If a plug wire is bad...
The Bull
Joined: Jun 2002
Posts: 3,578
Likes: 2
From: Grand Rapids, MI
Re: If a plug wire is bad... A couple things. If a plug wire is completely fried to the point that it no longer can conduct a spark you'll know it without even looking at the codes. The engine will shake violently and you'll be lucky if it stays running. Just unplug the wire and you'll see what that feels like. There's nothing wrong in trying that out for a brief moment.
If a plug wire is damaged, but still conducts you may find that it will throw misfire codes at low speeds. At higher RPM's I would expect that the wire will still conduct enough juice to cause a spark in the plug.
Keep in mind all H/C cars will typically throw some misfires, especially at idle. In talking with the guys at AutoTap, a modded car will typically register misfires on their software. As long as the misfires are fairly uniform across all cylinders it should be ok.
Misfires can also be caused by timing issues too. For instance, if the PCM is programmed to dump more fuel into the cylinder but the spark duration is not there you'll get a partial to no burn. If the difference is big enough you'll get misfires. I believe the opposite would be true as well, not enough fuel and all spark would cause that symptom.
If you encounter either of these two cases something is really wrong (obviously). This could be due to several factors too. Bad O2 sensors, loose ground wires on the cylinder head, etc. could all be culprits. A bad coil can also help out. Just put a continuity tester on the wire and see what happens. Move the wire to another cylinder and see if the misfire changes locations.
Also pull your plugs and check them out. Look for oil, bent or fused electrodes, charring, etc. Try moving those around too and see if the misfire moves with it.
Hope this helps. If you're using AutoTap you'll get some pretty good approximations on your misfires moving too. I use that quite a bit on mine and it helps validate changes pretty effectively.
If a plug wire is damaged, but still conducts you may find that it will throw misfire codes at low speeds. At higher RPM's I would expect that the wire will still conduct enough juice to cause a spark in the plug.
Keep in mind all H/C cars will typically throw some misfires, especially at idle. In talking with the guys at AutoTap, a modded car will typically register misfires on their software. As long as the misfires are fairly uniform across all cylinders it should be ok.
Misfires can also be caused by timing issues too. For instance, if the PCM is programmed to dump more fuel into the cylinder but the spark duration is not there you'll get a partial to no burn. If the difference is big enough you'll get misfires. I believe the opposite would be true as well, not enough fuel and all spark would cause that symptom.
If you encounter either of these two cases something is really wrong (obviously). This could be due to several factors too. Bad O2 sensors, loose ground wires on the cylinder head, etc. could all be culprits. A bad coil can also help out. Just put a continuity tester on the wire and see what happens. Move the wire to another cylinder and see if the misfire changes locations.
Also pull your plugs and check them out. Look for oil, bent or fused electrodes, charring, etc. Try moving those around too and see if the misfire moves with it.
Hope this helps. If you're using AutoTap you'll get some pretty good approximations on your misfires moving too. I use that quite a bit on mine and it helps validate changes pretty effectively.
