Lt4 tach swap from LT1
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 1,212
Likes: 0
From: OH
Lt4 tach swap from LT1
Okay so I got a nice looking LT4 cluster off Ebay, went to install today, everything worked good exact the tach, was about 1000rpm off. So idle was showing just about 0!
Reading about the swap didn't see anything might need to be changed, I'm assuming its a problem with the tach itself. Is this something that can be corrected or the unit is just junk?
Thanks
Reading about the swap didn't see anything might need to be changed, I'm assuming its a problem with the tach itself. Is this something that can be corrected or the unit is just junk?
Thanks
Pro
Joined: Jan 2005
Posts: 686
Likes: 62
From: San Jose Ca
I did the same swap and had no problems, at least none relating to the actual compatibility. The cluster that I recieved had a problem with the coolant temp gauge and there were some scratches on the lens. I basically only used the actual tach gauge and the main circuit board from the LT4 and everything else came from my stock cluster. In any event, there were no performance problems other than the tach reading approx 100rpm high, which is typical of factory tachs.
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
I'm not sure it this has anything to do with it, but here is a difference.
The '96 vehicles don't use a tach filter, the tach signal is conditioned square-wave generated in the ECM.
The earlier vehicles used a tach filter and filtered the tach signal from the coil firing waveform, which is conditioned, and this is passed to the ASR and tachometer.
Tom Piper
The '96 vehicles don't use a tach filter, the tach signal is conditioned square-wave generated in the ECM.
The earlier vehicles used a tach filter and filtered the tach signal from the coil firing waveform, which is conditioned, and this is passed to the ASR and tachometer.
Tom Piper
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 1,212
Likes: 0
From: OH
Yep thought about that, but don't have a tach filter in the system. I'm running a DelTeq, and before that was running MSD, both require removing of the tach filter. And when the filter is in the system you just don't get any tach.
I'm waiting a reply for the vendor. I can live with 1-200 rpm off, they aren't that accurate, but 1000 is unusable.
Is the tach movement dependant on the circuit board or the actual dial? If its just the board I could try swapping the dials on my units.
I'm waiting a reply for the vendor. I can live with 1-200 rpm off, they aren't that accurate, but 1000 is unusable.
Is the tach movement dependant on the circuit board or the actual dial? If its just the board I could try swapping the dials on my units.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by rsafier
Yep thought about that, but don't have a tach filter in the system. I'm running a DelTeq, and before that was running MSD, both require removing of the tach filter. And when the filter is in the system you just don't get any tach.
I'm waiting a reply for the vendor. I can live with 1-200 rpm off, they aren't that accurate, but 1000 is unusable.
Is the tach movement dependant on the circuit board or the actual dial? If its just the board I could try swapping the dials on my units.
I'm waiting a reply for the vendor. I can live with 1-200 rpm off, they aren't that accurate, but 1000 is unusable.
Is the tach movement dependant on the circuit board or the actual dial? If its just the board I could try swapping the dials on my units.
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Pro
Joined: Jan 2005
Posts: 686
Likes: 62
From: San Jose Ca
Originally Posted by rsafier
Yep thought about that, but don't have a tach filter in the system. I'm running a DelTeq, and before that was running MSD, both require removing of the tach filter. And when the filter is in the system you just don't get any tach.
I'm waiting a reply for the vendor. I can live with 1-200 rpm off, they aren't that accurate, but 1000 is unusable.
Is the tach movement dependant on the circuit board or the actual dial? If its just the board I could try swapping the dials on my units.
I'm waiting a reply for the vendor. I can live with 1-200 rpm off, they aren't that accurate, but 1000 is unusable.
Is the tach movement dependant on the circuit board or the actual dial? If its just the board I could try swapping the dials on my units.
