Can oil mess up coils? - 95 M3 130,000 miles

[M_3_X]

Got my car back from the shop last Thursday after several maintenance items were taken care off, (idler/tensioner, belts, valve cover gasket, sway bar end links, RTAB's, power steering hoses and reservoir).

Overall car feels much tighter and quieter, only thing is I felt a slight misfire at idle (IE when at a stop light), other wise the engine feels strong as always.
He had reported that when they were replacing the VCG, the spark plug holes were completely filled with oil (where the smaller gasket pieces go for each sprk plug hole) obviously that's where the oil leak was originating; and they had to replace the plugs as a good measure (besides that they were not OEM).
I found just unprofessional that they gave me the car back idling a little rough AND didn't say anything about it. But I digress.
When I called he said that "the computer had to adapt to the new plugs" and drive it for at least 200 miles is this true or is he BS'ing me? I never heard about that (but again, not too familiar with OBD I cars).

Is there a possibility that oil sitting in the plugs holes for who knows how long can mees up one of the coils?
However, it was idling perfect before the VCG job and I've driven the car more than 200 miles now and still doing it so it's going back for resolution.

What do you guys think about the whole story?

[BayEmVay5]

"The Ecu had to adapt to the new plugs"??? i call B.S. on that one.

But to answer your question, yes, oil can damage/prematurely fail the coil packs as it can with any electrical device.
I had same issue with my E34. Idled a little rough, and on take off and acceleration at low rpm the engine would stumble slightly then take off. The spark plug gaskets were so brittle they broke when I took them off! and 4/6 plug holes had some oil in them.

Replaced the spark plugs and coils. Idles and drives like a champ.

[RisBMW]

May not need the whole coil.... might be just the connector boot which are available seperately and much cheaper.

[M_3_X]

Thanks, that was kinda what I thought. Now I guess the question would be, if a connector boot or coil is the culprit, why they didn't fail before when they had the oil pool in them?

[RisBMW]

With my car, it had issues which is when we found the oil had deteriorated the connector. Maybe on yours - since there weren't issues before - oil got where it isn't supposed to be when they removed the connectors to replace the plugs.... just guessing here.

[BayEmVay5]

Thanks, that was kinda what I thought. Now I guess the question would be, if a connector boot or coil is the culprit, why they didn't fail before when they had the oil pool in them?

Because magnets!

lol no, but my guess is that maybe the oil caused added resistance? which made the coil work harder than it should have to, to generate enough electricity to jump the spark plug gap, then eventually the coils wore out(still generating electricity but not up to spec)

[Da Infammus 1]

Oil can definitely cause coils to fail. It could've been holding on for dear life with oil on it and slowly deteriorated. I'd def replace my coils if I found a good amount of oil of them, because if they haven't failed yet the oil will most likely cause them to fail sooner than I wanted anyway.

[fun2drive]

The reason for the miss is that the boots are toast. When removing them and my guess is they were OEM they broke internally enough that it has an air gap it has to jump beyond normal.
They didn't do anything wrong except they were most likely trying to save you money since replacing them isn't cheap but cheaper than an hour of mechanic labor.

Replace all the boots plain and simple. Also 95's always have had issues with coil failure, 94's too.

Coils don't typically go bad at idle they fail under load when it is hot so my guess again is the boots...

[mgoods50]

Got my car back from the shop last Thursday after several maintenance items were taken care off, (idler/tensioner, belts, valve cover gasket, sway bar end links, RTAB's, power steering hoses and reservoir).

Overall car feels much tighter and quitter, only thing is I felt a slight misfire at idle (IE when at a stop light), other wise the engine feels strong as always.
He had reported that when they were replacing the VCG, the spark plug holes were completely filled with oil (where the smaller gasket pieces go for each sprk plug hole) obviously that's where the oil leak was originating; and they had to replace the plugs as a good measure (besides that they were not OEM).
I found just unprofessional that they gave me the car back idling a little rough AND didn't say anything about it. But I digress.
When I called he said that "the computer had to adapt to the new plugs" and drive it for at least 200 miles is this true or is he BS'ing me? I never heard about that (but again, not too familiar with OBD I cars).

Is there a possibility that oil sitting in the plugs holes for who knows how long can mees up one of the coils?
However, it was idling perfect before the VCG job and I've driven the car more than 200 miles now and still doing it so it's going back for resolution.

What do you guys think about the whole story?

This kind of BS gets under my skin QUICK. There is NO adaptation, PERIOD. Oil will cause coil failure- too much to type, but short answer is yes. Likely boots were hanging on for dear life, and when pulled out of that sludge pool, gave a bit. Yours are overdue for replacement. Boots SHOULD have been replaced, not plugs "good measure"- that's dumb. The boots are less than $10 each, and depending upon the plug you use, about the same. throw in a set of bosch 4417s, that's what I run with bavauto hiperf coils. the coils arent cheap, but they're a blast.

If you're stammering and stuttering around still- you probably have a misfire due to the crappy boots. Do yourself a favor and order a set from Autohausaz, pelican, or any supporting vendor and DIY. IT's not that difficult. you'll need a 10mm 1/4" drive socket set, a towel, a magnetic tray for the 10mm nuts, some dielectric grease for the plug tops / boot insides, 45 mins (way overstated) and a cold beverage.

THERE IS NO ADAPTATION- PERIOD.

Swap these in, then tell them they are FULL of $hit, you're not stupid, and you're taking your business elsewhere- your driveway.

and as far as the OBDI thing- they are less advanced, not more. the DME does not have to learn how to ignite air / fuel mixture again. And it sure as hell doesn't take it 200 miles to figure out anything. that shop person needs to be slapped.

