Possible Solution to P0420 Code

[99svtc]

Well...You were right BrApple, I did get a CEL on again... This Time I have 0174 and 0171... Doing some research and saw a reply from you:

[FONT=arial,verdana,helvetica,sans-serif]P0171 - [/FONT][FONT=arial,verdana,helvetica,sans-serif]System Too Lean - Bank No. 1. [/FONT]

[FONT=arial,verdana,helvetica,sans-serif]P0174 - [/FONT][FONT=arial,verdana,helvetica,sans-serif]System Too Lean - Bank No. 2.


Already replaced UIM and LIM. Guess that leave 02, or fuel pump/fuel filter?

EDIT:
Also found this, maybe leaking at the gaskets I just put on?
[/FONT]Fuel System:
· Contaminated fuel injectors
· Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions)
· Vapor recovery system (VMV)
Induction System:
· MAF contamination
· Air leaks between the MAF and throttle body
· Vacuum leaks
· PCV system concern
· Improperly seated engine oil dipstick
EGR System:
· Leaking gasket
· Stuck EGR valve
· Leaking diaphragm or EVR
Base Engine:
· Exhaust leaks before or near the HO2S
· Secondary air concern
Powertrain Control System:
· PCM concern

 

[BrApple]

you can check the fuel pressure if you want, can't hurt. bet you haven't changed the fuel filter in some time anyway.

as for the codes, recheck the work you just did. however most of the time with both of those codes its often related to the maf if there are no vacuum leaks. try cleaning the maf after checking for vacuum leaks and go from there.

 

[greasemonkey1489]

Cleaned my stuff today...

Cleaned my stuff today...

AND BOY, WHAT A DIFFERENCE! The throttle response is great and there is 0 hesitation down low. The transition when the secondaries open is incredibly smoooth

BEFORE:

Power washed in a spray cabinet with a water-soluble solvent. Cleaned up nicely :drool:

AFTER:

 

[99svtc]

you can check the fuel pressure if you want, can't hurt. bet you haven't changed the fuel filter in some time anyway.

as for the codes, recheck the work you just did. however most of the time with both of those codes its often related to the maf if there are no vacuum leaks. try cleaning the maf after checking for vacuum leaks and go from there.

Replaced the Fuel Filter and Cleaned the MAF last August. I'll recheck my work and check for leaks.

Main symptom is when coming up to a stop, the RPM will drop to 500(sometimes a hair lower), and then shoot itself back up to normal idle.

Thanks again

 

[99svtc]

AND BOY, WHAT A DIFFERENCE! The throttle response is great and there is 0 hesitation down low. The transition when the secondaries open is incredibly smoooth

Looks like a nice clean job!

 

[beyondloadedSE]

Back to the EGR passages.. if the passages are clogged, then the engine cannot cycle exhaust gases back through the engine to "dilute" the fuel/air charge causing a slightly "rich" condition. EGR systems are to reduce emissions and increase fuel economy, especially at cruising speeds (>45mph). SO, if the fumes are too rich, the downstream o2's sample the fumes and the voltage reading indicates a "low efficiency" after the catalyst, you get a lovely, orange CEL.

My first thought was if the EGR passage was clogged, it would cause the exact opposite, a lean condition. The EGR is recycling unburned fuel, thus adding more fuel. I don't understand how taking the EGR away would create a rich condition.

 

[striker2]

My first thought was if the EGR passage was clogged, it would cause the exact opposite, a lean condition. The EGR is recycling unburned fuel, thus adding more fuel. I don't understand how taking the EGR away would create a rich condition.

actually, the EGR has no effect on the actual A/F ratio. EGR gases are inert. if the EGR is open, the engine will be pulling less air through the MAF and thus the PCM will give it less fuel so the ratio is still correct. EGR simply dilutes the mixture so there is less of it in the combustion chambers, which lowers combustion temps. lower combustion temps lower NOx emissions, thats all the EGR is used for and its only used during cruise/light throttle conditions.

blocked EGR passages will have no effect on the A/F ratio and as such will not effect the efficiency of the CATs.

 

[greasemonkey1489]

My first thought was if the EGR passage was clogged, it would cause the exact opposite, a lean condition. The EGR is recycling unburned fuel, thus adding more fuel. I don't understand how taking the EGR away would create a rich condition.

...Uh, unburned fuel? How does it select that? Whatever is in the exhaust manifold is whatever is cycled through the engine.

Either way, I don't think this is coincidental. After that cleaning and work, no more code and the engine runs very, very strong.

Yes, I know that the EGR is meant to lower emissions but think about it. If the EGR dilutes the mixture in the combustion chambers, the exhaust will come out with lower NOx emissions than if the EGR wasnt present. Then the post-cat O2 would read higher than normal tripping the CEL.