P0171 and 30% LTFT
Thread Starter
Heel & Toe
Joined: Dec 2024
Posts: 23
Likes: 11
P0171 and 30% LTFT after replacing all injectors
Model: 2015 C7 Z06 A8
Mileage: 30,000 miles
Mod: Corsa intake, NPP fuse pulled, no additional tunes or modifications.
Note: There is no official Chevy/GM service center in my country.
It was difficult to start (requiring 5–8 seconds to crank), exhibited rattling, and had fluctuating RPMs (+/- 200 RPM) after starting.(Becomes stable after engine is warmed up)
Occasionally, the engine RPM would hang at around 1,000 RPM when I took my foot off throttle.
After diagnostics at a local auto shop, it was determined that several injectors needed replacement.
The shop replaced all injectors with brand-new GM high-flow injectors (Part No. 12668397).
The Long-Term Fuel Trim (LTFT) for Bank 1 is abnormally high at 30%.
We couldn’t find any similar cases since there are very few C7s in our country.
We reached out to several owners and auto shops that have experience servicing C7s,
but none of them have encountered the same issue.
Any insights or advice would be greatly appreciated.
Mileage: 30,000 miles
Mod: Corsa intake, NPP fuse pulled, no additional tunes or modifications.
Note: There is no official Chevy/GM service center in my country.
Actions Taken:
- Replaced all injectors due to multiple cylinder misfires and engine light.
- Tested for vacuum leaks using a smoke machine—no leaks were detected.
- Checked the high-flow air sensor, which is functioning properly.
Description:
This car experienced multiple cylinder misfires, triggering codes "P0300" and "P050D."It was difficult to start (requiring 5–8 seconds to crank), exhibited rattling, and had fluctuating RPMs (+/- 200 RPM) after starting.(Becomes stable after engine is warmed up)
Occasionally, the engine RPM would hang at around 1,000 RPM when I took my foot off throttle.
After diagnostics at a local auto shop, it was determined that several injectors needed replacement.
The shop replaced all injectors with brand-new GM high-flow injectors (Part No. 12668397).
Current Issue:
The original codes "P0300" and "P050D" are now resolved, but a new code, "P0171" (Bank 1 lean), has appeared.The Long-Term Fuel Trim (LTFT) for Bank 1 is abnormally high at 30%.
- Multiple smoke tests were conducted to detect vacuum leaks, but none were found.
- The engine sounds like it is struggling to breathe immediately after starting.(Becomes stable after 10~20 sec.)
- If the throttle is opened during this time, the engine stalls.
- After clearing the "P0171" code and performing a test drive, the code reappears immediately.
Question:
Could the shop have missed any inspection steps or made an error during repairs?We couldn’t find any similar cases since there are very few C7s in our country.
We reached out to several owners and auto shops that have experience servicing C7s,
but none of them have encountered the same issue.
Any insights or advice would be greatly appreciated.
Last edited by yhsieh927; Dec 20, 2024 at 03:53 AM.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,621
Likes: 4,066
From: Cape Coral, Florida
What are the LTFT’s for bank 2 ??…it may be close to setting a P0174 so if we have 1 bank lean or both requires a different diagnostic approach…you are either turning right or left in the diagnosis…if the long terms decrease at 3000 RPM after a bit you have a vacuum leak…if long terms remain high under load with long terms elevated on BOTH banks it’s either a fuel delivery or MAF issue…the MAF reading at hot idle should be at the liter displacement of the engine in grams/second.
Instructor
Joined: Apr 2014
Posts: 136
Likes: 15
From: TN
P0300
Did you check both low side and high side fuel pressures prior to replacing anything fuel system? Also, individual injector resistance, operating vdc and injector pulse to injectors suspected? I believe that unless fuel contamination was at play, multiple injector failures are not your problem. I'd check those fuel pressures to start with.
