Justice10

So lately I'm getting these 2 codes P0172 "System too Rich Bank 1" and P0420 "Catalyst system efficiency below threshold bank 1."

I've been doing some research, and it says the main focus for those are MAF Sensor which i replace last week with the air filter because they were really dirty. Then I search around the under the hood to see if there were any vacuum leaks and there wasn't any. But then still got those 2 codes again.

Then I did more digging, and I came across a video and a post with someone has the same problem and their solution was replacing the intake manifold because it was a leak on its left side.

So, I turn on the car and went to check on the intake manifold to hear air following through. The thing is that it was loud, so I couldn't figure out if it was an air leak or that its normal sound of sucking air. I checked for vacuum suction with my fingers, I checked the back hose on the left back side to see if it was loose and also check the control arm on the left side as well. Either way, I came up with nothing? Don't know what else to look for. Is there something that I miss?

Mesquite77

For a rich code like P0172, I wouldn't be looking for manifold leaks, that would make it lean.

Replacing the rear bank 1 O2 sensor (the easy one to get too), may cure the P0420 and by proxy the P0172. It is easiest thing to try. Pulling the plugs and doing compression check, inspecting injectors, coil and plug checks on bank 1 are a lot harder, and I would try all that before replacing the cat...

Long and short fuel trims would be interesting to see if things change when transitioning from open to closed loop operation. I.e. is the O2 sensor behaving normally, etc.

Justice10

So i did what you said i checked the spark plugs, coils, and fuel injectors. Then replacement with the ones in front of the engine because they were newly replaced with in week. Now I'm getting P0175 which is "Fuel Mixture imbalance". When I made sure that I put everything back perfect. So what now?

Margate330

The fuel trims chamge depending on the fuel map, load, and rpm.

For the fuel trim and MAF numbers to be meaningful please post them up, engine warmed up and at idle, car in Park, accessories and AC off.

At idle gives us a baseline.

Ps- MAF affects both banks equally so it won't help for diagnosing a single bank issue.

Mesquite77

Looks like now bank 2, the radiator side, is running rich, way rich. This will be due to poor combustion in one or more of cylinders 2,4 and or 6. Compression, spark, fuel and the A/F (not O2) sensor on bank 2 are suspects. Are the plugs "wet" on one of these? Is each getting spark? Wonder if a fuel injector is stuck open?

>>>> Then replacement with the ones in front of the engine because they were newly replaced with in week

Do I read your post as if you put plugs from bank 2 (radiator side) into bank 1 (firewall side), and now the old plugs from bank 1 are now in bank 2? If so, then I would suspect those plugs.

Justice10

Yes I move those spark plugs, coils and fuel injectors to the front because it's easier to change out other than having to move all those stuff just to get to the back. Also the ones that used to be in front is brand new so I don't have to worry about it being faulty anything soon.

Justice10

Ok so this is what i got. I had to wait for the next day to do so because i was busy running up and down the whole day yesterday.

Idle car: 20 mins:
Short fuel trim bank 1: 0.78-1.56% (Keeps jumping in that range)
Long fuel trim bank 1: -17.19%
Short Fuel trim bank 2: -8.59 - -10.94%
Long fuel trim bank 2: -32.03%
MAF Entry flow rate: 3.50- 3.71g/s

Idle car 40 mins:
Short fuel trim bank 1: 0.78-1.56% (Same as before)
Long fuel trim bank 1: -12.50% (Change)
Short Fuel trim bank 2: -1.56 - -3.91% (Change)
Long fuel trim bank 2: -32.03% (Same as before)
MAF Entry flow rate: 3.50- 3.71g/s (Same as before)