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Discussion Starter · #1 ·
My tachometer is way off in my car it reads 1300 at idle and its really at 850 and at 3k its reading 5k so I thought it was my gauge so i installed an aftermarket unit and used the white and black wire which is the ground off of the ignition module and the aftermarket tach is reading the same as the factory tach. What would cause this? I have all new ignition system in the car other than the crank sensor. The distributor is new as well as the coil and ignition module. Any ideas would be great. Thanks
 

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It could be the electronics on the circuit board for the cluster. They do go south occasionally. It could be just a resistor failing, but I have not messed with them, so that is just a guess.
 

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Discussion Starter · #3 ·
I have to get a wiring diagram but I have it tapped in at the ignition module so I doubt its the board but depending on how its wired it could be. I am going to go try to tap it in at the computer next.
 

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You still have the stock instrument cluster? Also did you have any PCM programming done recently?
 

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Discussion Starter · #5 · (Edited)
Yes I have the stock cluster and yes a program was done with the lt1 edit.I just did a 383 with AI heads and cam and the first computer wouldnt take a program so I just installed a new one and got it dyno tuned.
 

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IIRC in tuning there isn't a way to check or change the tach resolution, it is what it is, I thought that the 96 SS tach in the cluster was a 4 cylinder resolution tach or something like that. Not sure why an aftermarket tapped at the coil would cause the same issue though.
 

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Yes I have the stock cluster and yes a program was done with the lt1 edit.I just did a 383 with AI heads and cam and the first computer wouldnt take a program so I just installed a new one and got it dyno tuned.
IF this is when the problem started it could be the settings in your tune. 96 uses a different tach signal then the OBD1 clusters / pcms. Make sure that setting is correct for obd2 and 96.
 

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Discussion Starter · #8 ·
I went back to my tunner and he said there is nothing in the LT1 edit to adjust that . But the funny thing is I tapped the wire at the ignition module the number 13 on the red connector and the number 5 on the black connector and all the readings are the same as the factory tach. The funny thing is if you go through the computer and compair readings the factory and my aftermarket tach I installed are off exectly 50% so if the scanner says 600rpms the tach says 1200 and if the scanner says 1500rpms the tach says 3000rpms. Does anyone know how to adjust this in the tune or anyother way. Its an 96 so it has the OBD II cluster and the new computer is OBD II as well.
 

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Sounds like you have a 96 cluster , If the LT1 edit used was 94-95 as a starting base tune, that is where the problem is at (I dont know lt1edit) . If he used a base program to work from (96) you should not have that problem, I would think. You may want to ask if he is using 96 programing as the base / starting tune. I know many tuners will use programs they already have stored and reflash the pcm with that tune and adjust accordingly. Just wondering if he flashed the starting tune with 94-95 first.
 
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