Tach reading on 4X

[David_D]

Hi :-)

New to this forum and to HPTuners. Not new to LT1 tuning though.

I just did a 411 conversion on my 97 LT1 yesterday. Really easy swap since I am now running 4X (not 24X), just using the stock 4X reluctor wheel already on the crank.
Loaded a L31 file to PCM, with my own spark and VE tables.
Car fired right up and ran basically fine. But my tach reads way to low.

Tach output settings were as this:
Resolution High 6
Resolution Low 6

After reading threads on here I changed that to 3/3. Still almost no movement on the tach.

When I set the resolutions to 1/1, the tach reads 50% of the actual rpm. So idling at rpm 800, the tach shows 400.

That means that I would have to set the resolutions to 0.5/0.5 to make the math to match the 4X reluctorwheel to show the actual V8 signal.
But HPTuners doesn't let med put in 0.5 values.

Any suggestions ?
Thanks in advance :-)

[David_D]

In case someone else needs this in the future, here is the fix.

I bought a cheap tach adapter from ebay. No need for a fancy one with all kind of features. We only need the tach signal on this one.
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On the wiring loom to the cluster connector, there is 2 white wires (96-97 LT1 and 98 LS1 - They share the same pinout on the cluster).
One white wire is for the tach signal, and the other is for the Skip Shift Light, which I don't use anyway.
I cut one of the wires, and the re-attach the cluster and start the car. If the tach still works, you need to cut the other wire. We need to work on the white tach signal wire.
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Then solder the correct color wires for your tach adapter, to the white wires
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I put the tach adapter in that whole and reach it from underneath the dash
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From here it is very easy to solder the 2 remaining wires to a ground signal, and an Ignition +12V source. I already had a fused ign wire, so I just spliced it in there.
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Then I used som zip cable ties to hide things away, started the car and the whole thing was now spot on :-)
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