Extreme negative LTFT's.

Bedwards923 · November 10, 2021

Hi all. I have a 2018 Silverado LT with the 5.3L with 58500 km on it. The truck has had several exhaust leaks, which the dealer has rectified under warranty (passenger side manifold replaced, as well as the manifold/downpipe gaskets on both sides). An upstream O2 sensor was also replaced, as it was failed after my first dealer visit. Under light acceleration, I can still hear a very minor "tick," but the dealer has assured me they have inspected the exhaust system and found no leaks. I recently bought an OBD2 scanner, and I've noticed that my LTFT's are extremely low negative numbers. At idle, I have seen as bad as -25%, but it usually hovers around -17% to -22%. While driving, it is generally around -13%, but sometimes it's lower than that. I am getting these numbers on both banks (sometimes one bank is like 2% difference). The dealership said the throttle body air flow compensation value was at 67%, so they cleaned the throttle body and did an idle relearn. Compensation value is now 0%. I have also cleaned the MAF sensor, and tried blocking off the EVAP purge solenoid vacuum line to see if it changes the fuel trims, but they are still the same. The air filter is clean and basically brand new. I've never dealt with negative fuel trims before, and I am kind of at a loss of where to go. I've heard of these trucks having problems with the high pressure fuel pump, but I'm not sure how to really diagnose and confirm that. Any suggestions or advice would be much appreciated!

M1ck3y · November 10, 2021

The ticking is from the injectors. Fuel trims are normal.

CamGTP · November 10, 2021

1 hour ago, M1ck3y said:

The ticking is from the injectors. Fuel trims are normal.

-25% on the fuel trims is not normal for idle and neither is negative 13 to 20% while driving.

Is this a flex fuel truck? If it was I'd be curious as to what the alcohol content the truck is saying it is.

M1ck3y · November 10, 2021

5 minutes ago, CamGTP said:

-25% on the fuel trims is not normal for idle and neither is negative 13 to 20% while driving.

Is this a flex fuel truck? If it was I'd be curious as to what the alcohol content the truck is saying it is.

My truck had similar ltft right before I had it tuned.

CamGTP · November 10, 2021

Never saw that with mine or the other GEN V trucks I've tuned.

Bedwards923 · November 10, 2021

7 minutes ago, CamGTP said:

-25% on the fuel trims is not normal for idle and neither is negative 13 to 20% while driving.

Is this a flex fuel truck? If it was I'd be curious as to what the alcohol content the truck is saying it is.

It is not a Flex Fuel truck. The dealership said there was no fuel alcohol reading on the scan tool when it was checked today.

M1ck3y · November 10, 2021

I can't speak for the op, but my fuel trims were a result of climate. When it's in the -30's the truck goes through an insane amount of fuel.

Doublebase · November 15, 2021

-20 through -25 is what I was experiencing on my 2018 with 45,000 absolutely babied and well maintained miles.

I never knew if it was "normal" or not - only reason I even took a look is because of a cylinder number 5 misfire - which I never pinned down a reason for...random misfire, everything seemed ok. However I'd experience a misfire/shudder event when climbing a hill at highway speeds. I ended up trading it in at 50,000 miles - I think what finally did me in was the reports of fuel injector issues - that, and knowing that they were no longer covered under warranty. And I didn't like the fact that I had purchased a new truck and it couldn't make it up an incline on a highway without stuttering. Problem started at around 37,000 miles.

also pulled the pan on the transmission, thinking it was a tranny/torque converter issue, but everything looked good in there...no metal, nothing. Changed filter and fluid, no improvement.

M1ck3y · November 15, 2021

1 hour ago, Doublebase said:

-20 through -25 is what I was experiencing on my 2018 with 45,000 absolutely babied and well maintained miles.

I never knew if it was "normal" or not - only reason I even took a look is because of a cylinder number 5 misfire - which I never pinned down a reason for...random misfire, everything seemed ok. However I'd experience a misfire/shudder event when climbing a hill at highway speeds. I ended up trading it in at 50,000 miles - I think what finally did me in was the reports of fuel injector issues - that, and knowing that they were no longer covered under warranty. And I didn't like the fact that I had purchased a new truck and it couldn't make it up an incline on a highway without stuttering. Problem started at around 37,000 miles.

also pulled the pan on the transmission, thinking it was a tranny/torque converter issue, but everything looked good in there...no metal, nothing. Changed filter and fluid, no improvement.

I hear you, I cringe every time I see decent upwards incline. I can't complain about downhill though, does pretty good. lol