How are you guys utilizing grease when installing new plugs and/or coil assemblies? I have had significant problems with misfires, especially on the front banks, after performing any work involving removing the coolant pipe from the top of the engine. Likewise with the rear when I've "oops" spilled coolant from the intercooler system. Presumably, coolant/water runs down and sits in the plug wells, causing an issue until it dries up. Potentially causing a permanent issue if it carried conductive dust down there with it, or damaged a coil/ignitor. I have had visible nasty crust/water evidence on the tips of my coils and/or spark plug hex every time I've pulled the coils. I would like to prevent future water intrusion if at all possible.

My question is, what have you guys had luck with as far as dielectric/silicone grease to prevent this? It's generally recommended just a light coating to ease boot removal...however, that does nothing to prevent water intrusion. Is anyone packing the red insulators clear full of grease? Is anyone taking it a step further and putting a bead around the outside of the coil tubes to prevent water/oil/whatever from running down into the plug wells in the first place? I toyed with the idea of cutting silicone tubing to slip over the coils and form somewhat of a seal against the head, but I feel there is too much variation in that surface to really seal it, even with something as conformable as silicone tubing. Water could still easily get down in there via the head bolt cutouts, etc. RTV is a no-go because it would likely glue the coil tubes to the head and break the delicate connections at the top of the coils upon removal. Silicone grease seems like perhaps the best solution. Opinions?

As a related subject, is anyone gapping plugs tighter than the .027-.032 or whatever that the plugs come with? Granted, that's an reasonably tight gap for a stock car, but 55w of max spark energy per bank is weaksauce. I have my wastegate actuators preloaded to the max and a race gas tune from eurocharged in place for daily driving on E85. My spark requirements are most likely considerably higher than even the average tuned car, and my misfires are definitely load and/or RPM related (will act up free-revving in park sometimes as well), which means to me ignition system problems. Either my coils aren't generating the voltage/spark energy necessary to jump the gap, or they are arcing somewhere other than the plug gap.

I would assume it was just the other original coil going bad if it was isolated to that bank, but I do get misfire counts on cylinders 1 and 3 under WOT as well, which have a brand new coil assembly and plugs around 2,000 miles ago. I am confident it's either water intrusion providing a lower-resistance path for the spark as compared to the gap, or that the coils simply can't produce the voltage required for my setup. Has anyone else with a tune or bigger turbos, or on alcohol fuel or water/meth injection had spark issues that were fixed with a tighter plug gap?

 

The only reason I could think of in our application that you wouldn't want to pack the insulators completely full of grease is that since they don't have a snap-on connector like typical spark plugs with wires...so the grease may well leave a sizeable layer between the plug contact and the spring, as opposed to being scraped off during wire installation. Theoretically, one wouldn't need to completely displace any air gap/possible water entry inside the coil tube itself if the tube to plug well was sealed externally. So I am now concerned that the application of silicone grease could possibly be doing me more harm than good and wanted to get some other input on how it can be used for water exclusion (as opposed to just boot lubrication), without potentially compromising coil-to-plug contact.

 

In for good discussion as I need to do my plugs/coils/ICM in the near future.

 

On a related note, does anyone know how the coil assemblies are laid out? There are 16 FETs or IGBTs or whatever they are for the coils, not 2 per cylinder as the individual replacements are always sold. Having a hard time figuring that one out. I think that would be 12 drivers, 1 for each coil, plus 4 extra for the ion sensing. I know that the coils have to have individual 180v drivers because the computer doesn't batch-fire the pair for a cylinder under all circumstances (there's I believe up to 10 crank degrees of offset at higher rpms/load? Perhaps due to current availability from the power supply for charging the coils...there could be an advantage to not charging them simultaneously...or it could just be a means of slowing the cylinder pressure rise for knock prevention as compared to firing both plugs at the same time, who knows).

I'm not sure it makes sense to me any way I look at it. I thought I had seen reference somewhere to the ion sensing being divided into groups of 3 cylinders. So that's 2 drivers per 6 coils on the 23v side...but each driver would either have parts of two different cylinders (which would make no sense at all), or they each drive the "A" plug or a "B" plug, and each have one coil from each cylinder. I guess that would have to be the way it is, but presumably that means the ion current sensing is applied as a waste-spark type system and the 23V gets applied to all 3 cylinders for a given driver simultaneously. Perhaps there is no ionization in the gap of the cylinders that haven't just fired so it doesn't matter, but it just seems kind of odd to me.

