1991 5.3L 2500 Burb

Kelvin said:

You could have tapped into the green wire on your 3 wire for your temp gauge same as I could have run 1 extra wire to the front and swapped my 2 wire for a 4 wire firebird sensor. It was just easier to separate them as the gauge wire was already in the right spot (pass rear) so im using the firebird sensor and plug but only the center pin on it. The center pin or green wire is the resistance wire. The other two require 5v reference and signal return for the ecm. After attempting to remove the factory oil pressure sensor I decided to leave that pain in the butt in there and run the factory one off the oil filter plate same as the rest of the saine people on here.

Did all the interior wiring today. Really didn't want to pull the dash but I caved. So after a full day in mostly awkward positions and fixing alot of unrelated wiring from the PO, I can safely say the inside is done...well, I still gotta put the dash back together.

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bucket said:

Look at the diagrams again, that's actually not how it works. Yes, GM usually had the fuel pump circuit tied to an oil pressure switch. But that oil pressure switch actually supplies power to the pump circuit, in the event of a fuel pump relay failure. Even without knowing how GM did it, this is obvious to me based on all the people I've seen kill a GM engine from having no oil pressure, lol.

So is this a stock 5.3 you are using or are there tweaks?

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Bextreme04 said:

That’s definitely not how that coolant sensor works. You are not going to get a useable coolant temp reading for your gauge from a 5v reference sensor. The 3 wire 5v reference and 1 wire resistive sensor work on completely different principals and won’t provide a usable signal to a gauge. You will have 5v power, ground, and ref on that 3 wire. The ref signal is a power output(from the sensor) that varies from 0-5v as the temperature changes and is read by the ECU. The gauge works by supplying power from the gauge, through the sensor(with varying resistance based on temperature) to ground. This means that with your gauge wire spliced to ref, not only are you not going to be providing a variable resistance to ground, but you will be pushing 12v through your 5v ref signal wire and could quite possibly smoke your ECU or sensor(since it is only designed to handle 5v).

your gauge would also be seeing the circuit as an open at the same time, which would mean it would be locked on cold. The ECU would be seeing the same thing, since the voltage would always be 12v, so if it doesn’t blow, it’s going to at-best throw a sensor voltage circuit code and at worst just think it is always freezing cold without throwing a code.

The way the 2 wire circuit is designed is different, and you could probably get away with a splice, as long as you diode protect the ECU circuit so that you aren’t feeding 12v back to the ECU. I still doubt the 2 wire sensor would provide a correct resistance profile to match the gauge though.

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Kelvin said:

https://ls1tech.com/forums/conversi...e-coolant-sensor-conversion-part-numbers.html

Bextreme go read through this and see if I'm interpreting it wrong but my understanding is this specific part is a 2 wire "sensor" and a 1 wire "sender" in 1. 1998 would be the time frame of when the PCM needed a sensor but they still replied on an anolog gauge. 2002 I believe GM went straight to ECM telling the instruments what to display.

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Bextreme04 said:

The way I read that is that the 98 Firebird had a 2 pin 5v reference sensor and 1 wire sensor all in one. It was not a 3-wire 5 volt reference sensor. My 97 L29 had a 3 wire 5v reference sensor for the ECU and a 1 wire sensor in the head for the gauge. If you are converting an LS that never had a analog gauge and used a 2 wire sensor to begin with, you can convert to that specific gauge and get the same effect(maybe) as just using the stock LS gauge for the ECU and keep the original engines 1 wire gauge sensor with an adapter into one of the heads. I say maybe because there is no guarantee that the resistance curve will match the curve expected by you coolant temp gauge. Its guaranteed to match if you use the original sender for the gauge. You cannot splice into a regular 2 wire or 3 wire 5 volt reference for a gauge though.

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bucket said:

That sensor pictured, I would call it a "three wire temp sender". The same type of sender was used in a lot of mid-late 90's GM cars (primarily fwd) except they were NPT rather than that metric thread with a washer. They simply combine a CTS and a gauge sender all in one.

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Bextreme04 said:

The one listed in that linked thread on LS1tech is definitely a 3-wire, but I think where we have a misunderstanding here is with the 5v reference sensor thing. I just went out and looked at my setup again and it is a 2 wire sensor not a 3-wire for the ECU. My engine did have a separate 1 wire sensor for the gauge though. The linked sensor is absolutely not a 3-wire 5v reference sensor. It is basically a combined 2 wire 5v reference and a standard 1-wire gauge sensor. There are actual 3-wire 5v reference ECT sensors that would work very different than this, which is why I made that statement.

While it looks like this would work just fine without smoking either the gauge or the ECU, I would still recommend you measure the resistance of the 3-wire sensor and your original vehicles single wire sender across multiple temps to make sure your gauge will still read right with the new sensor. Just because the signal type is compatible, doesn’t mean the resistance range will be. I believe there were at least three different resistance range gauges that worked with different sensors.

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Bextreme04 said:

The one listed in that linked thread on LS1tech is definitely a 3-wire, but I think where we have a misunderstanding here is with the 5v reference sensor thing. I just went out and looked at my setup again and it is a 2 wire sensor not a 3-wire for the ECU. My engine did have a separate 1 wire sensor for the gauge though. The linked sensor is absolutely not a 3-wire 5v reference sensor. It is basically a combined 2 wire 5v reference and a standard 1-wire gauge sensor. There are actual 3-wire 5v reference ECT sensors that would work very different than this, which is why I made that statement.

While it looks like this would work just fine without smoking either the gauge or the ECU, I would still recommend you measure the resistance of the 3-wire sensor and your original vehicles single wire sender across multiple temps to make sure your gauge will still read right with the new sensor. Just because the signal type is compatible, doesn’t mean the resistance range will be. I believe there were at least three different resistance range gauges that worked with different sensors.

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Kelvin said:

I can't remember where I read it now but I remember someone saying the range was linear and if the range was off we could just add a resistor to bring it back to the correct range. I may set up a science experiment in the kitchen involving both sensors when the wifes not looking.
Minor details, hope to make some progress on the rest of the setup tomorrow. Ive slacked off for Thanksgiving long enough.

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