Closed loop issue's

So after some looking around Ive seen some limited folk with some of the same problem im running in to.

Quick run down on what i've got.

86 c10 5.3 swap with 4l60
Medium cam 600ish lift 112 lsa bla bla bla
Amazon's finest sheet metal intake money can buy!!
Longtube's to x-pipe with some spintech 3000 series mufflers
Speedmaster dbc standalone harness
00 Silverado dbc pcm
ls3 injectors
2200 stall converter i think??
Maybe a few other lil small things but ya get the picture.. Mild build.

Problem is 02's are not sampling. They hang at 450ish mv with very little movement. 3-5 mv. Pcm will not go in
closed loop. Keep getting fuel system ol fault. I have ohm'd the loom from pcm to o2's with success. Both high and low
signal's are checking out. Heater circuit is fine along with the common ground. Was hoping someone-someone's have
had this issue and can point me to the fix!!

Means you have bad 02s or wiring to 02s is messed up… see this all the time

o2's have been replaced with new denso's then new ntk's. I continuity/ohm tested all o2 wires between pcm and o2 sensors. High/low reference, heater circuit, and ground. All check out. ???

What wiring harness? Name brand aftermarket or self modified OEM?

Speedmaster aftermarket... Yet it most likely is just a cheap china harness reboxed. I own several of those china units and have had hit or miss results.
So i tried a "name brand ish" harness to see the quality differences and im not impressed.

Mitch at swaptime does some of the best harnesses I've seen and if something is wrong he'll usually help walk you through diag and fix it. As of late he's even started using a lot of the OE wiring colors.

I would recommend finding a schematic for what the ecm is programmed to then back tracking pins for powers and grounds along with the correct signal voltages.

Quote:

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Originally Posted by InandOutPerfromance

o2's have been replaced with new denso's then new ntk's. I continuity/ohm tested all o2 wires between pcm and o2 sensors. High/low reference, heater circuit, and ground. All check out. ???

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Continuity test to the PCM is meaningless if the wire harness is pinned wrong at the computer. This is extremely common.

Can't go wrong with PSI harnesses. What O2 are you using. You said 00 Silverado PCM. There were 2 styles used that year. Do yours have flat 4 pin connectors or square 4 pin connectors?

Quote:

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Originally Posted by 2xLS1

Can't go wrong with PSI harnesses. What O2 are you using. You said 00 Silverado PCM. There were 2 styles used that year. Do yours have flat 4 pin connectors or square 4 pin connectors?

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Aftermarket harness from speedmaster. Harness has male square o2 plugs.

When i was testing i was testing harness. I looked up pinout for a 00 silverado and from what i can find the high/low signal are 26/29 and 66/69 and those match the harness i have.

The 450mv O2 scanner reading is an open circuit default value. It is most likely wired incorrectly. Especially if it's the same with multiple replacement sensors.

Quote:

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Originally Posted by InandOutPerfromance

So after some looking around Ive seen some limited folk with some of the same problem im running in to.

Quick run down on what i've got.

86 c10 5.3 swap with 4l60
Medium cam 600ish lift 112 lsa bla bla bla
Amazon's finest sheet metal intake money can buy!!
Longtube's to x-pipe with some spintech 3000 series mufflers
Speedmaster dbc standalone harness
00 Silverado dbc pcm
ls3 injectors
2200 stall converter i think??
Maybe a few other lil small things but ya get the picture.. Mild build.

Problem is 02's are not sampling. They hang at 450ish mv with very little movement. 3-5 mv. Pcm will not go in
closed loop. Keep getting fuel system ol fault. I have ohm'd the loom from pcm to o2's with success. Both high and low
signal's are checking out. Heater circuit is fine along with the common ground. Was hoping someone-someone's have
had this issue and can point me to the fix!!

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yes i had that problem myself and found out they sold me sensor 2 instead of sensor one and my mv stayed at 450 like yours and would not go into closed loop make sure you have sensors 1 installed air/fuel sensors sensors 2 will not work there only for catylst eff.

There is also something about grounded and non grounded o2 sensors. I don't know for sure but blindsquirrel has talked about it.