1991 5.3L 2500 Burb

[Bextreme04]

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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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.

 

[Kelvin]

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?

Funny you brought that up. I drew up the diagram last night just so I could wrap my head around it and came to the same conclusion. I settled on the avalanche 1 pin sender and the ict 16mm blockoff plate because the 91 sender is 1/4" npt. Hopefully its still a 90 ohm sender.

All stock for now, I started this a while back and sense then we've bought a much larger camper. I borrowed my brothers 99 dodge with a Cummins to pull it home and realized the 5.3 isn't going to cut it.

 

[Kelvin]

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.

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.

 

[Kelvin]

https://www.ebay.com/itm/LS-Swap-Coolant-Temp-Sensor-and-Harness-/264486248035

And for 60$ this guy takes all the guesswork out of it. I should have just bought this one from the beginning and been done with it.

 

[Bextreme04]

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.

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.

 

[bucket]

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.

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.

 

[Bextreme04]

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.

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.

 

[bucket]

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.

Right, we are on the same page. It's just terminology. I used to frequent a forum for GM's 60° V6 and everyone there called it a "3-wire temp sensor", not to be confused with other sensors that would usually employ a 5v reference.

 

[Kelvin]

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.

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.

 

[bucket]

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.

Adding in a resistor is actually a GM approved repair for a gauge that read too high, which I guess was a common customer complaint in the 90's. I only ran into that issue a couple times myself. All I did was wire in an adjustable resistor and tweak it until the gauge had the same reading as what the ecm was was showing on the scanner. It was simple and worked.

 

[Kelvin]

Now where did I leave off? It runs!
I've driven it probably 20 miles and already did the MAF tuning.Driving across the river without exaust to rhe muffler shop was fun but its super quiet now. In my garage I couldn't get it above 145 degrees and remembered I never did replace the thromostat. Im not sure the old one was bad because even with a new one it took a good bit of driving to get it up to temp. The 2500 Suburban radiator is a pretty heafty unit so that probably acounts for some of that. The transmission shifts really harsh. Ive just learned of the changes in 1994 to a different pressure control solenoid amongst a couple other changes. I spoke with a couple transmission shops and they both said put the newer style solenoid in so I found 1 from an 05 along with the harness because the plug is different. The other changes that year are they deleted and accumulator as it isn't needed will the newer programming ( no spikes from the cleaning cycle). I figure leaving it (the accumulator) in there shouldn't matter. There was 1 hole deleted from the spacer plate. Ill research why soon and if needed find that newer plate. I almost got the whole valve body for a steal but then we realized the oil lines make it not compatible.

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[Kelvin]

Would have rather edited the first post with this info but I can't figure it out. Here is a list of parts I used from Amazon. Everything else was purchased from my local napa except the drivers side battery tray from LMC truck. https://www.amazon.com/hz/wishlist/ls/2JTX2T6NHCWZ6?ref_=wl_share