eric_in_sd

Got this error a while back; didn't recur, but bought a spare coil just in case, along with my single spare spark plug.

Error returned, but this time not self resetting. Changed the coil - whoops, no help. Changed the spark plug - whoops, no help either.

Saw there had been a pending left side oxy sensor error. Pulled out my iCarsoft i980 and, after poking around, found my way to the fuel and emissions system monitoring. At idle, left side post cat (FYI it's labeled TWC, or Three Way Converter) oxy sensor holds a steady 1 mV, while right side fluctuates around 750 mV.

Ordered a post cat oxy sensor Bosch 16747 and will brave installing it. Hope the cat didn't get messed up from the marginal oxy sensor and rich mixture.

gl450x164

eric_in_sd

Well, color me bummed. No help.
I pulled the new spark plug back out, and it's clean as when it was installed. Now, I didn't do any driving, but did a fair amount of idling, and so that's making me think it's a plugged fuel injector. I can hear the #5 injector ticking, sounds just like the others, and there are no fuel injector error messages - so it's a fine lil mystery.
What doesn't make sense is that the problem had such sudden onset. That doesn't seem consistent with an injector plugging or otherwise failing.
I ordered a used ebay injector - risk $20 bux - and will try swapping it out. Anything I need to know about that lil adventure?

BlownV8

When mine was around the 200k mile mark with similar symptoms, it was a faulty cam sensor.

eric_in_sd

That's a twist. Did you get a specific cylinder misfire? Hard for me to imagine the cam sensor affecting just one. Are you referring to the magnet modules that bolt on the front of the cylinder head?

BlownV8

Yes, I forgot which one but one plug was missing an electrode and it was a new plug with less than 1,000 miles. I was lucky that it did no damage to the engine.

eric_in_sd

Wait, so you mean faulty spark plug? That makes complete sense.

It sounds crazy, but I've heard all kinds of stories about people losing stuff inside cylinders. If it's small enough it'll just bounce up and down until finding its way out the exhaust valve. The combustion chamber is such a violent place that all kinds of junk can go in there and not cause problems. It's when you have a crappy air filter, and you get a steady influx of grit, that the engine wear really goes up.

About the detected misfires: I think the system detects the misfire by looking at pulses from the upstream oxy sensor. Depending on the timing, that's how it localizes it to one cylinder. 0300 is "can't figure out for sure which cylinder it is" and 030x is "it corresponds to cylinder x". Too bad the system doesn't seem to inform you whether it's a lean misfire (too little fuel) or rich (no spark).

I probably ought to replace my upstream sensors if possible, 'cause they're used to fine tune the air/fuel ratio. Anyone know if swapping those is a reasonable job? Do it without removing the exhaust?

eric_in_sd

Unreal. Changed the injector, the problem remains.

Will do the oxy sensor, but I don't understand why it would indicate misfire primarily in one cylinder.

alx

are you actually feeling the misfires?

it might not be cylinder #5 at all... move coils around to see if misfire cylinder # changes. it might.

Racin_fool

Do you have the tools to do a compression test on the engine? My guess is that you have a worn exhaust valve seat. A compression test and cylinder leakage test will help figure things out since it doesn't seem to be an issue with your ignition system.

eric_in_sd

Hard to tell, 'cause the open loop mode takes over so quickly and then it's all dog like.
Here are the plugs from that side. If I didn't know better, I'd swear it was #7 misfiring. I'll swap the new coil in #7 and see what happens. Pretty weird the system would mistake #7 for #5 though.
#8 plug looks a little hot.
This was after driving for about five miles in open loop mode, btw.

eric_in_sd

The compression was golden (like 185 across the board) at 130k miles; it's 150k now. I'll check the compression at some point, but the motor runs great otherwise.

eric_in_sd

I reset the faults and it definitely has something a little off when it's running closed loop - before it goes open loop. Hard to tell with a V8, though. Feels worse when it shuts off lambda and goes open loop, though. That's no surprise.

Put a new coil and plug on #7. No help. WTF.

That bank 2 upstream oxy sensor looks near impossible to get out without dropping the driveshaft or something. You guys know if there's a trick to it? I've got the sensors and, at 150k miles, it wouldn't hurt to change them. But the left side upstream is buried deeper than my grandma.

I wonder if fuel injector cleaner would help. Maybe it's marginal injectors here, there, everywhere.

eric_in_sd

I saw the tech bulletin regarding cylinder heads. Mine would have been in that range, but the cylinder heads were replaced due to rough running in late 2010. I always thought it was odd they were so hasty to change the heads because of "intake valve deposits".

