1996 Emission Issues – P0420

[stan the man]

I installed the Bassani headers, y-pipe, and Auto Zone tailpipe several years ago. Everything has worked great however, every winter I pop off a P0420 emissions code (Bank 1).

Does anyone know why this happens only in the winter time or how to fix this? I have to smog my truck in the next couple of weeks and want to fix the issue more than dumb luck.


Here is some information pulled from the Freeze Frame:
P0420
Bank 1

Fuel Sys 1 – CL
Fuel Sys 2 – CL-Fault
Calc Load (%) – 65.10
ECT (ºF) – 185
STFT B1 (%) – -3.13
LTFT B1 (%) – -2.34
STFT B2 (%) – -3.91
LTFT B2 (%) – -2.34
Engine – 1883
Vehicle Speed (MPH) – 53

[omp]

Have you checked for leaks? I had lots of leaks by collector and gasket was popping code on bank 1 as well. Snugged up bolts have not seen it for 250 miles.

[stan the man]

Originally Posted by omp

Have you checked for leaks? I had lots of leaks by collector and gasket was popping code on bank 1 as well. Snugged up bolts have not seen it for 250 miles.

Simple enough. I can try that as a starting point. I will let you know what happens in the next few days.

[miesk5]

yo Stan;
This is by Ford in a 96
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Indicates Bank 1 catalyst system efficiency is below the acceptable threshold Use of leaded fuel
Damaged HO2S
Malfunctioning ECT
High fuel pressure
Damaged exhaust manifold
Damaged catalytic converter
Oil contamination
Cylinder misfiring
Downstream HO2S wires improperly connected
Damaged exhaust system pipe
Damaged muffler/tailpipe assembly
Retarded spark timing
Compare HO2S upstream & downstream switch rate. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S quite slow compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly approaching the switching rate of the upstream HO2S. Once beyond an acceptable limit the DTC is set.

[cajunrebel]

How far from the manifolds are your O2 sensors? If they are too far away you may not be keeping them warm enough when its cold outside. If so wrapping the exhaust or moving the sensor closer to the manifold will help.

[TheUnforgiven]

those rear o2 sensors need to be in the stock location related to the cats.

[96EB5.8]

Unless you find a leak in the exhaust you need a new catlyst. I have seen this many times on all different vehicles and it almost always comes down to the cat.

[cajunrebel]

Looking back at your freeze frame data, your truck was popping the code at 1883 RPM and 53 MPH, unless that was right after you hat taken off moving your O2 sensor should have been warm. Most of the time when the sensors don't stay warm enough it is when you are sitting still idling for some time. You make no mention of if you installed new cats or not. If they are original they could be failing.