Trying to figure out a noise/vibration - E82 128i

[02Pilot]

My little 128i has developed a noise and vibration that I'm trying to track down. There are no stored codes and whatever is causing it doesn't seem to be affecting driveability. Car has 136k miles but has been well-maintained throughout its life.

The condition is throttle-dependent, and most noticeable at low RPM and large throttle opening. It seems more pronounced when the car is at operating temperature. It is a deep resonance, accompanied by a slight high-frequency vibration. In practice, I can reliably replicate it by putting the car in 6th at ~45mph and mashing the throttle. As soon as the throttle is closed, the noise and vibration cease.

My thoughts are:

1) Intake. This is an N51 car, so it has the three-stage intake manifold. Maybe one of the actuators has failed? But wouldn't this throw a code?

2) Exhaust. Maybe a small leak somewhere? It doesn't sound like exhaust leaks I've experienced before, but who knows?

3) Driveline. Possibly a U-joint starting to fail? Center support bearing? Noise doesn't seem to fit this though.

Just trying to brainstorm this out. Educated guesses, informed speculation, and wild conspiracy theories welcome.

[shadowpuck]

wow - that's going to be a tough one. i don't even have a good conspiracy theory to fit this......

[Critter7r]

My little 128i has developed a noise and vibration that I'm trying to track down. There are no stored codes and whatever is causing it doesn't seem to be affecting driveability. Car has 136k miles but has been well-maintained throughout its life.

The condition is throttle-dependent, and most noticeable at low RPM and large throttle opening. It seems more pronounced when the car is at operating temperature. It is a deep resonance, accompanied by a slight high-frequency vibration. In practice, I can reliably replicate it by putting the car in 6th at ~45mph and mashing the throttle. As soon as the throttle is closed, the noise and vibration cease.

My thoughts are:

1) Intake. This is an N51 car, so it has the three-stage intake manifold. Maybe one of the actuators has failed? But wouldn't this throw a code?

2) Exhaust. Maybe a small leak somewhere? It doesn't sound like exhaust leaks I've experienced before, but who knows?

3) Driveline. Possibly a U-joint starting to fail? Center support bearing? Noise doesn't seem to fit this though.

Just trying to brainstorm this out. Educated guesses, informed speculation, and wild conspiracy theories welcome.

Those were my first thoughts, in the order of 1, 3, 2.

[Critter7r]

Also, just for fun, make sure your spark plugs are tight. I had what I though was the beginnings of an exhaust leak for the about the past year or so. You could only hear it standing outside the car on the passneger side near the front tire. When I replaced my plugs as part of my 300k maintenance, I noticed one of them loosened up without any resistance on the rachet. Lo and behold, no more "exhaust leak" noise after that.

[02Pilot]

Also, just for fun, make sure your spark plugs are tight. I had what I though was the beginnings of an exhaust leak for the about the past year or so. You could only hear it standing outside the car on the passneger side near the front tire. When I replaced my plugs as part of my 300k maintenance, I noticed one of them loosened up without any resistance on the rachet. Lo and behold, no more "exhaust leak" noise after that.

I can confirm that they are because I just changed them last week, along with the coil packs, because I didn't know when they were done last and I'd noticed a little roughness at cold start and reduced fuel economy. The noise predates the change and has not changed since.

That said, I've had #4 on my 2002 loosen up more than once, so I know exactly what you're talking about.

[bmwdirtracer]

My prime suspect would be the variable intake. If a flap actuator is working, but the flap itself is fluttering and loose, you'd have no code, but likely have odd noises and a high frequency vibration.

Maybe put a stethoscope to the manifold, and have someone rev it a bit?

I do not know how the variable intake functions on your car, but I'm assuming similarities to those I am familiar with.

[02Pilot]

The intake seems like the prime suspect to me too. I don't know a lot about this particular system, but I'm going to see what I can dig up. If it's not a major hassle I'll pull the actuators out and have a look.

I did go under the car briefly to look over the exhaust and I found nothing even slightly wrong, so I think I can safely eliminate that unless it's an internal failure. Drivetrain mounts and guibo looked OK too.

[02Pilot]

I took a closer look at the intake manifold. The actuators are mounted centrally, with one up high right above the throttle body, and the other under the central plenum, sort of behind the throttle body. I coaxed the upper one out far enough to check the flap - it's nice and tight, so it's not the culprit. Access to the lower one is going to require removing the intake manifold. Are there any tips for getting the intake out relatively painlessly on the N51? It looks pretty straightforward, but I've been bitten by that assumption more than once.

