eric_in_sd

Didn't see anything in the forums about coil failure, so here's a new thread.

Exiting a moderately aggressive right hand turn, sudden CEL flashing for maybe one second, then steady on. Turning off ignition and back on - all was normal. Found pending fault P0305, cylinder 5 misfire. First time this particular gremlin has growled at me. Hasn't recurred, and the truck has been normal since. Even passed smog.

Changed the plugs ~50k miles ago; current mileage 145k. 2007 GL450.

The right hand turn could be coincidental, but it sure felt like punching the throttle triggered the misfire. Y'all have any ideas?

kombifan

I had this on my 2000 ml....

I would check all the connections first, check for loose plugs, wires etc.

Then go one by one and what you can afford to do. Check the spark plug first. If its clean etc.
The think about changing the wires and then think about changing the ignition coil.

It ended up being the coil for me. Will probably be $50.

eric_in_sd

Thanks bro.
Coils do sometimes fail; I'm not sure what fails but I'd guess it's thermal or oxidation stress. They can be built to last essentially forever, but it's a matter of cost. Since these coils are directly on the spark plug, there's no wire except the low voltage side.
I figure it's worth checking for something obvious, like a loose wire to the coil, but that pretty much leaves the spark plug and the coil. I don't see spark plugs being intermittent, nor actually causing a misfire unless they're full on broken, shorting out - so that kinda leaves the coil. I'll probably swap the coil on general principles.

kombifan

My guess its the stress and age......but beats me why one will fail and not the others.

If its not actually giving you any issues anymore, its probably senseless to pursue a ghost. I would wait till it pops up again or more frequently.
With mine, it would pop up every 2 weeks and I finally tracked it down after doing the plugs, wires (which needed doing anyways) and then deciding it was the coil.
Its worth checking the condition of the plug if youre in there anyway, just to check if there is any unburned residue on there!

No worries Mate!

eric_in_sd

Yeah, I'm hip to the frustration of ghost-chasing. However, I have to balance it with conservatism; my teen daughter drives the car solo, and reliability is important. I was able to score a "used" coil on Amazon Warehouse Deals for half price, so I went for it.
Coils do sometimes fail completely; while the motor would lose 1/8 its power, the engine would probably complain a lot.

I'll check the plug, though I'm still PTSD'ing from separating a plug's threads after over-torquing. The engine being an oil burner, that's definitely a possibility.

fabbrisd1

Frankly... the situation you describe is one d*mn good reason to check your engine mounts..... and at your mileage .. in a turn, throttle stabbed down... you're banging your engine down on that mount like a a sledgehammer..

eric_in_sd

Whoa - now that's a damned interesting idea. I'll check it out for sure.

kombifan

Umm wow.

That's your daughter's car?!😲

...are you looking to adopt?! 🙋🏽*♂️

Who am I to speak. I drove an expedition in high school....😳

Lol I'm sure the coil was a good deal. Their prices are too good to pass up sometimes. I would test it out sooner than later. That 30 day return policy flies by.

eric_in_sd

Ha! Trust me, as an '07 with 145k miles, it ain't no luxury aw-tow-mo-beel.

I'll probably swap the coil and then keep the old one around. Or maybe put the new one in the trunk as a spare in case it happens again out on the road.