I have tried to read up on this but haven't found what I'm looking for. My 94 Automatic has an idle issue where it stumbles a little. I just removed the three rear coil packs and found corrosive dust from top to bottom. The spark plugs were covered as well, but those are now replaced. Other than testing the resistance on the coil packs, is there another way to test these? And do these coil packs intermittently fail. I thought either coil packs work or they don't. Maybe this is the reason for my poor idle. Thanks guys..
Coil Pack Question
- Thread starter El-Cojonico
- Start date
If the long 'nose' of the coil becomes contaminated, this can lead to ignition current flashover external to the spark plug gap which results in a misfire. The ignition misfire occurs when the break-down voltage of this external path becomes less than the break-down voltage across the sparkplug gap. There will typically be evidence of these external flashovers such as carbon tracking on the internal nose and rubber boot of the coil.
However, I doubt that ignition misfires are the cause of your idle problem. The voltage required to fire a sparkplug gap increases as the density of the mix of gasses increases in the sparkplug gap. Gas density in the cylinder increases as engine output increases (larger throttle opening). If you are going to get ignition misfire because of an external flashover it will occur first at high engine loads. Problems at idle; but, fine at high engine load does not really equate to external coil flashover.
The only time it may be idle only is on a cold engine when you have accumulated condensation on the coil nose which causes flashovers which subsequently disappears as the engine heats up and the coil dries out. However, once hot the idle will be fine unless the coil has been damaged by the flashover in which case you should have a problem all the time.
You mentioned the sparkplugs being covered in corrosive dust. Is that dust just on the metal part of the plug or was it up the insulator? Crap on the metal part of the plug won't affect spark plug operation; but, is probably an indicator that you have a problem with the sealing gaskets on the coil covers which can lead to longer term problems if you are a keener that washes their engine regularly. Anything that appears on the porcelain of the sparkplug above the point where the rubber boot on the coil should seal against the plug is a problem and is likely an indication that the boot on the coil has failed. Since the boot is not separately available a new boot requires a new coil. When I install my plugs I lather the boot on the inside liberally with silicon dielectric grease to help seal the boot on the plug. It also helps to ease removal of the coil in 7 years because it reduces the tendancy of the boot to stick to the sparkplug.
Where the coil body rests against the head (around the mounting bolts) there are exposed coil laminations. If you have a moisture problem, I have seem surface corrosion on the laminations. Mild corrosion on the exposed lamination that can be removed with a scotch pad is likely a non issue (other than you probably have a coil cover gasket issue). If the corrosion is significant with evidence of migration to the laminations below and physical separation of the laminations, that can be a problem. It may not result in out right failure of the coil; but, may result in lower peak voltage capability. Again, this kind of problem would show up first at high engine loads, not at idle.
However, I doubt that ignition misfires are the cause of your idle problem. The voltage required to fire a sparkplug gap increases as the density of the mix of gasses increases in the sparkplug gap. Gas density in the cylinder increases as engine output increases (larger throttle opening). If you are going to get ignition misfire because of an external flashover it will occur first at high engine loads. Problems at idle; but, fine at high engine load does not really equate to external coil flashover.
The only time it may be idle only is on a cold engine when you have accumulated condensation on the coil nose which causes flashovers which subsequently disappears as the engine heats up and the coil dries out. However, once hot the idle will be fine unless the coil has been damaged by the flashover in which case you should have a problem all the time.
You mentioned the sparkplugs being covered in corrosive dust. Is that dust just on the metal part of the plug or was it up the insulator? Crap on the metal part of the plug won't affect spark plug operation; but, is probably an indicator that you have a problem with the sealing gaskets on the coil covers which can lead to longer term problems if you are a keener that washes their engine regularly. Anything that appears on the porcelain of the sparkplug above the point where the rubber boot on the coil should seal against the plug is a problem and is likely an indication that the boot on the coil has failed. Since the boot is not separately available a new boot requires a new coil. When I install my plugs I lather the boot on the inside liberally with silicon dielectric grease to help seal the boot on the plug. It also helps to ease removal of the coil in 7 years because it reduces the tendancy of the boot to stick to the sparkplug.
Where the coil body rests against the head (around the mounting bolts) there are exposed coil laminations. If you have a moisture problem, I have seem surface corrosion on the laminations. Mild corrosion on the exposed lamination that can be removed with a scotch pad is likely a non issue (other than you probably have a coil cover gasket issue). If the corrosion is significant with evidence of migration to the laminations below and physical separation of the laminations, that can be a problem. It may not result in out right failure of the coil; but, may result in lower peak voltage capability. Again, this kind of problem would show up first at high engine loads, not at idle.
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Ok, seems like another dead end, and I'm probably going to have to seek the help of a Pro at this point. Under load, (Automatic) in drive, at a stop light, the miss is worse. I also read that it is possible that at higher RPM's the miss might be slightly unnoticeable. Anyhow,I ordered 3 new coils. They'll be here next week (back ordered). Once installed I'll update you guys....I'm so frustrated. Oh yeah...to answer your question, only the metal part of the spark plug had corrosion.
Save the old coils. The pre OBDII coils are getting to be in short supply and somebody may have need for them someday. If you had some 'stuff' accumulating down in the sparkplug wells it might also be prudent to consider replacing the gaskets on the coil covers. They are pretty easy to stretch out of shape if care is not taken during assembly. I use lots of silicon grease on them to help them slide into place. Also watch that somebody has not accidentally switched the front and back coil covers. They still fit when reversed; but, do not seal as well.
The OBDII coils are common as dirt because they were shared with the Acura RL and TL of the 1995 - 2005 vintage. Quick tip - the front and back coils on the OBDII are the same even though the parts numbers are different. All you have to do is rotate the base gasket to turn a front coil into a back coil - or vice versa. For some odd reason only the NSX lists the front and back coils with separate numbers, the others have the same number front and back.
Unfortunately, the common as dirt and cheap OBDII coils will not fit under the early coil covers.
The OBDII coils are common as dirt because they were shared with the Acura RL and TL of the 1995 - 2005 vintage. Quick tip - the front and back coils on the OBDII are the same even though the parts numbers are different. All you have to do is rotate the base gasket to turn a front coil into a back coil - or vice versa. For some odd reason only the NSX lists the front and back coils with separate numbers, the others have the same number front and back.
Unfortunately, the common as dirt and cheap OBDII coils will not fit under the early coil covers.
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- 6 December 2018
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maybe your ignitor is going bad? maybe swap it with a good one?
I guess that's next. Does anyone know how to test the Ignitor?
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