There are a few reasons your Ford F-150 could have failed NO. The most
common is the malfunctioning EGR system. Your Ford's EGR valve is
responsible for re-circulating a small amount of exhaust gas back into the
combustion chamber. This is done to cool down the chamber temperature by
producing an inert gas along with the regular fuel mixture. Nitrous Oxides
emissions are formed when engine chamber temperatures rise above 2500* F.
Keeping the chamber cool reduces NOx emission.
The EGR valve on your Ford should be inspected to ensure its proper
operation. A working valve should be able to open its passage using manifold
vacuum. Manifold vacuum is created during the engine's intake cycle. The
high demand for air during this cycle creates a vacuum within the engine's
intake manifold.
The EGR system is prone to collecting carbon build-up. Since the EGR valve
pulls exhaust gasses from your exhaust and introduces them back into your
engine's intake air over time it will become clogged or stuck open/closed
from the carbon deposits. It is possible to clean the EGR valve if you
remove it from your vehicle and either spray it out or let it sit in regular
gasoline.
Lean Fuel Mixtures - Lean fuel mixtures cause high NOx also. If your Ford
F-150 is running lean (indicated by low CO emissions) high NO would result.
A lean fuel mixture is when the engine receives less fuel then is necessary
to obtain efficient combustion. Lean fuel mixtures are often due to vacuum
leaks. These leaks will allow the suction of additional and un-metered air
into the combustion mixture or exhaust (depending on where the vacuum leak
is located) disturbing pre/post fuel combustion and increasing NOx
emissions. Vacuum leaks are often hard to diagnose as they may be present at
locations not easily viewed.
We have to recommend you have a smog check repair station first inspect your
Ford's EGR system, and then ensure the fuel feedback system is functioning
properly.
