I’m going to be doing a V8 swap into my 87 GT. I’m going to be using the LS4 out of a complete donor car. Was wondering how difficult it is to get the stock gauges to work after the engine swap.

if you are you using the fiero transmission the speedometer will work.use the fiero oil and temp senders.the tach is more complicated.

With the condition I found the motor in I didn’t trust using the transmission so I’m fully swapping engine and trans. Was really hoping not to lose the stock gauge cluster.

[This message has been edited by CjMatthews (edited 05-12-2025).]

You can retain all factory gauges. It just takes planning and addressing each one individually.

Speedo will go to the ECM, then to the fiero cluster and will need a stepper circuit.
Tach will come from the ECM and use a stepper circuit.
Use the 3-wire temp gauge from an early LS1 Camaro. The 3rd pin will run the temp gauge.
Add the FIero oil pressure sender to the LS4 to run the stock oil gaige.

quote Originally posted by CjMatthews: I’m going to be doing a V8 swap into my 87 GT. I’m going to be using the LS4 out of a complete donor car. Was wondering how difficult it is to get the stock gauges to work after the engine swap.

Just to iterate what is kind of already known by some (but not totally obvious who hasn't done this before), the nice thing about most 80s GM cars is that the gauge clusters are totally independent of the engine computer. Like for example... your stock V6 will have three temperature sensors... or really, four. One is a coolant temperature sensor that controls when the fan turns on, one is an intake air temperature sensor, another is a coolant temperature sensor that tells the computer what the temperature is, and then there's a separate temperature sensor (sending unit) that tells the gauge cluster what the temperature is.

So when you do the engine swap, all you need to do is make sure that all the existing gauges have their respective sensors connected to something:

- Temperature Sensor (find a bung or place to screw in the gauges temperature sensor and you're good)
- Voltage Gauge (I think off the alternator?)
- Oil Pressure (use the V6 Fiero oil pressure sending unit)
- Speedometer (uses the transmission's VSS)
- Tachometer ... you'll need a tach signal, depends on the engine you're using.


otherwise, it should not be an issue at all...

The Cajun Tach Shop can set you up with a new replacement board calibrated for a V8

Forum member JGunsett repairs, recalibrates and restores the factory gages for a very reasonable price.