unplug the spark-plug: error code or not?

Hi,

To make sure all 4 cylinders are running, I unplugged the high voltage
wire from each spark plug (one a a time, not all at once). Each time
the idle RPM dropped a little bit, so I said "OK, each cylinder must be
firing properly".

However, I drove later to AutoZone and asked them to check the error
codes, and there were NONE! not a single error code. So why there were
no error codes? Also, with one wire unplugged, the Check Engine light
did not come on (the lamp is OK, it comes on at start-up).

All this is for a 97 Civic LX by the way.

Thanks

 

Why would there be any error codes in the first place? Were you
experiencing a misfire or something?

 

no, I wanted to *cause* an error code... if I pull the plug, the
cylinder does not fire, so it should generate an error code, I would
think

just trying to understand what the OBD-II does. thanks.

 

what problem are you trying to diagnose? plugs are so cheap, if you
have any doubts, just replace them.

regarding codes, fwiu, you /should/ get a code from a "misfire". it's
detected by registering a change in the angular velocity of the
crankshaft and should indicate /which/ plug is misfiring. but the ecu
may not trigger a misfire code below certain revs or maybe if it's not
misfiring for very long - just guessing because idle can give erratic
crank rotation speeds hence the need to not be too sensitive and plugs
self-clean when hot, hence the need to ignore any misfire when still
warming up...

if anyone knows for sure, please post.

 

If I remember correctly, the MIL will illuminate if the ECM determines that
the engine has exceeded Federal emissions limits by 150% on at least TWO
consecutive "drive cycles".

You'd need to pull the plug, let it misfire fifteen seconds or so, plug it
back in and drive the car to full-warm. Then shut it off and let it cool
completely (overnight is good), then repeat the whole thing the next day.

That ought to set the MIL. But 15 seconds misfire may not be enough (about
188 revs at 750rpm), and leaving the plug off for longer risks damaging
your coil.

 

good points Jim.

Regarding your question: I think the car is not as powerfuls as my
wife's car (i know, mileage, age, 1.6 vs 1.7 L engine), but still, I
think it's missing a few horses. So I wanted to make sure all 4
cylinders fire properly. I was just wondering why I didn't get error
codes.

Thanks.

 

replace plugs, leads, distributor cap & rotor arm.