While driving it just started to miss a little then got worse. Service
engine light started blinking. Made it home OK but it's not drivable
now. You could nurse it along for a few blocks but it shudders and pops.
New one for me. Bad gas? Fuel filter? Any help greatly appreciated.
The "computer" will only identify the cylinder(s) that are not firing, either
through a misfire code or a power balance test. Once the "bad" cylinder(s) is
identified, you will have to check for compression, spark, and fuel supply to
If the miss started suddenly, the problem is likely a dead spark plug, a dead
or a dead injector. Another possibility, if the miss developed over a period
time, is a spark plug wire arcing through the spark plug boot.
You can identify the missing cylinder by unplugging the electrical connector on
injectors one by one with the engine running. You will notice an RPM drop or a
worsening miss. If you find one that makes no difference, that's your dead
Pull your spark plug wires off of the spark plugs and check for oil on the
for signs of arcing, usually grey spots and pinholes on the side of the boots or
pencil like lines out of the boot opening. If there is oil on the boots, the
cover seals are leaking and will need replaced along with the wires.
Remove the spark plugs and look at them. The plug in the dead cylinder may
either cleaner or dirtier than the rest. You can rule out the spark plugs by
replacement, they are inexpensive and probably needed anyway. About $16 max.
You can test for spark at each wire with an inexpensive Spark Tester. It looks
a spark plug with a clip on the side. No spark points to a dead coil pack. (This
usually cause a miss on 2 cylinders).
If the plug wire and spark plug on the "bad" cylinder are ok, and there is
present, you likely have a dead injector.
The above steps should locate your miss. Low compression will cause a miss,
is uncommon. If you have access to a compression tester and know how to use it,
can't hurt to check. Another possibility is a PCM not triggering a section of a
or an injector, again this is not common.
Hope this helps, Tom
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