Fuel Trims Readings odd

Some back round, Over paid for a 1999 Chevy Tahoe 2dr, I have not drove it, because of brake problems (working on it when weather permits). I bought an OBDLinkMX+ to Log data. Looking at the data idling and up to temp the fuel trims are odd, long term are -15 both banks and sort term are close to 0, it also pops when I let off the gas after revving the engine. I also had the battery disconnected, not sure if that makes a difference on OBD2.
From what I been reading it could be a leaking fuel pressure regulator. I don't know what the fuel pressure is yet. New plugs, wires, cap, roter, and O2 sensors.

Is it normal for the long term trim to be so far off and the short term trim to be good?

Thank You Dom

not normal, but check you fuel pressure first.

Not normal but also not excessively bad either. Does it have anything other than a stock, original air cleaner system such as a cold air intake? I had a plastic pipe elbow and pipe to a K & N air filter that made the air through the mass air flow (MAF) sensor too chaotic. This drove my LTFT numbers in excess of +25 much of the time. It also did not help that I had over-oiled the K&N air filter such that excess oil was confusing the tiny MAF sensor wires. Some spray can stuff from a company called "CRC" with their Mass Airflow Sensor Cleaner took care of that.

But the biggest change occurred with me removing the plastic elbow and pipe and mounting the K&N cone filter straight onto the valve body. My STFT and LTFT numbers are now random values mostly plus or minus five.

Rick

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Originally Posted by Dom

Some back round, Over paid for a 1999 Chevy Tahoe 2dr, I have not drove it, because of brake problems (working on it when weather permits). I bought an OBDLinkMX+ to Log data. Looking at the data idling and up to temp the fuel trims are odd, long term are -15 both banks and sort term are close to 0, it also pops when I let off the gas after revving the engine. I also had the battery disconnected, not sure if that makes a difference on OBD2.
From what I been reading it could be a leaking fuel pressure regulator. I don't know what the fuel pressure is yet. New plugs, wires, cap, roter, and O2 sensors.

Is it normal for the long term trim to be so far off and the short term trim to be good?

Thank You Dom

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That's how trims work. LTFTs adjust to keep the STFTs close to 0.