[02Pilot]

Related question: Is there a way to actuate the DISA flaps in INPA/ISTA, as well as monitor their positions? I've looked in my little handheld scanner and I haven't found anything yet, but that doesn't mean it can't be done.

EDIT: I updated the software on the scanner and found test settings for Variable Intake #1 and #2. When I tried them, however, what I got was unexpected. With the engine running (albeit from a cold start) I got consistent ECU_ERROR_REJECTED messages, which was worrying. With the engine off, the test seemed to run, though I couldn't detect any indication of movement of either actuator. I'm not really sure what the tests are supposed to do, but none of this seemed helpful. Any thoughts about what all this means?

[Critter7r]

I would expect that the test would be ran while the engine isn't running. The actuators are already receiving input from [wherever] when the engine is running, so it seems like throwing more commands at them with the tester would cause an error.

[02Pilot]

That makes sense. In retrospect I probably should have run the test when I had the upper actuator out to see if it was moving the flap.

[02Pilot]

Update: Took the car to my trusted indy. He can't pin it down either, but he did narrow it to something in the driveline. Had it on the lift and ran it at speed while checking things with a stethoscope - the only thing he heard was a little noise from the diff (he says ring and pinion, not bearing). He also indicated that the oil looked a little grey, which isn't a good sign, as it was changed not that long ago. He changed it again for good measure.

He said drive it and see what happens. It may need to get worse in order to be able to isolate it. Not ideal, but at least I have a better idea what I may be dealing with.

What's the general consensus on these diffs? I haven't heard much about them causing problems or common modes of failure, nor had he, but it can't hurt to poll a wider audience.

[02Pilot]

Updating this in frustration. The vibration was bad enough that I didn't want to drive the car any more than I needed to - not exactly an ideal characteristic in a daily driver - and since we couldn't pin it down beyond it being in the driveline, I loaded the parts cannon and had my indy replace basically every consumable from the clutch back to the diff: clutch, flywheel, all the accessible seals, center support bearing, guibo, exhaust mounts, and probably a few things I'm forgetting. While he was in there he saw that the reluctors on the halfshafts were rusted, so we got a set of clean used OE replacements. Aside from the halfshafts, the only thing he found was that one of the U-joints was binding. He lubed it and got it moving freely again. Other than that, nothing was even close to needing to be replaced or showed any problems.

The result of all this was that the worst of the vibration, which as getting rather violent, was gone - great. Unfortunately, what was left was a higher frequency vibration, only from 45mph+, and again throttle position dependent; at highway speeds and constant throttle it's barely evident, but on or off throttle at 45-60mph it's more pronounced. There's a booming resonance associated with it. If I had to guess I'd say it sounds like a bearing grinding itself up. I can feel it through the chassis and the gear lever, but not the steering wheel. Having replaced so much, all that's left that fits the profile is the output shaft bearing, the U-joints, and the bearings in the diff. It's not affected by turning, so I don't think it's a wheel bearing (plus it sounds like it's coming from under the car).

So, a couple follow-up questions. I strongly suspect the current issue is the result of the same failing component - naturally, the binding U-joint seems the most likely culprit. First off, does anyone have experience with a U-joint acting like this? I certainly don't. Second, any best guesses as to which of the sources mentioned above might be the most likely culprit? Third, have I missed any possible suspects?

[shadowpuck]

random thought/question...

since it sounds like it needs load to make the sound or vibration - have you thought about sticking a camera (go pro or the like) and/or perhaps something like a chassis ear or such to listen to various things and see if you can nail it down?
or, maybe scope the diff and see if there's anything obvious?

based on what you've said i want to say diff, but i admit its a total guess at this point.

[02Pilot]

I have considered buying a Chassis Ear, but it seems like something that has a bit of a steep learning curve to use effectively. Didn't really think about a GoPro, but I also don't have one, so I'd be buying equipment either way. Not that I'm opposed to that, mind you, but given how much money I've already thrown at it, limiting further expenditure would be nice. But in the end it may be necessary.