Sorry for the longwinded response, but given what you've said- i think its warranted that you physically CHECK the wires going to the coils. Make sure they are seated properly in the harness, and make sure they are in ORDER. Cylinder #1 is nearest the radiator, and numerical value increases as you move toward the firewall. Cylinder #6 is nearest the firewall. All the coil wires are numbered, and should connect to the corresponding cylinder. Hurray for 1995's!

[M_3_X]

This kind of BS gets under my skin QUICK.!
Excellent info! Thanks everyone. I really don't feel like taking the car to the same place at all. I'll check the wires/boots/plugs condition myself this weekend, and I'll order six new boots to start. I bet they are the factory ones, since I don't see them in the maintenance history from the previous owner. If the problem persists I'll be coming back for more help!


Appreciate the help.

[M_3_X]

Excellent info! Thanks everyone. I really don't feel like taking the car to the same place at all. I'll check the wires/boots/plugs condition myself this weekend, and I'll order six new boots to start. I bet they are the factory ones, since I don't see them in the maintenance history from the previous owner. If the problem persists I'll be coming back for more help!


Appreciate the help.

Ok. Here is what I did:

Visually inspected coils, boots, wires and spark plugs; everything looked good and clean (not the oily mess that I was told) unless they cleaned things out really good, but I only found traces of oil at the bottom of the boots and around the edge of the plugs.
Took plugs out and they sure didn't look like new, they have must put in some used ones that they had laying around and made it sound like (hey we put new plugs free of charge!) since I had them out i went ahead and replaced them with new NGK BKR6EK so I could also rule them out.

Boots looked really good, no traces of oil or anything, contacts looked clean and free of rust. Rubber felt nice and supple. No visible cracks detected.
Wires looked good but a little hardened I guess by the heat, I guess they are the original wires. Firing order was good, connectors were good.
Coils looked clean, no traces of oil anywhere, contacts free of rust.

Idle still the same, slight misfire, no specific frequency, no CEL.

Should I go ahead and order the boots anyways? If one of the coils was starting to fail, shouldn't it throw a code? Is there an article around on how to test resistance on coils?

What you guys advice to do next?

[DLite]

I would go ahead and replace the coil boots.

[Moron95M3]

OP in the same boat (but a bigger misfire occurs above 6.5k rpm...which makes autoX'ing annoying).
Doing boots first (have new plugs) then will do coils if the issue is still there.

[LuxoM3]

What do you consider a "slight" misfire?

I've had both the OBD1 (95 M3) and OBD2 (96 M3) - they both idle funny... meaning, unlike say a Honda Civic which is like clock work - tick, tick, tick... the M3 goes rumble, rumble, rumble, hic... rumble, rumble, rumble, hic, hic...

There's almost an odd rythm to it.

Personally, I've found the *smoothest* idle from the NGK BKR6EQUP.
The worst idle... the Bosch FLDCR7 (something like that).

I'm at 207k miles with the original coils AND boots. I even had the plug wells FILLED with oil. I simply pulled the coil boots, sprayed with CRC Electrical chem cleaner, got a paper bowl and a pencil and dried out/cleaned. That was an easy 10k miles ago if not more. Not saying it's not an issue but... if I can go that long with the original stuff... well...

[M_3_X]

What do you consider a "slight" misfire?
the M3 goes rumble, rumble, rumble, hic... rumble, rumble, rumble, hic, hic...

:lol
Well, there is no rhyme or reason, it will sometimes do the hic thing more sometimes less, sometimes maybe a "rumble" here and there, and you can hear it from the exhaust too. No specific rhythm. It seems to do it more when is warmed up and no a/c.
The thing is that it was idling perfect before. So something had to happen/break when they installed the new VCG....

[DLite]

Could be a small vacuum leak. Check your oil filler cap, valve cover vent hose and connector, check all the valve cover bolts that they're all tight--should be 15 i believe(did they use new grommets?). Look down all the spark plug holes with a flashlight to make sure you can see the black plug hole gasket in each one. Basically check anything those guys would have had to touch.

[M_3_X]

Could be a small vacuum leak. Check your oil filler cap, valve cover vent hose and connector, check all the valve cover bolts that they're all tight--should be 15 i believe(did they use new grommets?). Look down all the spark plug holes with a flashlight to make sure you can see the black plug hole gasket in each one. Basically check anything those guys would have had to touch.
Will do. Yes they did change the gromments. What are the "black plug holes" you refere to? If they are the additional gaskets that go on each pair of spark plug holes, yes they changed those as well.

I think I'm going to try to do the coil test this weekend (the one you disconnect one by one individually and see if the idle changes....Anyone done that before?

[Stephen Max]

I find it hard to believe that oil can ruin an ignition coil, since there is no way for the oil to get inside the potted ignition coil to contaminate the windings. Oil contaminated with carbon does provide a path to ground, however, which suggests that a good cleaning out of the ignition boot and spark plug well will solve the problem (assuming the boot is still in good condition and the oil leak has been fixed).

Most coil failures (when it is actually the coil that fails) are due to insulation breakdown resulting in internal shorting. Heat is the enemy of insulation, and will eventually deteriorate the dielectric strength of the insulation until a short develops at the weakest point. This happens gradually, with the standoff voltage of the insulation system decreasing over time until it eventually equals the voltage required to make a spark at the spark plug tip and the coil misfires. This is why coils fail gradually. You can buy some time by decreasing your plug gap (if you're using single electrode plugs) so that less voltage is needed to create a spark in the combustion chamber. But eventually you'll have to replace the coil.