Multi-cylinder misfire, rough idle, stalling...
 

Hi folks; I'm here to challenge your online diagnostic abilities. ;)

What it is: Rough idle, low/no power, hesitation, stalling
Codes: Misfire Detected all cylinders except #4, Cylinder Deactivation System (Bank 2); codes pulled from Bosch Enhanced ODB I & II Scanner at local parts store
MIL: Engine light, static and/or flashing

E70 N62 108k miles. I've had none of these issues before now except a rough idle at startup about 2-3 months ago. Stopped and restarted, then it was fine.

What it is not: spark plugs (replaced at 103k), coil packs (replaced yesterday), CCV/pressure regulating valve (replaced yesterday), battery (new Dec 16), oil leak (nothing obvious, gaskets/seals replaced at 103k)

I'm wondering if I may have a fuel pump issue. Can someone suggest another likely candidate part for R&R? Or something else to consider/check?

Thanks in advance for your comments.

Wild azz guess here but a vacuum leak that is throwing a bunch of stuff off?

Cylinder Deactivation System?? What is that?

I believe that is when the DME detects a dangerously lean situation and turns off the firing of that cyl to protect the motor. I think. Fuel pump seems a reasonable guess. Not sure how to trouble shoot from here. Pressure gauge perhaps?

Just a wild guess here as well. Have you checked the Vanos solenoids? I just brought my X5 in and the dealer replaced both. No more rough idling. It was to the point where it was close to stalling at times.

Next I plan to walnut blast the intake valves with almost 80k miles and replace the tensioner pulley.

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Depending on the particular codes generated, you might have a short in the wiring harness to the Mass Airflow Sensor. Limp mode and rough running are possible symptoms; but more so the limp mode, and severe warnings on the display. There are about four or five specific codes that relate to this issue, and you need to know the BMW specific DTC codes the car is giving you and plug them into Identifix or something like that....it will point right to a TSB on this. Some of the codes on this issue, (if that's what you have) refer to ECM failure....but don't let that scare you. I think something more advanced than a generic OBD II scanner might give you more info. If you can get access to an Autologic or a Launch that would be good.

For some reason, this harness is prone to melting and shorting out. Due to the frequency of this issue, BMW sells an inexpensive harness repair kit, that's basically a connector with about two feet of multiple wires attached, about 2/3rds of which has a harness cover. Splice it in carefully and you're done.

The N62 engine is prone to vacuum leaks and is also very sensitive to them when they occur.

I would start by checking for vacuum leaks using a smoke machine. I made one from a paint can and glow plug with a wick into mineral oil. Then I used a fitting in the lid for air pressure (3psi) in and a second fitting for air pressure/smoke out. Hook the air/smoke line out to the air intake past the MAF with a larg PVC cap that fits snug (I wrapped duct tape around the cap to gain the diameter I needed and threaded a fitting into the cap for the airline). Check YouTube for ideas on building your own smoke machine.

One other thing to check would be the injector for the cylinder. Swap it with a known good one and see if the misfire follows the potentially bad injector.

Lastly, if you haven’t found the problem, you may want to do a leak down test of that cylinder to check it’s overall health.

I had an E53 with an N62 that needed an engine replacement at 52kkm and had misfire which was undiagnosable at 160kkm.....I sold the lemon to a wholesaler.

Nice tiip..Thx

I just had a vacuum leak on my 325xi and it will exhibit the symptoms described by the OP. But searching for a problem with a single cylinder injector or coil pack is a waste of time when you have 7 cylinders misfiring. You don't get all injectors failing at once unless you have VERY bad fuel, nor do all coil packs fail at once. Unmetered air leak is a great place to look though.

Agreed! I misread the original post and thought only cylinder #4 was misfiring. My guess would be vacuum leak.

glenwyatt, many thanks for the suggestions! I think I've found the problem, but I don't know the cause...

I pulled the car from the stealership so I could verify/confirm the "cracked" manifold that they mentioned. Low and behold, looks like a couple of holes @ #8 intake (not to mention the "toasted" internal; see photos). Question is, how could this happen? How could it have been prevented?

It should be noted that the mechanics could not have seen this from outside inspection as it's clearly between the #8 runner and inner manifold housing. Smoke test showed a leak near the rear of the manifold, but my thought was 'gasket leak.'

Plastics crack....fact of life. The interesting thing is all the carbon buildup in that runner. I guess maybe it has something to do with the vacuum leak but I’m not sure. Glad you found your problem. I know how frustrating issues like this can be. Report back and let everyone know what the end result was when you get it back together.

Just to clarify, that's not carbon buildup in the runner; it's scorched/melted plastic. Difficult to tell from the photo and with the black plastic of the manifold.

WOW!!
I would probably do a leakdown test on at least that cylinder. The only thing I can think of is a grossly leaking intake valve which is allowing hot combustion gassed to migrate back into the intake track on the compression/ignition stroke, but this seems unlikely. I would try to figure out the cause before potentially destroying another intake manifold. Please report back with your findings....very interested in finding out what caused this.

Might want to look at this too.
https://repairpal.com/hole-in-intake...old-plenum-107

Interesting. Thanks Glen.
I have an injector on order to replace #8. Wondering now too about the cat :dunno:

What do the back of the intake valves look like? Are they carboned up on that cylinder?

Nope; they look like all the others, relatively clean.

Agree on all points...from the wow, onward.

Manifold aluminum "hold down" inserts are not captive
 

Found the cause of the damage...

As I was putting things away while I wait for replacement parts, I noticed something odd about the manifold that I removed. Two of the 10 aluminum "hold down" inserts were missing. You can see one of them is not were it should have been in my previous post's pic. I climb onto car and peer into cyl #8 and see the insert shown below with it's rim stuck under one of the intake valves (note the "chatter" marks on its rimmed edge). Then I start removing the paper towels that I stuffed in the other inlets and find the second missing insert in cyl #2. This one was just lying in there because it probably fell out as I was taking the manifold off (yesterday). The one in cyl #8 must have fallen out as I replaced the manifold some 8 months ago when I did my AGA coolant pipe and valve gaskets. Hadn't noticed it before (obviously), I but figured these inserts were captive. They clearly are not. If you bump or jostle the manifold, they can fall out.

Other than burning holes in my intake manifold runner, I'm not sure at the moment what other damage there may be as a result of this.

Kudos to glenwyatt for deducing a possible cause (hot combustion gasses migrating 'backwards') for the burnt intake runner with limited info.

Hopefully the intake valve and seat is not damaged. A quick test- With both intake valves closed try putting a small amount of gas around the valves/seats and over time see if it leaks past into the cylinder. If it is sealed then soak up the gas afterwards. idealy, a leakdown test will tell you if the valves or other issues are now present in that cylinder though.
Good detective work BTW!