I'm planning the typical TBI to carb swap, I've read the tech. article and I've looked up what I can in here, but still there's some gray areas in between.

Edit: Car is a 1988 Iroc-Z TBI.
When I pull the computer and engine harness, I know I'll be separating out wires to be kept (i.e. alternator, two distributor wires, starter, etc.). I would like for the Instrument cluster to work as normal, but do not know how removing the coolant temp. sensor will affect this.

One, which coolant sensor should I keep, passenger cylinder head or intake?

Two, How does the gauge function from the sensor; does the sensor send a signal to the ECM and the ECM relays it to the instrument cluster, or does the ECM receive the signal from the guage?

Three, how will the fuel pump be affected?

Four, same question as two, except applied to the oil pressure sender.

I know these questions are difficult and most times do not get responded to on here, but any input (as long as its factual, lol) is much appreciated. Thank you.

 

my 87 305 had one hrness for ecm one for gauge cluster i just puld the wiring harness from the ecm pulled it out through the fender and went from there the started and such were in my other harness i didn't pull that went to the driver side of the engine compartment i just used the coolant temp sensor in the intake as a plug for now its not hooked up and i still get a reading to my gauge so keep the one in the head its for the gauge as for oil i dunno mine stopped working when i did it so i installed a aftermarket one..one thing i dont know is about the cooling fans cause i think the ecm controls them something i havent really looked into yet,but thats for my 87 305 carb set up dont know if you 88 TBI will be the same but on mine everything i wanted and needed was wired into the fuse box side of the car...hope this helps

 

1) Correct, the sender in the head runs the gage.

2) It sends a power signal to the sender, in series with the gage. The sender decreases the resistance to ground as the coolant gets warmer. If you touch the wire to ground with the switch on, the gage should peg hot. The gage and the ECM don't talk to each other. The "coolant temperature sensor", the 2-prong weather pack connector, is a 5-volt signal from the ECM back to the ECM.

3) The fuel pump relay is powered by the ECM. You'll need to wire the relay to a switched power source. There is a parallel source through the oil pressure sender/switch.

4) Oil pressure sender works similar to the temp gage. The higher the oil pressure, the less resistance to ground. Ground the wire directly, and the gage should peg high.

 

Did this to my 92 a while back. Oil and temp senders as noted above. Also, you can re-cycle the power and tach connections easily if you go to an earlier non computer controlled large cap HEI (factory tach will still work).

I didn't remove my computer. I liked having it run the fuel pump to prime it for 2 seconds when the key was turned on. And in my case I needed it to run the speedo as well (no speedo cable in the 90-92 cars).

End of the day, everything on the dash worked just like it did before, just that the check engine light was on solid (obviously). A/C still worked, too, because the ECM has nothing to do with it.

 

thought the electric speedo ran off the yellow buffer box by the ecm? cause my ecm is gone and speedo still works

 

i feel the need to point out on this old thread that the 91-92 have an electric speedo and previous models have a cable driven one.