Fuel Trim

g2full · November 6, 2019

Alright, I'm lost.

Anyone local to York, PA with a scan tool that would be willing to meet up? Or have an idea of where to go next?

I'm trying to chase down a negative fuel trim issue on bank 2 of my 15 silverado 5.3.

MAF was lazy, replaced that. Which took me from a -20% fuel trim at idle to -13%. Injector Pules on Bank 1 are solid across the board however pulses on bank 2 are all over the graph.

None of my scan tools will dial in above 2013.

davester · November 6, 2019

don't live anywhere nearby, but you may want to check for an exhaust leak between the engine and the upstream O2 sensor on that bank...or an intake leak...

CamGTP · November 6, 2019

Negative fuel trims generally means extra fuel. Positive trims would be an exhaust/vacuum leak because of the extra air.

I would swap o2 sensors side to side. If the issues jumps to the drivers side, then the o2 sensor is reporting incorrectly.

g2full · November 7, 2019

2 hours ago, CamGTP said:

Negative fuel trims generally means extra fuel. Positive trims would be an exhaust/vacuum leak because of the extra air.

I would swap o2 sensors side to side. If the issues jumps to the drivers side, then the o2 sensor is reporting incorrectly.

Upstream and downstream sensors? Or just the downstream? Looking at those on the scanner they appear to be tracking properly, but doesn’t mean they aren’t skewed.

I should have added that this fuel trim issue was discovered when the truck went in for lifter and pushrod replacement. No idea how long it’s been this way because it isn’t setting a MIL. But, it still isn’t right.

Jmanson6262 · November 7, 2019

Is your truck a flex fuel. I had similar issues with my 08 tahoe. Ended up being an algorithm issue with the flex fuel virtual sensor needing to be reset. It was reading 56% ethanol and throwing off my trims but only on 1 bank.

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g2full · November 7, 2019

9 minutes ago, jamisonericksen said:

Is your truck a flex fuel. I had similar issues with my 08 tahoe. Ended up being an algorithm issue with the flex fuel virtual sensor needing to be reset. It was reading 56% ethanol and throwing off my trims but only on 1 bank.

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Non flex model.

Jmanson6262 · November 7, 2019

So bank 2 injectors all over the place? Perhaps a leaky injector. Maybe check fuel pressure key on engine off. Should read around 55psi. That's all I got for now.

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g2full · November 7, 2019

9 minutes ago, jamisonericksen said:

So bank 2 injectors all over the place? Perhaps a leaky injector. Maybe check fuel pressure key on engine off. Should read around 55psi. That's all I got for now.

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Will check that. I know on my scanner I can pick up fuel rail pressure, but there’s a lot I can’t do. I’m reading the truck as a 13 5.3 LC9 motor. I figure it might not be 100% accurate but it’s what I have access to.

If I can figure it out I will post a video tomorrow of both injector banks pulses.

CamGTP · November 7, 2019

You would swap the upstream o2 sensors. The downstream o2 sensors only report how the cat converter is doing.

The value the trims are pulling won't set a code because it's withing the range or normal operation.

You can't check fuel pressure like you want to. Your 2015 truck uses direct injection. A scan tool will show you the low pressure fuel pump readings and the high pressure fuel pump is under the intake manifold that is operated by a lobe on the camshaft to raise the fuel pressure to up around 1,800-2,500psi. Again a scan tool would be needed there to read that pressure.

Your engine is also a L83. The LC9 is the GEN 4 port fuel injected engine from the previous model trucks. So if your scan tool can't read the truck as a 2014+ engine, possible many of the watched parameters will be wrong in reporting back data.

Jmanson6262 · November 7, 2019

That's right, my apologies. I forget we are dealing with direct injection. Yeah o2 swapping might be the best bet at the moment.

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g2full · November 7, 2019

26 minutes ago, CamGTP said:

You would swap the upstream o2 sensors. The downstream o2 sensors only report how the cat converter is doing.

The value the trims are pulling won't set a code because it's withing the range or normal operation.

You can't check fuel pressure like you want to. Your 2015 truck uses direct injection. A scan tool will show you the low pressure fuel pump readings and the high pressure fuel pump is under the intake manifold that is operated by a lobe on the camshaft to raise the fuel pressure to up around 1,800-2,500psi. Again a scan tool would be needed there to read that pressure.

Your engine is also a L83. The LC9 is the GEN 4 port fuel injected engine from the previous model trucks. So if your scan tool can't read the truck as a 2014+ engine, possible many of the watched parameters will be wrong in reporting back data.

Yeah, I was worried about mis read data due to that. I just don’t have access to anything to read 14+.

23 minutes ago, jamisonericksen said:

That's right, my apologies. I forget we are dealing with direct injection. Yeah o2 swapping might be the best bet at the moment.

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That sounds like my next step. Will report back when I find something.