1991 5.3L 2500 Burb

Kelvin · Nov 20, 2020

I almost pulled the trigger on a 1 wire (smaller) oil sending unit to replace the factory ls sensor sense the ecm apperantly does nothing with oil pressure that I can see. Then as I was figuring out what I needed to do to bypass the 91 sensor it dawned on me i should keep it as GM intended. When oil pressure drops below 4 psi the fuel pump shuts down protecting the engine.

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swilson143 · Nov 23, 2020

I'll be watching this thread. I've got a 1991 V2500 5.7L 4L80E that I'm starting a 6.0L swap on next week. Bad news is I'm in CA, so I have to get refereed.

Nice job on the wiring! So tidy!

I didn't understand the end result on the above post... you're keeping the LS pressure sender? Will you be able to make the factory gauge work with it?

swilson143 · Nov 23, 2020

Kelvin said:
Gotta have that Factory AC.

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Can you confirm that is PART# 20-133 with spacer PART# 21-3?

Kelvin · Nov 23, 2020

No keeping the factory 91 sender with the fuel pump cutout in tact. That way my gage has the correct sensor and my engine has the low oil pressure protection by shutting down the fuel pump if pressure drops below 4 psi.
I lost an engine (ford) a long time ago when the oil pump drive off the distributor exploded so ive always worried about that.

Bextreme04 · Nov 23, 2020

You have to keep BOTH the LS sensors and the original engine factory 1-wire sensors for both coolant temp and engine oil pressure. The LS 3-wire sensors will go to the ECM for various functions and the 1-wire sensors will go to the factory gauge cluster only. You will probably need a "T" on the oil pressure sensor to accomplish that, but the coolant temp sensors will just be on either head, just like from the factory. My L29 454 has the single wire for the gauge located in the cylinder head, but has the 3-wire CTS to the ECU in the front of the factory intake manifold below the thermostat. No idea why it is placed there, but I'm going to leave it there. I would suggest leaving all factory LS sensors where they are also.

eskimomann209 · Nov 23, 2020

This is what I did for the gauge.

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TubeTruck · Nov 23, 2020

eskimomann209 said:
Someone’s a controls tech.

I said the same thing when I saw the Fluke sitting under the truck. Not everyone has them laying around.

Nice work man. I like seeing the progress. Gets me all excited to drop my engine in.

eskimomann209 · Nov 23, 2020

Right? Like who needs more than one?

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TubeTruck · Nov 24, 2020

eskimomann209 said:
Right? Like who needs more than one?

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Right? There's no need for that many

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eskimomann209 · Nov 24, 2020

TubeTruck said:
Right? There's no need for that many

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89Suburban · Nov 24, 2020

OP great progress there nice work.

Kelvin · Nov 25, 2020

You guys are nuts, those things are spendy but they sure last forever. That one under the truck is at least 20 years old.

Got the power distribution all finished up including relays and actually fastening the fuse box down now that I'm happy with where it will live. I haven't moved into the cab yet other than the diesel pedal and the OBD2 connector. I was looking at that unused cruise control servo and thought, well there's 5 wires I don't have to run through the firewall. And I hate seeing unused wires. I have plenty more of them than I wanted already. The other end of that plug goes to the cruise control module which I had to remove to fit the pedal. I looked over the schematics tonight and came up with a plan.

Cut the CC module plug off and solder

Tan---Brown
Dk blu/Wt---Grey
Lt blu/Blk---Dk blu
Lt Grn---Dk Grn

Find the DRAC and solder

***Note there are 3 brown wires on the drac. You want the one on the single connector***

Brn---Lt blu/blk

Now I have a nice place to connect wires from the TAC and a bonus VSS.

TAC to old servo wires
Grey---on/off---Dk blu/Wt
Dk blu---Set/coast---Lt blu/Blk
Gy/Blk---Res/Acc---Lt Grn
Yellow---VSS from ECM---Tan

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Kelvin · Nov 25, 2020

swilson143 said:
Can you confirm that is PART# 20-133 with spacer PART# 21-3?

Yes
Don't forget the corvette tensioner.
Link to a good writeup I used for this bracket if anyone in the future needs it.
http://www.ls1truck.com/forums/lsx-truck-conversions/47384-holley-ls-r4-c-bracket.html

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Kelvin · Nov 25, 2020

Bextreme04 said:
You have to keep BOTH the LS sensors and the original engine factory 1-wire sensors for both coolant temp and engine oil pressure. The LS 3-wire sensors will go to the ECM for various functions and the 1-wire sensors will go to the factory gauge cluster only. You will probably need a "T" on the oil pressure sensor to accomplish that, but the coolant temp sensors will just be on either head, just like from the factory. My L29 454 has the single wire for the gauge located in the cylinder head, but has the 3-wire CTS to the ECU in the front of the factory intake manifold below the thermostat. No idea why it is placed there, but I'm going to leave it there. I would suggest leaving all factory LS sensors where they are also.

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 · Nov 25, 2020

Kelvin said:
I almost pulled the trigger on a 1 wire (smaller) oil sending unit to replace the factory ls sensor sense the ecm apperantly does nothing with oil pressure that I can see. Then as I was figuring out what I needed to do to bypass the 91 sensor it dawned on me i should keep it as GM intended. When oil pressure drops below 4 psi the fuel pump shuts down protecting the engine.

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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?

1991 5.3L 2500 Burb

Kelvin

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swilson143

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swilson143

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Kelvin

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Bextreme04

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eskimomann209

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TubeTruck

I'm from Boston. Deal with it.

eskimomann209

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TubeTruck

I'm from Boston. Deal with it.

eskimomann209

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89Suburban

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Kelvin

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Kelvin

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bucket

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