4Th gens. Nothing at all wrong with em they're just a tad different but I always loved the yellow buttons for door switches!!
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Teching In
Joined: Sep 2019
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🖕🖕🖕😁 now i must apologize to anyone else for offensive or rude behavior. 
Launching!
Joined: Jul 2019
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No need to be such a dick.. This is my first Z28. My first car was a 94 with the 3.5 5 spd and with it i fell in love with these cars. I ask about the 93 cuz they have the unique tach feed and my tach doesnt work. It sits around 800 rpm until u rev it, it will go to around 1 and a half g and then bottom out. I was gonna ask if anyone has had this issue and what they did to fix it so that i can get some idea of where to start. I didnt use facebook for this type of problem, nor any other social media site. Im just a poor ole country boy from scott county tennessee. I live around the smoky mountains. I have always had to tear into vehicles on my own and learn it myself. Ive worked o. Numerous vehicles and engines but i have also learned that these 4th gens are a lil bit of a pain but shes so worth it. But to start i wanted to know bout the tach. Thnks in advance for any help or input that u can give, i truly appreciate it. Amd also ask that anyone that wants to criticize or make fun of a good ole boy, could you politely go eat a fat one.. thanks
Thread Starter
Teching In
Joined: Sep 2019
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Ive tried, it give a list of all possible problems, i asked on here to see if there are or have been others with same or similar issue.
No need to be such a dick.. This is my first Z28. My first car was a 94 with the 3.5 5 spd and with it i fell in love with these cars. I ask about the 93 cuz they have the unique tach feed and my tach doesnt work. It sits around 800 rpm until u rev it, it will go to around 1 and a half g and then bottom out. I was gonna ask if anyone has had this issue and what they did to fix it so that i can get some idea of where to start. I didnt use facebook for this type of problem, nor any other social media site. Im just a poor ole country boy from scott county tennessee. I live around the smoky mountains. I have always had to tear into vehicles on my own and learn it myself. Ive worked o. Numerous vehicles and engines but i have also learned that these 4th gens are a lil bit of a pain but shes so worth it. But to start i wanted to know bout the tach. Thnks in advance for any help or input that u can give, i truly appreciate it. Amd also ask that anyone that wants to criticize or make fun of a good ole boy, could you politely go eat a fat one.. thanks
The tach signal comes from the PCM, you may be able to find a wiring diagram on Shoebox site which you can also find if you Google 4th Gen f body wiring diagrams. Once you find the wire start to check it for good connections, chaffing, make sure that a mouse hasn't chewed on the wiring somewhere etc. I "think" your signal will come from the coil to the PCM IIRC so check wiring there as well. Otherwise you may just simply have an issue with the cluster itself. The factory tach has proven to not be accurate anyway and most end up installing a nice aftermarket tach.
The tach signal comes from the PCM, you may be able to find a wiring diagram on Shoebox site which you can also find if you Google 4th Gen f body wiring diagrams. Once you find the wire start to check it for good connections, chaffing, make sure that a mouse hasn't chewed on the wiring somewhere etc. I "think" your signal will come from the coil to the PCM IIRC so check wiring there as well. Otherwise you may just simply have an issue with the cluster itself. The factory tach has proven to not be accurate anyway and most end up installing a nice aftermarket tach.
I've got the same issue the OP has but for a different reason. I was removing wires no longer used in my harness and may have cut the single wire that leads to the PCM way up in the harness and then rewrapped the harness. Grrrr...but I can't say for 100% certainty it was the tach signal wire. I'm old and memory wanes me. Looking at the old XFI install there's mention but doesn't give me the pin out so I how I did it and had it running is beyond me. But if I find where the single wire runs to the PCM I'll be sure to post it.
OP after a little digging on the PCM connector pin A-12 is the ignition control and the single white wire. Granted it doesn't say "Tach Signal but if you look at Shoebox schematic for instance where it shows the opti and all the wires associated with the ignition control module harness. That white wire leads to there then onto the tach filter then onto the back of the dash to the tach which is a single white wire.
Last edited by SRZ; Nov 2, 2019 at 06:34 PM.
Thread Starter
Teching In
Joined: Sep 2019
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I was told the same thing in that the signal comes from the PCM on a 93 but I've yet to confirm it and I've got the big red book. I've looked and looked but I will say YEARS ago when setting up my XFI I believe I had to splice into the factory pcm to get the tach signal. Without it the car wouldn't fire as the XFI didn't see a tach signal.
I've got the same issue the OP has but for a different reason. I was removing wires no longer used in my harness and may have cut the single wire that leads to the PCM way up in the harness and then rewrapped the harness. Grrrr...but I can't say for 100% certainty it was the tach signal wire. I'm old and memory wanes me. Looking at the old XFI install there's mention but doesn't give me the pin out so I how I did it and had it running is beyond me. But if I find where the single wire runs to the PCM I'll be sure to post it.
OP after a little digging on the PCM connector pin A-12 is the ignition control and the single white wire. Granted it doesn't say "Tach Signal but if you look at Shoebox schematic for instance where it shows the opti and all the wires associated with the ignition control module harness. That white wire leads to there then onto the tach filter then onto the back of the dash to the tach which is a single white wire.
I've got the same issue the OP has but for a different reason. I was removing wires no longer used in my harness and may have cut the single wire that leads to the PCM way up in the harness and then rewrapped the harness. Grrrr...but I can't say for 100% certainty it was the tach signal wire. I'm old and memory wanes me. Looking at the old XFI install there's mention but doesn't give me the pin out so I how I did it and had it running is beyond me. But if I find where the single wire runs to the PCM I'll be sure to post it.
OP after a little digging on the PCM connector pin A-12 is the ignition control and the single white wire. Granted it doesn't say "Tach Signal but if you look at Shoebox schematic for instance where it shows the opti and all the wires associated with the ignition control module harness. That white wire leads to there then onto the tach filter then onto the back of the dash to the tach which is a single white wire.
Thread Starter
Teching In
Joined: Sep 2019
Posts: 10
Likes: 0
The tach signal comes from the PCM, you may be able to find a wiring diagram on Shoebox site which you can also find if you Google 4th Gen f body wiring diagrams. Once you find the wire start to check it for good connections, chaffing, make sure that a mouse hasn't chewed on the wiring somewhere etc. I "think" your signal will come from the coil to the PCM IIRC so check wiring there as well. Otherwise you may just simply have an issue with the cluster itself. The factory tach has proven to not be accurate anyway and most end up installing a nice aftermarket tach.
Your welcome. Post an update if you get it sorted out. I'm in the process of trying to fix it myself as it's annoying. My challenge is a lil different though as I'm running coil over plug and not a single coil with ICM. Hoping in theory I can tap into the #1 coil wire harness plug and go from there. Just have to figure out which wire to tap as I've seen little wire schematics for them.