Tach and speedo is not working after swap. Vehicle is a 91 Camaro 305 TBI Auto, to a 2004 CTS-V LS1/T56 using the 2004 PCM.

Tach is ran from Green 10 to C100 D6. Maybe because its a 2003+ PCM a resistor is needed? http://lt1swap.com/lsx_tach.htm

Speedo is ran from Green 50 to C207 Pin K (TBI), C207 to pin F of buffer box, pin f is connected (bypassed) to pin c of buffer box.

And I have no Speedo or tach, any thoughts or ideas are appreciated.

 

Ended up being an inconsistent battery ground to the neg terminal on the battery. Replaced the screw and got a good connection, speedo works fine.

Have not started to diag the tach yet, but I'm assuming we'll need to dig into the tach output mode in the PCM... I assume with a DBW motor its a 58x reluctor wheel? Not sure what number that will need to be for the tach to work...

 

To clear confusion, I was helping Chuck diag. his car. As stated above we have the speedo working, still looking into the tach not working.

 

Rule of thumb on tachs with LSx
No tach = need booster
Wrong tach = change PCM output

LS6 is still GEN III, so 24x reluctor, not that it changes anything

 

I am getting a "P0654 - Engine Speed Output Circuit" error code, not sure if thats due to not having a resistor or not. I've not checked for continuity from the PCM (Green 10) to the C100 (D6) yet, Ill try that tonight, assuming its ok then I'll get the resistor in.

How much voltage should I be getting at the C100?

Thank you for the clarification on the reluctor.

 

Whenever you get a code thats "blah blah circuit", its usually a wiring issue

Check continuity before trying the booster as camaros usually dont need it

 

Continuity is OK from PCM to the C100 for the tach. I'll try the resistor. Whats the best wire to jump it from? Ignition wire on the C100 (F4 pink)?

I sent Alan91z28 a PM with his LS3 swap and he did have to use a resistor for his Camaro (5k?), so maybe there's truth to the non-LS1 PCMs requiring it even in the Camaro.

Thank you

 

I use PCM ign fuse for the booster. 680ohm resistor

 

Put a 1k 1/4" resistor in place and the tach started moving, good news. I did rig it up to get it to work, just taped the resistor to a piece of wire, stuck the other side of the resistor in the PCM fuse, then connected the wire to the white tach wire behind the cluster. What's the right way to do this?

Sorry for the questions, this is my first jump into wiring even though I've been in IT for 10 years...

The error code went away too.

Chuck

 

Take two short lengths of wire and solder them onto the ends of the resistor

Use wire taps to clamp onto pins r10 tach and b19 PCM ign

 

Thank you a ton, Pocket. Getting a bouncing tach, and not rigged up. Time to get it tuned.

 

If the tune is indeed a 4cyl output, the tach should be steady. If it likes to jump from zero to xxx, it is either not enough booster or the tach is dying

Canaros have a removable chip that's easy to repair. My original tach in my bird crapped out around engine #3. Very strange because the same booster was used in all conversions