Flutter sound above 4000rpm
Posted by Earendil
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As the cold weather sets in, and time drags on, my engine isn't sounding smooth like a hungry little beast, and is lacking a little power. Sounds like it's time for spring maintenance
However, a new sound has started that I have NEVER heard before on my E30. It starts around 4000rpm, and stays until red line. Sounds sort of like sticking paper in a fan. The flutter changes with RPM, and goes away once the revs drop back down below 4000 or so. The sound can be heard in the cabin, which is where I first noticed it. My first thought was a loud injector, but I didn't think you could hear those IN the cabin. It also doesn't slowly come on, as if it's always present and gets louder. It definitional sounds as if it starts at a particular moment in the revs. Does this jump out at as something obvious to anyone? If not, I'll wait a little longer and do the spring maintenance, see if I can get her running smooth again before dinking around too much. ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles 
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I'll do that this weekend. Though, my motor mounts are new this summer, and as long as the fan is weighted right, an increase in speed shouldn't cause it to hit anything, right?
However, it did seem to start with the cold weather, so maybe we are getting some expansion/contraction issues under the hood with the chilly weather. I'm having this trouble with car work, where my job keeps me busy during all daylight hours, leaving me tired and in the dark if I want to do anything during the week. This is why I would ask here before checking the fan
Time or Money, why oh why can't we all have both? ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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Have you ever done a compression test? |
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This last summer I did a compression test. They were all beautiful.
Now, it could be a NEW injector noise, but I know what those sound like in normal operation, and it's not a loud version of those. I also know what valves sound like when they need adjusting. Both of those are really sharp sounds. This almost has a buzz to it. I'll see if I can find a place to rev the engine up tomorrow (not home early in the morn, not work) and get back to you guys with what I find. I'm just glad someone didn't come back with "I know that sound! That's the sound of a hole through the center of your engine!"  ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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Oh, I know that sound; its a hole through the center of your motor
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Viscous coupling? Is that part of the fan clutch or something else? I opened the hood and revved her good this morning on the way to work. It did sound like I had a cross between a really loud injector and above average decibel valves. However I could not get the flutter-buzz to kick in at any RPM (figures!). As long as she keeps running a little rough, and no worse, maybe I'll wait until spring maintance to resolve it. Get her running smooth, and adjust the valves. I had contemplated putting brand new injectors in her this summer, maybe not be a bad idea if one of them is being loud. Dad is a family practice doc. I'll see if he doesn't have an old stethoscope laying around  ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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The injectors are going to be noisy when the motors cold (did you say you replaced them) on older high mileage motors, that and piston slap is enough to give you cause for concern... but it's fine even if it sounds troubling. The fan does have a viscous clutch and can cause noise, is it tight and a bit stiff? Is the motors unevenness connected to the noise, time wise? If you get it (the noise) under power it might be an exhaust leak. Rick |
The Injectors were replaced with rebuilt ones about 2 years ago. I have contemplated putting in brand new 4 pintle design injectors now that I have more money.
In what way should it be tight? If I put hand down around where a blade connects, and push out away from the motor, I can hear/feel an ever so slight rocking sound. I can hear it far more than I can feel it. I'd say 1mm of movement or less.I paid really close attention to the fan blade and any noise I thought might be associated with it, and it seemed their was more noise than I might have expected. However I don't think it's the source of the problem. See below.
Friday night I went out to a friends house, and getting there involved a 10 mile stretch of highway that no one lives anywhere near. This was a good opportunity to play around with 3rd gear and high RPMs. What I noticed is that the noise kicked in more around 4500-5000 rpm, and was dependent on crossing a particular point. HOWEVER it appeared to have more to do with engine vibration, than it did engine RPM. Now of of course with an increase in RPM, an associated vibration would also increase, so it's sort of hard to tell them apart. With a clear and open road I felt safer ducking my head around to try and get a good idea about the location of the sound. It sounds like it might be IN the firewall, maybe right smack dab in the middle, around radio height. I could be way off, but I'm wondering now if my rough running engine is just causing something in the firewall to vibrate at a really high frequency? Anyone ever had something like this happening? On Saturday I did a good engine inspection, and it turns out my spark plugs were quite nasty. I did a little math and realized I had put a ton of miles on them, so went ahead and ordered a new round of spring maintenance items. Mother nature, getting wind of this move on my part, decided to interrupt our 50 degree weather with 10 inches of snow on Sunday. Doh! If it has anything to do with engine vibration or roughness, than I would think changing the vibration intensity could eliminate or modify the flutter sound I'm hearing. If I get the engine running smooth, and it is still there, I guess I'll start looking again... ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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Exhaust gasket? I don't suppose you mean #3 in this picture, do you? [www.realoem.com] Or, upon further looking, perhaps you mean #8 in this diagram? [www.realoem.com] Certainly with all the drive shaft work I removed and attached the exhaust system at the point where the #3 gasket is. However when all the work was done I sealed that up really good...at least that was the intention
