[3.1L Z]

I'm curious why the misfire occurs. Why does it not occur under no tune but crops up with tuning? For example, I'm getting misfire on #4 on aggressive map but not on "drive". I've ordered new plugs and see what happens but curious why this occurs on a technical level.
steve

[Jeff@TopGearSolutions]

As your spark plugs age, your gap increases.

As boost increases so does heat.

As you increase power your engine is more sensitive to where things need to be "optimum".

On a low boost stock tune, there is a large margin for error. Tuning for optimum has a smaller margin for error. (error meaning components not in spec, i.e. large spark plug gap).

[gunmetalcoupe]

Originally Posted by 3.1L Z

I'm curious why the misfire occurs. Why does it not occur under no tune but crops up with tuning? For example, I'm getting misfire on #4 on aggressive map but not on "drive". I've ordered new plugs and see what happens but curious why this occurs on a technical level.
steve

The technical reason is as follows: Your ignition system works by having the ignition coils produce a high voltage pulse that produces a spark across the spark plug gap. The voltage required to break down that gap is a function of the gap size and cylinder pressure; as you turn up the boost, cylinder pressure goes up and with it the requirement for higher and higher voltages across the spark plug. Eventually the voltage required becomes greater than what the coil packs can produce and you get a spark misfire. As your spark plugs age that gap becomes wider and you will misfire sooner.

On some of my previous vehicles, cranking up the boost has always required me to close the spark plug gap; on the BMW plugs this is not an option.

[3.1L Z]

Originally Posted by gunmetalcoupe

The technical reason is as follows: Your ignition system works by having the ignition coils produce a high voltage pulse that produces a spark across the spark plug gap. The voltage required to break down that gap is a function of the gap size and cylinder pressure; as you turn up the boost, cylinder pressure goes up and with it the requirement for higher and higher voltages across the spark plug. Eventually the voltage required becomes greater than what the coil packs can produce and you get a spark misfire. As your spark plugs age that gap becomes wider and you will misfire sooner.

On some of my previous vehicles, cranking up the boost has always required me to close the spark plug gap; on the BMW plugs this is not an option.

Thanks, I just put new plugs in and out went the misfire.....

[AWD Addict]

I have 15k on my Stage 1 agressive, and new plugs were installed right when i first flashed it.

I had a misfire occur on cyl 4 a few weeks ago that only occurred when the DME was flashed. stock was fine.

Swapped the plugs, and I'm running the aggressive map again without issue (so far).

My question is, the plugs looked great! I expected them to be pretty torched. Is this normal? I couldn't even bring myself to throw them out.

Is this consistent with what others are experiencing? I'm pleased it wasn't something more expensive like injectors or coilpacks, but still, seems crazy to throw these babies out!



*keywords: cobb accessport stage 1 aggressive misfire spark plugs cylinder 4

[Jeff@TopGearSolutions]

Originally Posted by AWD Addict

I have 15k on my Stage 1 agressive, and new plugs were installed right when i first flashed it.

I had a misfire occur on cyl 4 a few weeks ago that only occurred when the DME was flashed. stock was fine.

Swapped the plugs, and I'm running the aggressive map again without issue (so far).

My question is, the plugs looked great! I expected them to be pretty torched. Is this normal? I couldn't even bring myself to throw them out.

Is this consistent with what others are experiencing? I'm pleased it wasn't something more expensive like injectors or coilpacks, but still, seems crazy to throw these babies out!



*keywords: cobb accessport stage 1 aggressive misfire spark plugs cylinder 4

The color should always be good even on older plugs but the misfire issue is related to the gap increase.

As the spark plugs age the gap increases. That's what's causing the issue.

Sometimes people can get away with just re-gapping the plugs in a pinch.

[AWD Addict]

Okay. Thanks. I was just shocked at how clean they look.

I'll look at gapping, but honestly, the plugs aren't as expensive as I thought, so I'll be doing this in the driveway going forward. Looks like a pretty easy job.

In other news, my intake ports are pretty dirty again. I think I'm due for a regular walnut blasting every 20-25k at this point.

[Lotus99]

Originally Posted by AWD Addict

Okay. Thanks. I was just shocked at how clean they look.

I'll look at gapping, but honestly, the plugs aren't as expensive as I thought, so I'll be doing this in the driveway going forward. Looks like a pretty easy job.

In other news, my intake ports are pretty dirty again. I think I'm due for a regular walnut blasting every 20-25k at this point.

I'm a total noob at where the intake ports are or how to access them... I'd love to know what mine look like. I asked the dealer what it takes to check them before actually doing the work, and they said they'd charge like $300 for that, since there's a bunch of stuff they'd have to remove to get to that point. But at that point, you might as well just pay up a few hundred more to have them cleaned, since they've opened things up already.

I've changed my own plugs though, so that much I can do. I'm wondering, is that what you're suggesting? That once you take the plugs out, you can check the condition of the ports?

I did a quick google search, and didn't see a DIY guide with pics on how to access them. Found this vid, but at this point, it looks like they've taken the top half of the engine off to do the work...

[JamesM3M5]

Originally Posted by gunmetalcoupe

On some of my previous vehicles, cranking up the boost has always required me to close the spark plug gap; on the BMW plugs this is not an option.

Not entirely true. You can either find an old wire gauge spark plug gap tool or buy a 0.024" drill rod for about $2 from McMaster Carr (or whatever gap you want to run) and use that as your gap gauge. Works great on new plugs when you may have a weak coil and don't want to replace it yet, or a tune with aggressive low end boost.

[3000GT MR]

spark blow out is what the issue is. The pressure in the cylinder is to high for the spark to bridge the gap. Dense air is actually an insulator. There comes a point where a bigger gap is necessary but so isn't the use of high power coils or a spark booster.

[VNeBLOB42]

Originally Posted by 3.1L Z

I'm curious why the misfire occurs. Why does it not occur under no tune but crops up with tuning? For example, I'm getting misfire on #4 on aggressive map but not on "drive". I've ordered new plugs and see what happens but curious why this occurs on a technical level.
steve

Dude it's right there on COBBs website.

http://www.cobbtuning.com/BMW-335i-x...ive-s/1200.htm