Will too rich melt the cat,or too lean? - Cars & Trucks

What code is it giving ? p0172 system too rich bank 1 ? If it is staying around 0.8 millivolts try introducing a vacuum leak an see if it goes lean ! If it does it is working fine . You probably have leaking fuel injectors or a fault fuel pressure regulator ! You need a better scan tool to check fuel trims , short term am long term ,to see if the computer is adding or subtracting fuel ! Oxygen Sensor Test fixed rich signal Ford O2 Sensor Testing

no. (but the isc valves loves to stick but will not cause black smoke)
the 4.0L is one of 5 million made, it's well known,
the black smoke don't lie. it's rich and the cat seems burned up too.
as with black smoke the cat will try to catalyze all that and glow red hot. is your cat missing?>
so why not believe the code 171, its real and is catastrophic failure. there are 2 engines here, FED and California.(exhaust)
(2 different exhausts and sensors there.
as they say, fix what is OBVIOUSLY bad, 171
(find why using tools or inspections)
Fuel System Lean (Bank 1)in most cases the exhaust is cracked near B1S1 0xy sensor
this causes it to stick at 0volts, (lies) and the PCM sees that obvious lie then goes rich. (limphome rich)
if the pcm cant measure oxygen, it must now guess at fuel trim.(bad that.)
it goes rich, so you dont melt pistons running lean.
(by design)

bad front oxygen sensor (aka , up stream bank 1)
in calif cars, it can have a split exhaust on the I6 and have 3 sensors. (hope not yours, do look..)
most have 2 sensor, front and the useless behind cat sensor(B1s2)
S2 is useless for running mix, the rear is for smog test the cat.

so it rich, and now misfires. and the spark tips are black.
and it misfires to bad it can even idle, sure. (Drops)
the cause, is too rich.
the 171 means the PCM sees it stuck at 0v forEVER.

there are in fact other causes.
but these 2 are top cause.

on all 3 of my 4.0L engines
the exhaust manifold cracked on the under side.
side facing block. (i use a hose to ear to hear the putt putt puts, (with FULL PPE protection from burns from a dead cold engine.) ask how.
even the SST exh. man. did that.

or the header flange gasket is TOAST. (that too putts when bad.)

too rich causes overheat

yes it can the o2 sending unit talks to the cars computer saying if the fuel is to rich or lean you may have more than one on the exhaust

There has to be codes. Well you melted another converter. Your injectors are leaking and the raw gas is overheating and melting your converter Your plugs are black that means way over rich and no codes? If you take the cat loose it puts a code in immediately

high NOX indicates your engine is running high combustion temps. Two of the major reasons for lean mixtures are intake leaks and clogged fuel injectors. The reason the engine computer cycles between rich/lean when running is because the cat needs lean mixtures to deal with HC and CO and a rich mixture to deal with NOX. If you are running lean the cat can't lower your NOX. I would first get your fuel injectors flushed and de-carbonize your intake/combustion chambers.

Hi,

The front O2 sensor is what the ECU uses to determine the correct air/fuel mixture to keep the engine running correctly, the rear sensor is purely to measure catalyst efficiency. Once the car has warmed up and the sensors are in what is called `closed loop` this means the engine is no longer in the warm up stage and the catalyst is hot enough to be working efficiency you should expect to see the front sensor constantly changing between rich and lean when idling or cruising at approx 2500 to 3500 rpm, the rear sensor should be more or less constantly reading lean. If you find that the rear sensor is mimicking the front sensor i.e. constantly switching rich to lean then it indicates your cat is not doing anything and you most probably have a defective cat.

Be sure before changing the cat to check for anything on your engine that could be causing a problem, air leaks on the inlet or exhaust system will cause the front sensor to read lean and the engine ecu to try and compensate by richening the mixture, this may artificially correct the reading from the front sensor but will cause the rear sensor to pick up a rich reading, similarly a slight misfire will cause unburnt fuel to enter the exhaust giving a rich mixture reading from the front sensor and will also burn the cat out very quickly.

Hope this helps and good luck, thanks for using fixya

John

It isn't a restriction. Cat's glow red when the engine is really lean or the timing is wrong.

I don't see that happening because exhaust gases are forced away from the engine and that would cause the converter pieces to flow out of the tail pipe not only that but catalytic converters don't get problems from engine running lean it happens from running rich causing excess fuel to burn in the converter and melt it

those codes are for lean engine condition look for vac leaks at the back of engine to the pcv valve could hear hissing noise with engine running also check egr valve to be stuck open also when was last fuel filter changed? hope this helps .