Another 454 Vortec Build Thread - Documenting, Q&A, Help

Looks all whack to me but im not exactly an expert.

Bank 1 STFT is about +15.63%
Bank 2 STFT shows -1.52%.
They should be nearly the same and ideally under 10%
Bank 2 Sensor 2 shows nothing
Calculated boost should be showing 0 i believe.

Ugh not good. I’m 100% thinking this is related to the missing rear O2 sensors and the no exhaust after the manifolds. There’s only about 1ft of pipe. Can anyone share a stock 454 screenshot of these sensors?

Bachert24 said:

Ugh not good. I’m 100% thinking this is related to the missing rear O2 sensors and the no exhaust after the manifolds. There’s only about 1ft of pipe. Can anyone share a stock 454 screenshot of these sensors?

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Rear O2 sensors have nothing to do with fueling. Lack of exhaust will definitely screw with the front O2 sensor readings. You need 15" or so of exhaust past the O2 sensor to keep it from reading ambient air and getting all out of whack.

You probably also have an intake leak somewhere based on how out of whack it is side to side.. but you probably won't know for sure without a smoke test or until you get some exhaust on it. I wouldn't worry about the rear O2's until you get a full exhaust with cats on it installed. If you don't get cats installed, you don't need the rear O2's at all.

BeXtreme said:

Rear O2 sensors have nothing to do with fueling. Lack of exhaust will definitely screw with the front O2 sensor readings. You need 15" or so of exhaust past the O2 sensor to keep it from reading ambient air and getting all out of whack.

You probably also have an intake leak somewhere based on how out of whack it is side to side.. but you probably won't know for sure without a smoke test or until you get some exhaust on it. I wouldn't worry about the rear O2's until you get a full exhaust with cats on it installed. If you don't get cats installed, you don't need the rear O2's at all.

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thank you sir! Installing an exhaust this weekend then will check again and see what it looks like. Hopefully not an intake leak but very well may be as the bottom side of the heads above the manifolds look somewhat damp from oil or potentially coolant.

Short video of the live data. If anyone sees anything out of whack let me know. Not sure if I used the correct protocol since lots of sensors are absent so I'll looking for another app.

Bachert24 said:

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Short video of the live data. If anyone sees anything out of whack let me know. Not sure if I used the correct protocol since lots of sensors are absent so I'll looking for another app.

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Unfortunately it says I need access.

454C2500Longbed said:

Unfortunately it says I need access.

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Try it now

I have seen the fueling do that in multiple instances. Every one was a dead cylinder on the bank with the maxed out fuel trims. Bank 1 is at maximum fuel adapt richer. Look for a cylinder that is not firing. Cracked or fouled plug, burned spark plug wire, bad distributor cap, or an injector that is not functioning. I would be looking for a dead hole on the LH side of the engine. Cylinders 1, 3, 5 or 7.

Adding to what L31 said, the O2 sensor only reads oxygen content. So an intake leak will read lean to the sensor(but probably only a small amount), an exhaust leak will also read lean(proportional to the size of the leak and a large enough leak to cause a maxed out trim should be audible), and lastly a misfire will almost always max out the sensor to the lean side. This is because no combustion occurred, so ALL of the air that entered the cylinder is still there. You can also get high rich trims like this if you have no exhaust. You need to have at least 18"(preferably twice that) of pipe after the sensor to keep air from traveling back up the pipe and throwing off the reading.

I should give more info in order for you to lead me in the right direction. I just put in new plugs, wires, cap, rotor, FPR, injectors. The exhaust was hacked off 12" after the manifolds and now has new cats, about 4 ft of exhaust pipe, and then 2 new mufflers...so a total of about 6' of exhaust currently. Also has a new fuel pump. With all that being said what direction do you think I should look? Is there an easy way to tell if the LIM gasket is bad without pulling the UIM? Its a cheap fix so I will do it if needed but i dont want to pull off parts if i dont have to. Unfortunately the code scanner doesnt read cylinder misfires on this vehicle like it does my 2010 Equinox.