However spot #8 has never been touched or examined by me. It is also hidden away on the opposite side of the engine from where one would naturally stand in order to rev the cable. Certainly any noise from that location would have been masked to some degree by the injector noise and the valves. I'm going to have to give this a close look. Thanks for the tip, Peter, and to those poor souls who originally had the problem! Is anyone aware of a slick trick for detecting an exhaust leak, besides listening for the sound it makes? ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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The triangular gaskets #3 and #8 are the same parts, fitting between the top of the two exhaust pipes and the flanges of the two exhaust manifolds. If you've had that apart before while working on your driveshaft then it should still be relatively easy to replace those gaskets. The exhaust leak could potentially also be coming from the gasket between the exhaust manifold and cylinder head, part #6 in the second diagram. That's not quite as easy to replace because the manifold studs are probably rusty and they can be a beotch to get loose. |
One trick to keep in mind is using different size box wrenches to work on these cly. head exhaust nuts. The last time I did this I used wrenches from all of my sets; whitworth, american and metric (all six pointers), the heat and cooling, rust and wear will actually make these nuts smaller and they will change sizes. You're looking to just move them back and forth a tiny bit at first, once you've done that you're home; it just takes time and patients (and a good penetrating oil). Rick |
I wince a little bit here as I question you, but are you sure those are the same seals? If so, than perhaps I have a modified exhaust manifold/pipes. On my car, you have the 6 output pipes which I believe I are shown in the second figure, and sealed by #8. Those attach to a piece that takes 3 pipes each and narrows it down to one pipe, such that I have two pipes. Those two pipes are then show in the first diagram, and are sealed by #3. So without having my car in front of me, I'm pretty sure I have two different sets of seals, one of which is 18 inches further "down pipe" than the other. It would probably help if I could explain using technical car jargon for this stuff
But to try and explain again without diagrams, I have taken everything apart and resealed it at the section where only two pipes attach/separate, with each pipe having 3 bolts. No other seal has been touched by me. I looked on google images for a picture of the M20 exhaust manifold and couldn't find one. I'll snap a picture of mine tomorrow morning and post it. ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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You forgot the vice grips! After removing and attaching my exhaust pipes a half dozen times, those poor rusted nuts started to completely fail. I replaced them with brand new ones so I should be able to use a single wrench on them the next time ;-) Of course, I am talking about #2 in this diagram... anything further upstream I have not touched, and I assume will be just as bad or worse. ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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Well, this does not cover enough cylinders, but kind of explains what I'm talking about.
I have replaced the seals that would sit near the bottom left, where there is only a 2 pipe seperation. I have not unattached or replaced any seals near the top (where I would have 6 pipes), and I assume that is where Peter was referring to when he said a leak near cylinder 5 and 6? I'm sorry if the real OEM diagrams I chose did not represent what I was actually talking about, and thus were confusing. ----------------------------------------------------------------------------------- 1989 - E30 - M20 - Manual. Approximately 270,000 miles 2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles
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You'll wince a little more when you look closer and notice that both of those have the same Part#: 11761711717. 
#3 and #8 are both pointing to the triangular shaped gaskets which fit between the top end of the two exhaust pipes and the bottom flanges of the two exhaust manifolds, fastened by nuts on three studs. I think you must have been referring to #6 in the second drawing, which is the gasket (1 of 2) that fit between the exhaust manifold and cylinder head. That gasket includes an integral heat shield to protect the ignition wires from the hot exhaust manifold. I'm not convinced that your "flutter" is an exhaust leak though, not if you only hear it at 4000 rpm and up. An exhaust leak would be puffing away regardless of rpm, but most noticeable when the engine is heavily loaded. It would be relatively quiet when coasting off-throttle, but puffing loudly when you're hard on the throttle with the engine straining. An intake leak would be loudest at high vacuum conditions, such as at idle or if you let the throttle snap closed at high engine rpm. Is there something flapping loose that could be buzzing in the airflow from the radiator fan? What condition are your engine mounts in? Try wedging a prybar under the engine or lifting the engine with a hydraulic jack and piece of wood under the oilpan and see if your rubber engine mounts are still firmly attached to both the engine and the suspension crossmember. If one or both of the engine mounts have let go, the engine can move around by a surprising amount within the engine compartment. When that happens the radiator fan may be coming into contact with something that it really shouldn't be touching. On my 90 325i the fan carved a nice circle into the back of the radiator. On my 86 325e the pulley on the power steering pump sliced through the lower rad hose. Another possible source for a fluttering noise may be a piece of paper or leaf caught in your heater blower fan... |
I agree, exhaust leaks are really distinctive (sounding and smelling). You could try a simple (and cautious) power brake to see if the motor lifts (hood open and secured with a stick) in first and reverse. Ferdy's method of the crowbar is safer but power braking is easy and quick, just be careful. Rick |
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