Symptoms:

This 2002 F150 Ford Truck has a misfiring code on one bank. The engine is 4.2L and had a tune up about a week ago. It has lots of misfiring codes on bank 1 accompanied by severe hesitation.

Diagnostics for 2002 f150 Ford Truck with Code:

When scanned for codes it showed P0301, P0302 and P0303 on on bank 1. When the spark plugs were removed from cylinders 1,2 and 3; they were coated with carbon soot which showed it was running rich.

While the spark plugs were out, took compression readings and they all read above 130 psi. Cleaned the spark plugs and installed back. Took vacuum reading reading and it was normal at 20 inches of Hg. Tested the PCV valve, vacuum hose lines and intake manifold gaskets for vacuum leak and none were found. The egr system was checked also and it tested fine.

Checked both catalytic converters and the one for bank 1 looks damaged because bank 1 was running rich. Replaced Catalytic converter for bank 1 including the bank 1 post oxygen sensor. Still has a misfire on bank 1. Performed an injection balance test and it showed all injectors were OK.

Cleaned the mass sensor and took for a drive but still the same. Took the scanner fuel trim readings and it showed LTFT (long term fuel trim) bank 1 at -17% and LTFT bank 2 at + 16%. Took out the ignition coil pack and substitute one coil at a time with a new one. Misfiring stopped. Replaced all ignition coils with OEM parts and road tested the vehicle and the misfiring flashing code disappeared completely. Verified with the scanner and fuel trim showed LTFT at both bank 1 & 2 hovering between + and – 3%.

Notes for 2002 f150 Ford Truck with Code:

Before replacing all the above parts, the LTFT % readings must be measured first. The original culprit here seems to be a weak ignition coil causing the misfire in the first place. As a result, one bank of cylinders run rich which ultimately took out the catalytic converter.

Although this truck was just tune up a week ago, an electrical component can fail anytime. This explains why it was working fine last week during the tune up.

This 2002 F150 Ford Truck with code lessons are available in ATS database to help you save money in fixing your vehicles.

Thanks,

Richard