This may never happen to anyone, but it's an interesting bit of diagnostic sleuthing.
I took my GT to my GT tech after repeated CEL and P0174 codes. This code indicates a lean condition in bank 2 (driver side). When the PCM detects the lean condition, the response is to go full rich. Too rich is not good, but too lean can be really bad. Full rich is a safety measure. The engine ran fine, but eventually the plugs would foul.
My GT has a pulley and tune, Accufab TB, and FRPP/Borla long tube headers and muffler.
Diagnostic steps:
- Verify no vacuum leaks with smoke generator
- Verify correct flow from fuel injectors
- Verify operation of O2 and MAF sensors
- Verify compression and leak down
- Test circuits from PCM to Bank 2 O2 sensor 1
- Perform visual inspection of exhaust valve springs
At this point, it's important to note the difference between OEM exhaust manifolds and long tube headers.
The OEM setup has O2 sensor 1 sampling the oxygen content of all four cylinders in the bank.
The long tube header has O2 sensor 1 sampling only cylinder 7 (see bung location in the image).
This means that cylinders 5, 6 and 8 could be too lean or too rich and that condition would not be detected!
So, what could be wrong with cylinder 7 to cause an apparent lean condition?
At this point, the tech swapped and rewired the O2 sensors to sample from cylinder 8. Sensor voltage and A/F mixture returned to normal! (He demonstrated this to me and Howard on his laptop...pretty cool).
Next, he put some rubber gloves over the exhaust outlet tips and blew smoke into the exhaust system. Smoke leaked from the slip-fit header connection, which is adjacent to O2 sensor 1.
The tech determined that the header was drawing enough external air at the slip-fit connection to fool the O2 sensor in the cylinder 7 tube into a "too lean" reading. The O2 sensor in the cylinder 8 tube is well downstream of the slip-fit connection (see image) and is not affected by the leak.
At this point, the rewired O2 sensor may be the final solution. We're seeing if Borla will supply a bank 2 header under warranty.
An unusual problem to say the least.
One takeaway for anyone with headers is don't count on the PCM to let you know if you have a lean condition on six of the eight cylinders. This should be obvious if you look at the O2 sensor locations, but I never thought anything of it.
Very happy to have the GT back in the garage!
I took my GT to my GT tech after repeated CEL and P0174 codes. This code indicates a lean condition in bank 2 (driver side). When the PCM detects the lean condition, the response is to go full rich. Too rich is not good, but too lean can be really bad. Full rich is a safety measure. The engine ran fine, but eventually the plugs would foul.
My GT has a pulley and tune, Accufab TB, and FRPP/Borla long tube headers and muffler.
Diagnostic steps:
- Verify no vacuum leaks with smoke generator
- Verify correct flow from fuel injectors
- Verify operation of O2 and MAF sensors
- Verify compression and leak down
- Test circuits from PCM to Bank 2 O2 sensor 1
- Perform visual inspection of exhaust valve springs
At this point, it's important to note the difference between OEM exhaust manifolds and long tube headers.
The OEM setup has O2 sensor 1 sampling the oxygen content of all four cylinders in the bank.
The long tube header has O2 sensor 1 sampling only cylinder 7 (see bung location in the image).
This means that cylinders 5, 6 and 8 could be too lean or too rich and that condition would not be detected!
So, what could be wrong with cylinder 7 to cause an apparent lean condition?
At this point, the tech swapped and rewired the O2 sensors to sample from cylinder 8. Sensor voltage and A/F mixture returned to normal! (He demonstrated this to me and Howard on his laptop...pretty cool).
Next, he put some rubber gloves over the exhaust outlet tips and blew smoke into the exhaust system. Smoke leaked from the slip-fit header connection, which is adjacent to O2 sensor 1.
The tech determined that the header was drawing enough external air at the slip-fit connection to fool the O2 sensor in the cylinder 7 tube into a "too lean" reading. The O2 sensor in the cylinder 8 tube is well downstream of the slip-fit connection (see image) and is not affected by the leak.
At this point, the rewired O2 sensor may be the final solution. We're seeing if Borla will supply a bank 2 header under warranty.
An unusual problem to say the least.
One takeaway for anyone with headers is don't count on the PCM to let you know if you have a lean condition on six of the eight cylinders. This should be obvious if you look at the O2 sensor locations, but I never thought anything of it.
Very happy to have the GT back in the garage!
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