QuestionMy van misfires at 40-55mph. The plugs, wires, coil, and serpentine belt, and EGR valve was changed in August 2008. Changed the front 3 plugs and wires again today. It still misfired so I took it to an autoparts store to get the codes read and it came back as: random misfire, misfire on cylinder 2, and misfire on cylinder 5. What is my next step? The van has 170,000 miles with the original motor.
AnswerHi Charlie,
An examination of the ignition patterns with a scope is recommended, but since you don't have one then the other possibilities are:
check the fuel pump pressure (there is a test port on the fuel rail on the side of the engine adjacent to the oil filler cap, spec is 49 psi: if low begin by changing fuel filter);
second, assess the possibility of engine mechanical problems by means of a vacuum gauge reading of the intake manifold vacuum pattern (I can xerox copy and postal mail you a page that shows how to interpret such patterns).
It is also possible that the injectors could be in need of cleaning, or again at a shop with the aid of a diagnostic control tool the injectors can be individually "killed" to sense for if the injectors on particular cylinders are the problem.
The earlier maintenance you performed has already covered the other possible causes as shown in the shop manual.
Roland
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