[02Pilot]

OK, more frustrating updates. Just got home from the shop. Long story short, we decided that the driveshaft was the likely culprit after finding the rear U-joint bound up in one axis. New aftermarket driveshaft was sourced and ordered (BMW doesn't have replaceable U-joints on the factory part, naturally). It was installed this morning. The test drive and drive home revealed that there is still a vibration, but it has changed. It seems - pending further driving for more data points - that now the vibration simply increases with speed, whereas before it came in at around 45mph and faded away around 70mph. It is a similar vibration, felt through the unibody, but now seems more regular; with the old driveshaft there seemed to be a little variability and oscillation to it.

I'm thinking the replacement driveshaft may be out of balance, but I've lost all objectivity and good sense about this problem at this point, so I figured getting a few more thoughts on the problem would be a good idea.

[dworthy]

Nothing wrong with putting up on a lift and bring the car up to speed and observing the driveshaft.

Something else that comes to mind is flat spots on tires, you should see this while the car is up in the air.

[02Pilot]

Definitely not tires - I've had the same issue with two different sets. Getting it back on the lift is in the plan - I just have to see when he has time.

[Critter7r]

After hearing two or three anecdotal stories about vibrating new aftermarket driveshafts, I bit the bullet and spent the $$$$ on a BMW driveshaft for my E46 instead of chancing it to spend $$ on aftermarket. I figured the first one made it 300k, I'd likely not need another.

[02Pilot]

After hearing two or three anecdotal stories about vibrating new aftermarket driveshafts, I bit the bullet and spent the $$$$ on a BMW driveshaft for my E46 instead of chancing it to spend $$ on aftermarket. I figured the first one made it 300k, I'd likely not need another.

Unfortunately the first one (actually the second one) only made it ~8 years and maybe 100k miles. The original was replaced under warranty in 2013 while chasing a noise that turned out to be the exhaust (this was before I owned the car, but I have the records). The one we just pulled out has some serious rust on the rear U-joint. My faith in the factory part isn't quite as high as yours.

After lying awake most of last night trying to figure this out, I wonder if the replacement driveshaft was not set for precise length when shipped. We didn't check it before it went into the car, and I'm wondering if it's too long and pushing it out of line in the center. Shouldn't be too hard to spot running up on the lift.

[Critter7r]

The rear joint seizing on one axis was the culprit on mine, too.

And now that you mention it, I seem to remember some sort of clamp on the center splines that has to be loosened, and then retightened after everything else is torqued down.

[02Pilot]

The rear joint seizing on one axis was the culprit on mine, too.

And now that you mention it, I seem to remember some sort of clamp on the center splines that has to be loosened, and then retightened after everything else is torqued down.

I can't find anything in the TIS about the clamping collar, except to replace the ring if necessary. But without having measured the new shaft very precisely, I could see this easily causing the shaft to be out of balance. Stay tuned....

[Critter7r]

driveshaft.pdf

Release ring nut (1) with special tool 26 1 040 several turns. Installation note: Tighten ring nut with special tool 26 1 040. Tightening torque: 26 11 3AZ.

That's a tiny pic, but trust me, it shows a special spanner wrench going around a nut that tightens up on the splines.

[02Pilot]

driveshaft.pdf

Release ring nut (1) with special tool 26 1 040 several turns. Installation note: Tighten ring nut with special tool 26 1 040. Tightening torque: 26 11 3AZ.

That's a tiny pic, but trust me, it shows a special spanner wrench going around a nut that tightens up on the splines.

Thanks, that confirms it. And that's after everything else is tightened up? I don't have the special tool, but I'll see if I can make do. The torque given on the sheet that came with the new part is only 7ft-lbs, so it's not like it needs much. My indy can't get me onto a lift until a week from Friday (Friday the 13th - that bodes well), so I may be forced to try to get under there and get it far enough apart on stands in the driveway, which is pretty high on the suckage meter.

[02Pilot]

Quick follow-on question. I couldn't leave well enough alone until next Friday, so I ripped the car apart in the driveway. The only suspect thing I found was that the center support bearing did not appear to have been preloaded. I could see the witness marks from the original clearly a few millimeters forward of the new bearing mount. I can't find anything in Bentley or the TIS regarding preloading, but every CSB I've dealt with on a BMW requires it. Anyone have a quick yea or nay on preloading on the E8x/E9x chassis?

Also, I loosened the ring nut and wiggled the driveshaft around to settle it at the natural length. Didn't seem to move much if at all, but at least now I know it's been done.

Edit: Test drive shows it's better, but there's still some vibration as speeds climb past 70. I think the next thing is going to be to undo the bolts on the guibo and rotate the flange one hole (there's only three, so that's still 120deg) and see what happens.