MBNewbie2008

eric_in_sd

Well, I put a new coil and a new plug on #7; no help. I also don't think it is ignition related because the cat temperatures are about the same side-side. Unburned fuel should make the bank 2 converter run hot. Instead, it's somewhat cooler (when lambda goes off and it presumably runs lean). Running fuel system cleaner (PEA stuff); the variation across plugs is possibly indicating fuel injector issues. Plugs 1-4 are uniform and look good, in contrast.

It's crazy to think the coils are only expected to last 100k miles. Hell, they've got a minimal duty cycle; half that of a four-cylinder with one coil.

alx

do you have star/ das?

eric_in_sd

Nah, I'm reading with iCarsoft MBII. This thing seems to read nearly everything; what would you be reading with star? Freeze frame?

After about 30 miles, the fuel injector cleaner doesn't seem to be helping. It's a little odd that the injectors would be gummed up on one side and not the other.

alx

star/ das will allow you to harmonize ignition at idle. however, it is also used to pinpoint ignition problems.

the fuel injector cleaner doesnt work when the vehicle is running, rather when the engine is shut off hot and left alone (and the fuel/detergent in the fuel lines) to heat soak a bit

ItalianJoe1

Misfire detection is done by the crankshaft position sensor, looking for constant speed up/slow down between cylinder firing, and using the timing of the differences to determine which cylinder is misfiring.

Look at both O2 sensors on that side, does just one read stuck at no voltage and the other cycles? You should have B1S1, B1S2, B2S1, B2S2 or something to that effect. Look at both bank 2 sensors and compare the #1 pre cat to the #2 post cat. The second is only used to verify cat functions, meaning it should always read just a little leaner than the first, but they should cycle. If it's stuck one way, and they both are, the o2 sensors aren't the root cause of the issue, most likely. They also won't cause a misfire on one cyl. Agreed with above, move the coils around and see if the misfire moves.

eric_in_sd

Left it idling, hoping the lower flow and higher underhood temps would do more cleaning. Real hard to tell, but it seems like it's getting better. It still goes to open loop mode a minute or so after startup.
Before it goes open loop, I get the B2S2 reading somewhat higher voltage - 800mV while B1S2 is 700mV. Note that my B2S2 sensor is new, so that might explain the difference.
The S1's only show lambda and current (because wideband?) Both S1 lambdas are right around 1 when closed loop. The current hovers right around zero for both.

If there's an actual spark misfire, I'll be damned if I can figure out where it is; it's definitely not on #5 or #7.
I'm contemplating changing the #8 injector, but that's a pain - I could do the #5 without pulling out the rail completely, but #8 is tighter. Damn.
The codes are persistently 0300 and 0305. Not persistently any of the others.

You guys know any way to disable the open loop mode? It's a pain to diagnose with it regularly going open loop.
Thanks guys for thinking about this.

eric_in_sd

Well, I gritted my teeth and decided to check compression, not wanting to find out bad news. Pleasant surprise, cylinders are still kicking at 180 down the bank. #5 is right in line.

While I had the plugs out, opted to show my boy how the spark plugs fire, sticking a plug in the #5 coil. No sparkie.

Swapped out for the new coil - well, whaddya know. Sparkie sparkie.

Now - did it have multiple problems (fuel injectors dirty?) or was it that I needed to clear the DTCs after replacing the coil the first time? I figured the computer would self clear after every power down, but maybe not.

It's great to find the problem, but boy do I feel like a dummy.

BlownV8

The coilpacks are dirt cheap on the 450. I did the plugs and coilpacks st 200k miles. Should be good to go for another 100k or 200k miles.

cnpdmb11

Hi there,

My wife's GL550 (2009) got the same error this morning - "P0305/misfire in cylinder 5". Was your issue solely the coil pack? I've never replaced the plugs/packs on her car and it's got around 135k on it now. Any recommendations for which packs you used when you fixed yours? Thanks

eric_in_sd

Swap with a new coil on #5, clear the error, and see what happens.

The coils are dumb, so it is a mystery to me how they end up failing. They don't make 'em like they used to.

Bosch coils are made by Delphi, who probably was the OE supplier. Just don't get Chinesium.

The misfire errors are only reporting a slowing of the crankshaft when a particular cylinder should fire. It just means the cylinder wasn't making torque on its ignition stroke.

The fuel injectors are generally reliable, but they may get gummed.