O2 sensor help (94 k3500)

[Road Trip]

I seen the diagram also you posted, but I was still confused on which is should be. I'm thinking single wire since it's a dually full size?

That's a pretty safe bet given that >8600 GVWR trucks were usually forced to meet
a relaxed emissions standard. (At least back then, things have since tightened?)

Going back to that diagram, if it was me I would look to see whether or not there's
already a tan wire at PCM pin A12? Assuming it hasn't been hacked by a PO in this
area, no tan wire = factory single wire. (matching >8600 rule of thumb for Federal
emissions. Cali emissions? YMMV)

Or, the tan wire *is* present, which would be the telltale hint that originally
the 3-wire HO2S were part of the original build.

Take a close look at your PCM, and let us know what you find.
(The PCM connector pinouts are definitely in the FSM, no guessing
required.)

Best of luck with the hunt. Glad you are focused on getting your truck correct
instead of how do I workaround/mickey-mouse my setup? :0)

Cheers --

 

[someotherguy]

Almost surely 1 wire based on manual transmission '94. Still uses the old ECM instead of the PCM for controlling an automatic; a lot of the automatic trucks got the 3 wire. My '94 C2500LD (350/4L60E) was 3 wire, where my '94 C1500 (350/NV4500) was 1 wire.

Placement can vary. Most 1 wire trucks had the O2 near the dump on the driver side exhaust manifold. Most 3 wire trucks have it in the exhaust pipe just before the catalytic converter. My '95 3500HD (7.4/NV4500) was 1 wire and it was down in the exhaust pipe before the cat.

Richard

 

[Road Trip]

Thanks ! I actually downloaded them yesterday. Saved this wide girl from going to the scrap yard. Was a work truck it's whole life, I can tell most of the work done on it was by people other then mechanics. Trying to un f' what everyone half assed. Knock sensor wasn't connected, coolant sensor wasn't connected. Currently battling a hard start / rough idle when warm. Replaced both temp sensors (redoing tho because I made mistake of using Teflon tape on the threads), replaced the IAC. Now trying to figure out the O2 sensor situation so I can get that sorted and better start to rule things out.

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NICE no-nonsense rig -- well worth getting all sorted out so that you can blow out the 'price per use' ROI metric
in your favor. (Insert golf clap here.)

By the way given that you are new here you may not be aware, but if Richard (someotherguy) replies
to your thread, do yourself a favor and pay close attention to his comments. He's been using the heavier
GMT400s for some time & he is one of the voices in here speaking directly from hard-won experience.

Nice photo of a nice truck. Looks more worn-in than worn out.

Good stuff.

 

[movietvet]

I seen the diagram also you posted, but I was still confused on which is should be. I'm thinking single wire since it's a dually full size?

The diagram covers both options.

 

[chris032188]

NICE no-nonsense rig -- well worth getting all sorted out so that you can blow out the 'price per use' ROI metric
in your favor. (Insert golf clap here.)

By the way given that you are new here you may not be aware, but if Richard (someotherguy) replies
to your thread, do yourself a favor and pay close attention to his comments. He's been using the heavier
GMT400s for some time & he is one of the voices in here speaking directly from hard-won experience.

Nice photo of a nice truck. Looks more worn-in than worn out.

Good stuff.

He does seem super knowledgeable. I'm going to go digging around tomorrow on my day off. I got the truck for a little over a grand, I figured the transmission is probably worth twice that. It also has a liftgate which wasn't working but I rebuilt that motor and got it working. I figured that too. It's probably worth close to what I paid. It also has a diesel transfer tank which I'll probably end up selling or converting it to gas to gas the boat at the dock.

I appreciate everyone's help. It's definitely a Time saver. I'm no mechanic but I do prefer to do my own work. I'm getting better. I do have some experience with the TBI because my boat has the GM system and I've had to do a lot of work on that.

I've already swapped out the bench seat for some buckets. I have some short legs so trying to get that clutch all the way in with the back seat was rough. I'm actually hoping there's a way to adjust that clutch or I'll be putting a block of wood on it

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[someotherguy]

By the way given that you are new here you may not be aware, but if Richard (someotherguy) replies
to your thread, do yourself a favor and pay close attention to his comments. He's been using the heavier
GMT400s for some time & he is one of the voices in here speaking directly from hard-won experience.

Thanks for the compliment but do be aware I'm often going on old memories and sometimes those memories aren't doing me (or others) any favors! So "trust, but verify" might be the best m.o.

Tearing my dash out last night in the '93 reminded me just how much of the little details I've forgotten over the past years of not working with these trucks every single day and night like I used to.

Richard

 

[someotherguy]

He does seem super knowledgeable. I'm going to go digging around tomorrow on my day off. I got the truck for a little over a grand, I figured the transmission is probably worth twice that. It also has a liftgate which wasn't working but I rebuilt that motor and got it working. I figured that too. It's probably worth close to what I paid. It also has a diesel transfer tank which I'll probably end up selling or converting it to gas to gas the boat at the dock.

I appreciate everyone's help. It's definitely a Time saver. I'm no mechanic but I do prefer to do my own work. I'm getting better. I do have some experience with the TBI because my boat has the GM system and I've had to do a lot of work on that.

Sounds like you scored a great deal! Most of these old work trucks have had some hacking that needs un-done. Once you get it sorted out it should prove to be a useful vehicle.

"Things could be worse"

Before

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After (yes, same truck)

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Richard

 

[chris032188]

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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[fancyTBI]

My ‘94 K2500 5.7/4L80e has a 1 wire O2. My ‘92 C1500 4.3/MG5 (as originally born with) had a 3 wire O2.

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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Those look like A/C related connectors. I’d get a photo of my ‘94 for you - but the whole harness is out. Does your truck have A/C?

 

[chris032188]

The truck had AC but previous owner removed it. I will be adding it back in down the road. Also to double check the temperature sensor on the top of the engine is for the computer and the side one is for the gauge, correct? I believe that the previous owner mixed up the two black wires and put the gauge wire on the top of the engine and The 1 one that goes to the top on the side. I'm wondering if this is part of the reason I'm having the hard start when the truck is warm