Like the title says, can a bad catalytic converter cause a lean condition (p0171)? I was a tech for years at honda and never saw a lean condition/code that was causes by a blocked catalytic converter. I've seen lean conditions lead to a bad cat but never vise versa. Thanks ahead of time.

 

P0171 ? Fuel trim (FT) system too lean, bank 1 ? OBD2 Trouble Codes

 

​​​​​​​Thanks tamboo, I apreciate the link but I'm looking more for personal experience with this purticular issue. I see half the sights online are listing the cat as a possible cause of a lean condition while the other half dont even mention it.

 

Probably not, the O2 sensor for the fuel trim is located before the cat. The sensor after the cat is only to determine if the cat is bad (P0420). If the cat is completely clogged so that it wont flow, it would be rich, not lean (more fuel than airflow).

 

​​​​​​​ Thats what I'm thinking but my friends that still work at honda are convinced the cat and my front o2 sensor not being a honda oem sensor are causing all my problems (p0171 lean condition,slightly low rough idle, car wont rev past 6500-7000 rpm). I've already went through a smoke test, fuel pressure test, new injectors, 2 new direct fit ngk and bosh front o2 sensors and a an ecu. I just dont know what to do at this point. I'm getting the p0171 code and every now and then a p0420 but I beleive that code is only being thrown because of the lean condition.

 

try a denso o2 sensor?
with just about everyone moving manufacturing to china
most parts are now hit or miss.
this includes big names like brembo and gates.
bosch has been a gamble for decades- avoid like the plague.
just had a gates water pump bite it after only 5 years.
bought npw this time for made in japan goodness.

 

I actually have a denso on it now lol. I tried a bosch and ngk before the denso and was getting a p0133 code along with the p0171 until I switched to the denso. I also had a problem with the gates blue racing belt on my 04 sti I just sold. The belt was slightly to small and was whining while The car was running ,sounded like a supercharger and the tensioner was fine so it wasn't the tensioners fault. So my friends are telling me if the cat is partially clogged it could be causing some back pressure and pooling up air by the o2 sensor. The o2 sensor thinks its getting to much air and adds more fuel. Problem is my spark plugs are a little white so I dont think its a false reading. I'm either getting to much air in the combustion chamber or not enough fuel. Problem is my fuel pressure test was like 52 psi and when I would rev the car up it was sky rocketing to the 70s or 80s. My vacuum pressure is -21inhg and it only fluctuates -/+.5 inhg which I belive its only doing because of the slight miss at idle from the lean condition. Maybe my throttlebody or intakemanifold is leaking? I did a smoke test and didnt find anything, I also sprayed carb cleaner around the intake manifold, TB and all vacuum lines and found nothing. The prevouse owner is trying to tell me its the fpr but my fuel pressure is to good for it to be a fuel flow problem and although the injectors made my car idle a little smoother theres still an issue there. I have a slight leak on the b pipe were the pipe meets the catalytic converter. It's pretty close to the front o2 sensor but its still downstream of it so Idk. Should I take the plunge and try a honda oem o2 sensor or should I just buy another denso?
​​​​​​​ Thanks for the help tamboo.

​​​​

 

says here that denso and ngk make the honda part:

https://honda-tech.com/forums/honda-...civic-3114911/

kind of an old thread but not sure who else would be making them.
tried the propane trick?

Understanding Oxygen Sensors to Diagnose Fault Codes

 

For this article topic, I registered this forum account
Sorry for my poor English, all translated by Google.

I'm testing an E46 330i M54.
Bank 1&2 LTFT is +12%
Bank 2 catalyst is blocked (some melt damage on the surface)

I have a theory in this case, but I haven't fixed the problem yet.
The catalyst is blocked and the MAF value decreases.
This results in less fuel and a lean A/F.
Then the fuel trim goes higher.

If the ECU only has MAP (like EJ or EG without MAF), there may be exhaust backflow and low intake manifold vacuum.
I guess it will run rich.

So maybe LEAN or RICH both may happen.
The above cases and conjectures are for reference only.