I just added the Dynatech Long tubes with high-flow cats (with SLP catback) I am getting the P0420 Low Efficency bank code, which from what I understand is being caused by my stock O2's not liking the Highflow cats...I have no other codes. Car seems to run great.
am I loosing any performance by running with this code?
LS1 edit can't really help with this code right? I either have to get 02 sims or Wideband 02,,,is this correct?
I just don't want to hurt the engine or loose any performance. The check engine light and this code only come up occasionaly.

sorry for the basic question, I am still a newbie in the "tech" sense of a vette

 

What I have heard about some metallic high flow cats is that you need to have the code blocked out with LS Edit or other software. Closed loop control should still be working once the engine heats up to 150 F. (Up stream O2's controls the A/F ratio). You should not need wideband unless you want a A/F ratio guage.

 

I had the same issue a few months after installing my SuperMaXX's. This is a common issue on cars with longtubes and highflow cats. You can disable the code with LS1 Edit, HP Tuners, or EFI Live.

Set DTC 420 and 430 to 'no error reported' and you won't get the MIL.

Good Luck!

 

Just installed the Dynatech Supermaxx with high flow cats, x-pipe and Corsa Indy cat back. I'm getting the same codes. Guess it time to block them.

 

P0420 means that the rear O2 sensor is having the same amount of voltage swing as the front O2... whick means simply means the cat is not doing it's job. High flow or not, it's a bad cat

-devettetech

 

If the exhaust and cats were stock I would agree, but with longtubes the sensors are much further back than stock. The mounting location of the sensors does affect the tune and sensor calibration.

If the cats were bad, than the code would be persistant but it's not. Mine would only come on after long periods of idleing or after coasting down to a stop from a long drive on the highway on a wet or humid day. From what I can tell without a scope and only a scanner, it seems like its related to the lack of heat in the exhaust at the B1S2 and B2S2 sensor locations. My rear sensors pass the R-L and L-R swing time tests with flying colors and don't consistently hold the same oscillation pattern when idleing. They oscillate fine when driving. I bet there is a table in the PCM that controls this but we don't have access to it.

Have you scoped the rear sensors on a Vette with longtube headers?

 

That is not really right i am afraid. Although having the cat further back can extend the time it takes to get to operating temp, the O2 sensors do not require calibration.

The only way to really diagnose this problem is to use a Labscope, as you said, or use a high speed data link and graph O2 response of the rear O2's at a steady state cruising speed. I have seen many high flow cats work just fine, and others... not so good

 

I agree that the O2 sensor doesn't require a calibration, but the PCM has a software arguement that has to be satisfied before the code is indicated. This arguement is controlled by a table or a value just like the B1S1 and B2S1 switch points, etc.

Moving the O2 sensor's down stream does affect their output to the PCM, which I can surmise is from the lack of heat at the sensor.

Do you have access to any graphs that illustrate the rear O2 sensor outputs on a Corvette with longtube headers? I haven't seen a Corvette with longtube headers and highflow cats that didn't show these codes; which would mean that all Corvette's with longtube headers and highflow cats have defective cats.

 

I have not saved any charts lately but I will get one and post it here ASAP.

The rear O2's are heated so they come online fairly quickly, so heat for the O2's really isn't the issue... but heat would be an issue for the smaller cats mounted too far back from the collectors.

The following is an excerpt straight from GM catalyst diagnostics, "A good catalyst (e.g., 95% hydrocarbon conversion efficiency) will show a relatively flat output voltage on the post-catalyst HO2S. A bad catalyst will show peaks and valleys in output voltage. This indicates that the catalyst has lost some of its ability to process the exhaust gases properly. A catalyst that indicates a reduced efficiency based on the post HO2S is likely to be inefficient at converting not only HC, but CO and NOx as well. The post-catalyst HO2S is used to measure the oxygen storage/release capacity of the catalyst. From this we can infer the oxygen storage capacity of the catalyst. A high oxygen storage capacity indicates a good catalyst. A low oxygen storage capacity indicates a catalyst that is failing. The TWC and oxygen sensors must be at operating temperature to achieve accurate oxygen sensor voltages."

The above clearly identifies that rear O2 voltage movement, greater than expected for that driving condition, is the sole factor in catalyst efficiency tests. The cat could still allow the vhicle to pass tailpipe tests, but the rear O2 sensor would set a code in order to have the catalyst system evaluated.

It is also safe and fair to say that I have seen primary O2's that are sluggish (transitions from lean to rich / rich to lean) can case poor fuel control and thus mimic a faulty convertor