I really wish I could just do away with these coil assemblies and run GM DIS coils or something...but the computer will cap the timing advance at something like 11 degrees if it doesn't get the ion current sensing signal. So it would have to be a full standalone ignition controller to do that (or more likely a pair of them, given the fact we've got 12 cylinders to run). Which inevitably would get more expensive than just fixing/upgrading the existing coils. I don't see why alternate coils couldn't be driven from the existing electronics to retain the ion current sensing, but with different windings and resulting voltage that the module isn't expecting, it could really screw with the current sensing anyway.

Frustrating.

 

As a side note: It is not advisable to re-gap the iridium or platinum plugs, as bending the electrode may weaken it.

I run mine on regular copper electrode plugs, with no problems whatsoever; a befriended MB mechanic that at home builds all kinds of racing engines, i.e. adding turbos and home made headers, also only uses regular plugs (you can clean burn them by running at 3000 rpm for one minute).

The red inserts should be according to MB (mandatory!) replaced at every coil pack removal, but I wash them in dishwash, then inspect them with a magnifying glass, and add only a bit of dielectric to the inner tip for easy slide on. I have had misfires before; the high voltage fired right across to the tube, and left a small mark on the silicone.

Hope this helps.

 

I don't touch the electrodes. The advice that iridium shouldn't be gapped is based on the fact that they are a tiny, brittle electrode, and can easily break off or be damaged by a gap tool if prying between the electrode and ground strap to open them up. I see nothing different about sticking them in a vice or using a gap tool and tightening up the ground strap as compared to any standard plug. The construction of the ground strap is like any other plug, with the exception of a small platinum disc to prevent gap wear/erosion.

Don't take this the wrong way but that sounds absolutely insane to me, especially given the frequency of problems with these coils. Curious if your car is stock or tuned? It's enough of a chore to change them, I wouldn't want to be doing it very often. Copper plugs wear out really fast with a hot spark under boost, foul easily, and take higher voltage to arc due to the lack of a pointed surface (the difference is actually quite significant between a pointed electrode and a flat/rounded one, possibly even more so than the gap size). I run plain coppers in most of my other cars, but find myself changing them @ 10,000 mile intervals tops in a performance application. Hell, sometimes after a couple hundred miles or less if I'm in the process of tuning or something and the car has been way on the rich side. If it's working for you then great, but I don't think I'll be giving them a shot.

Exactly what started this thread. I saw arcing both ways on different coils. A couple down to the plug hex, and at least one had left a burn mark on the surfaces of one of the insulators. I haven't been able to find much information on MVQ dielectric strength as compared to straight silicone, but it seems to me that it's not that great if a spark would rather arc through 5mm of it than through the plug gap or to the plug hex. Straight silicone is supposed to be around 18kv per mm thickness, so we would be talking about 90kv of insulation.

IIRC, Mercedes says the coils deliver up to 32kv. So if we're going with the assumption that the grounded coil tubes are in fact to provide a close place to arc to in order to prevent damage to the coil in the event of an issue with the plug or plug gap, then it stands to reason that Mercedes would have actually designed them to provide less dielectric strength than the max output of the coils. The other possible assumption about the coil tubes is that they are just EMI shielding and Mercedes hasn't designed-in a relief path for the coil to arc to in the event of a plug issue. That may well be the case, since I don't know of other ignition systems designed with intentional alternate routes for the spark to take.

I am going to order brand new insulators, and try this one more time with this coil assembly. It was difficult to remove the insulators from my old passenger coil that I had replaced without damaging them, so it's reasonable to assume that having had this coil off at least 3 times myself, some of the insulators may be damaged. I plan on doing just a very light coat of silicone grease on the spark plug insulators themselves so I can be sure that it's below the contact tip and I don't end up with a 400v/mil insulation between the spring and the spark plug...which I think could be my current issue. I will also try the thicker coat of silicone grease on the lower outside of the coil tubes to hopefully form a water-tight seal around the plug well, and will report my results. It will probably be next weekend before I get around to it.

