I have a 2006.5 Kia Optima EX with a 2.7L V6. I have 3 codes P340, P341 and P346 coming on.

EMS3716

MEMBER
2006 KIA OPTIMA
108,500 MILES

It is misfiring at 1500 rpms while under a load and I can feel it surging while stopped at a stop light. Sitting still in neutral is idles great and while driving at all other rpms it runs perfect. It started with just code P340 so we installed a new camshaft so we installed a new camshaft sensor on bank 1, and also went ahead and replaced the spark plugs, a new timing belt, and serpentine belt. Since then it has gotten worse. I have inspected all the vacum lines and connection and they look fine. I am clueless.

1 Reply

MERLIN2021

MECHANIC
17,250 POSTS

There was an ECM upgrade(replacement) did you have that done yet? Also this:
VPOWERTRAIN GROUNDS
TECHNICAL SERVICE BULLETIN
Reference Number(s): KT2009083101, Date of Issue: June 01, 2009
Related Ref Number(s): KT2009083101
ARTICLE BEGINNING
DESCRIPTION
Upon encountering powertrain DTC's, check that the powertrain main ground is good before
attempting any repairs.
When diagnosing any "P" or "C" Diagnostic Trouble Code (DTC) in which normal diagnostic steps
do not quickly reveal the problem, check that the powertrain assembly is properly grounded to the
body/chassis/battery.
Powertrain assemblies all have at least one ground to body/chassis/battery and in some cases more. A
poorly grounded powertrain assembly does not necessarily produce a "string" of DTC's; check the
connections even if you only retrieve one or two DTC's. Not identifying the poor ground can (and
does!) Lead to many hours being spent and parts being replaced unnecessarily.
Be aware that a quick voltage drop check between the powertrain and body/chassis/battery while at
engine idle or in the shop under low load conditions may not reveal this concern. Powertrain ground
requirements increase linearly (and substantially) with higher RPM/load conditions. It may be
necessary to drive the vehicle under similar RPM/load conditions as when the code set while taking
voltage drop recordings with a "min/max" capable digital volt meter.
Any indications of a poorly grounded powertrain assembly should be investigated and corrected prior
to performing any further in-depth repairs.

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