O2 sensor help (94 k3500)

[fancyTBI]

Single wire goes to the temperature sending unit in the drivers side head which controls your gauge.
The two wire temperature sensor is on the intake manifold. In most cases on less-modified vehicles there will be a two wire (black and tan) ground on a ring terminal on a stud shared with the thermostat housing hardware. This ground is for your temperature sensor. Verify that this is clean and the wires aren’t weak.

This could be part of your hard start problem. I can’t remember the exact scenario for this, but in certain instances if the ground or sensor is bad (or just plain hooked up wrong) the computer thinks it is -40° and way over compensates.

I’m not dead set on the -40° figure, I should check the manual.

 

[chris032188]

Single wire goes to the temperature sending unit in the drivers side head which controls your gauge.
The two wire temperature sensor is on the intake manifold. In most cases on less-modified vehicles there will be a two wire (black and tan) ground on a ring terminal on a stud shared with the thermostat housing hardware. This ground is for your temperature sensor. Verify that this is clean and the wires aren’t weak.

This could be part of your hard start problem. I can’t remember the exact scenario for this, but in certain instances if the ground or sensor is bad (or just plain hooked up wrong) the computer thinks it is -40° and way over compensates.

I’m not dead set on the -40° figure, I should check the manual.

Yeah I noticed that the wires going to my temperature sensor at the top of the engine were spliced and a new connector was tied in. But when I grounded that connector it made the temperature gauge move which makes me believe that they mixed up those two black wires.

 

[chris032188]

I just picked up a scanner driving home now so I'll let you know about the figure when I hook it up to the truck

 

[Road Trip]

This could be part of your hard start problem. I can’t remember the exact scenario for this, but in certain instances if the ground or sensor is bad (or just plain hooked up wrong) the computer thinks it is -40° and way over compensates.

I’m not dead set on the -40° figure, I should check the manual.

You got it right. chris032188 had added a question to an older dead end thread with similar symptoms,
and I just replied with the links to a successful troubleshooting session involving a bad sensor misleading
a good computer earlier this year. (-40° fueling leads to hard starting when warm)

It's all in there somewhere. :0)

 

[chris032188]

Got o2 sensor in looks like the Barrell connector was on a purple wire. It's reading on scanner so I think it's right. A portion of my harness that's in that loom was ripped (I think it got caught on drive shaft. I'm repairing that now. Just patched speedo sensor but I see some more wires and a bare wire (this was in same tight wrapped peice speedo was in). It looks a light green and blue together, and a black with white stripe by itself. Anyone know what these are for? I don't see anything under here they could run to

 

[Zaeea]

Found the O2 connector dangling under truck next to some ripped wires I had. I have these 3 open connectors up top - anyone recognize them?

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Middle pic is definitely the connector that goes to a pressure switch in the back of your AC. Just installed a Sanden upgrade on my 99 burb cause the OEM compressor seized and took out the tensioner pulley along with it.

That red connector almost certainly goes to the AC condenser

 

[Road Trip]

Yeah I noticed that the wires going to my temperature sensor at the top of the engine were spliced and a new connector was tied in. But when I grounded that connector it made the temperature gauge move which makes me believe that they mixed up those two black wires.

FWIW here's the wiring diagram between the ECT & your computer according to the '94 FSM:

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This should be pretty straightforward to verify where your truck is deviating from this diagram.

NOTE: If you find the root cause of this and you can get a clear photo of what the PO did in order
to cause the problem, please take the shot & post that here along with a description of what you
uncovered. TIA --

 

[chris032188]

FWIW here's the wiring diagram between the ECT & your computer according to the '94 FSM:

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This should be pretty straightforward to verify where your truck is deviating from this diagram.

NOTE: If you find the root cause of this and you can get a clear photo of what the PO did in order
to cause the problem, please take the shot & post that here along with a description of what you
uncovered. TIA --

It's fixed, connection was bad that PO spliced in.

 

[chris032188]

Now I'm into the next problem, looks like portion of wiring harness to speedo got wrapped up in drive shaft and ripped out. Got that fixed trying to figure out these other wires - lightish blue and like green, black white stripe, and there's what seems to be a bare metal wire wrapped with the purple and green for speedo. Trying to find these on manual now. I don't see anywhere under truck yet they could go

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[Road Trip]

Just patched speedo sensor but I see some more wires and a bare wire (this was in same tight wrapped peice speedo was in). It looks a light green and blue together, and a black with white stripe by itself. Anyone know what these are for? I don't see anything under here they could run to

I think I found a match in the '94 Electrical FSM for the Lt Green / Blue combo. Q: Are your backup lights operational?
Is there anything connected to that switch in your manual trans?

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This seems to be pretty good possibility given the area that you are working.