 

Mine is stock NA.
I don't use regular plugs to save money; the heat range of plat/ird plugs does not encourage cleaning fouling; they were just selected for emission reasons and labour cost to replace (if in-warranty). Note that MB recommends for the V12 regular plugs for countries where unleaded gas is not available. And yeah, 10 000 miles is about right.

I found long time ago that the split in the tube allows water in, so the plugs had been flooded in the well about 1/3 rd up the plug ceramic insulator.

To me the tube is only for EMI suppression.

BTW: pulling the coil packs is easy if you follow the MB procedure, i.e. removing the steel brackets that hold the O2 sensor harness connectors below (or just above the exhaust manifold) - a PIA.

If you don't do that, you will force the coil tubes.

Observe the MB instructions on torquing these bolts, they strip easily in the alu head!

 

It is a bit more difficult for me now because after the intercooler re-plumbing, I have very little slack in my intercooler lines and they cannot be disconnected without SERIOUS effort and most likely damaged parts. The coil can still be removed, but it is a pain. I am not sure what brackets you are referring to, as I don't recall there being any in my way. The bracket that holds a couple hardlines to the inside of the strut tower area is a pain in the butt if not undone, but apart from that it's just pull the airbox, turbo-intercooler pipe, and tilt the intercooler as far out of the way as possible. I'd have to refresh my memory on the passenger side, but the procedure should be mostly the same. You're right, it's no big deal, just kind of tight work, could probably have the coil pulled in 15 minutes a side.

The part that is really time consuming is pulling and re-installing all the plugs, and/or cleaning and re-greasing the insulators. That's why I think the copper plugs thing is crazy...not so much that they wouldn't be fine for the job at hand, but that they are going to have so much shorter lifespan. You're basically paying the same amount for 4-5 sets of copper plugs as you would be for the one set of iridiums (which should last approx. 100k given that they are dual precious metal plugs), you just get to do the labor a bunch more times. I mean we're not talking about a 20-minute job here, it's at least several hours per bank if you're taking the time to inspect/clean everything and anti-seize and di-electric grease each one, and are using a torque wrench.

 

Missed your ninja edit in my other response, lol. So stock NA is going to have radically different firing voltage requirements vs say a peak boost of 20ish PSI on E85. Considering the coils are the same and you're probably going to have less than half the firing voltage requirement, I probably wouldn't be afraid to run coppers on that setup either. But again, why change them more often than you need to? In my opinion, iridium/platinum or double iridium plugs don't have any downside other than initial cost (which ultimately isn't any higher long-term). Looks like factory fill for your car is a double platinum, one step hotter than the Iridiums in the TTs. I can see why they would want more frequent service intervals with leaded gas.

 

Update: the brackets also hold the heat shields below the O2 plug connectors.

 

Must be way different on the NAs. I don't have anything like that. My O2 sensor connectors are clipped to the back of the intercoolers, and the secondaries are clipped to a bracket just in front of the transmission pan underneath.

 

I am not sure if one of the issue I am having is exactly similar as yours but it is definitely moisture related.

Some mornings when there is alot of humidity in the air and dew forms, my car throws a check engine when I start the car. And basically the whole passenger side bank throw CEL code for misfire. It just runs on 6cyl at that point. I can feel the loss of power. If I warm the car up to operating temp, turn it off, then turn it on again, the car starts up just fine. Then the CEL goes away. I am unsure if it's moisture getting somewhere in the spark plug holes OR if it's the voltage transformer.

 

Got new insulators installed today. No improvement whatsoever. I think I'm gonna have to bite the bullet and buy a new coil on that bank.

 

While it won't always show your problem, you can do a simple check for high-voltage leakage.

Attach a long test lead between the shaft of a long screwdriver that has a good plastic handle, and a good engine ground. With the engine running, use the tip of the screwdriver to probe all around the ignition system. Any spark to the tip of the screwdriver shows a leak in the insulation, and/or a high-resistance spot downstream.

 

That's a good suggestion and has worked for me on other cars in the past but there's no way to do it on these. The coil tubes are grounded and are always going to be closer to the spark path than you can get a probe, since they encase it. Likewise, I've tried an inductive probe to see if I could get any information that might point me to a spark plug problem but they all read out the same when it's not acting up and I don't have any safe/repeatable
way to duplicate the problem when not driving.

 

Mistake Post - wrong thread.