Date: Fri, 28 Sep 2007 07:02:23 GMT From: Doug Schwarz <seenospamfor.address.edu> Subject: Re: Intermittent engine vibration
In article <46fbe943$0$8415$db0fefd9nospam.zen.co.uk>, "Charles C." <c.k.christacopoulos.removeme.nospamee.ac.uk> wrote: > Doug Schwarz wrote: [snip] > > Any other suggestions anyone? Charles suggested leaking vacuum hoses -- > > how would I check those? Could an engine mount fail intermittently? > > What you are looking for is a possible misfire. > > One way of checking for leaking hoses (sucking rather than blowing) is - > I am told - to have the engine at idling speed, and spray carburettor > cleaner liquid (gas) to the various hoses and connectors. > > If you work slowly round the engine, if you find a leaking (sucking) > point, the revs of the engine will increase. Okay, I'll try that when I get a chance. > Another possible cause of vibration would be a misfire caused by a > leaking head gasket. If (I guess) the misfire is bad enough for you to > notice the vibration then you should be able to notice a luck of pulling > power. It could also differ between a cold and hot engine, and > certainly under the heavier loads. I haven't noticed any lack of power. > Engine mount. Would have been my next suggestion ... but it should be a > lot more obvious or different with the car in motion. Accelerating or > decelerating would move the engine and change the vibration. Agreed and there is no correlation with acceleration or turning. > Engine timing out? > Anyone? How does the timing work on this model (sorry my knowledge is as > far as early c900s). I don't know. > Does it have points in the distributor or electronic gadgetry? No points so I guess that means electronic ignition. Nothing too fancy. In article <46fbec12$0$8415$db0fefd9nospam.zen.co.uk>, "Charles C." <c.k.christacopoulos.removeme.nospamee.ac.uk> wrote: > Doug Schwarz wrote: > > I have a 1995 900S with an intermittent engine vibration. It appears to > > be related only to engine speed and it comes and goes. Here are my > > observations: > > > > 1. I notice the vibration mainly through the gear shift lever and the > > gas pedal. > > > > 2. When it first started it would exist for an entire trip and then be > > absent for another entire trip. Now it seems to start and stop during a > > trip and the amplitude varies, i.e., it's not the same intensity all the > > time, but you definitely can notice when it's there and when it's not. > > > > 3. It feels and sounds a bit like a hole in the exhaust system, but the > > character of the sound does not change with the throttle. It will be > > present at idle. If I get up to speed, press the clutch and then rev > > the engine back up to the cruising rpm the vibration feels exactly the > > same. As a result I conclude that it's not related to the tires or > > other drivetrain components after the clutch and also not a hole in the > > exhaust system. > > OK, a different take. > > If it sounds like an exhaust assume it is exhaust related. It was certainly my first thought, but how could an exhaust problem be intermittent? > If you open the engine hood (bonnet) can you hear that sound? Anything > at the exhaust manifold? No, although I can't rev the engine with my head under the hood/bonnet. > A blowing head gasket (got to be blowing badly) would produce some > hishing(?) sound. If you took a look at the sparking plugs do they all > look the same (brown/grey colour). Is there one or two adjacent plugs > which are different to the rest (oily, black or wet). Too far fetched, > you should be able to tell from luck of power. I haven't pulled the plugs because I don't have the deep socket I would need, but they were changed 18k miles ago. No lack of power. > All I can say is have another go at describing the problem (using > different words). Thank you, Charles, for sticking with me on this. I'll list my observations being as specific as I can. I know there's nothing like actually experiencing the problem first hand. 1. 1995 900S, 2.3l non-turbo, 4 cyl., 113k miles. I've owned the car for all but 8k of those miles so I'm very familiar with the feel of it. Normally, it is smooth. 2. Went on a long trip (375 miles there, visited a few days, 375 miles home). Next time I drove the car (short trip to store evening of return) the extra vibration was present for the whole trip -- from starting of the engine to shut down both there and back. 3. Next day, no extra vibration at all. 4. Next day, extra vibration present for all driving that day. 5. Extra vibration gone for a while -- I thought (hoped) forever. 6. It progressed into an intermittent problem. Now it comes and goes during a trip -- perhaps several times or it might not happen at all or it might happen for the whole trip. These are just short, around-town, trips, 10-30 minutes. 7. Description of vibration: It feels and sounds a bit like a hole in the exhaust -- low pitch, feel it on the gear shift and gas pedal, don't feel it on the steering wheel. A passenger not touching anything might not notice it at all. An exhaust problem I would expect to vary in amplitude with engine throughput -- more gas, more vibration. This is *not* what I observe. Vibration seems to be independent of engine throughput, only dependent on engine speed. It happens when the car is stationary and is exactly the same as when the car is moving. It seems to increase in amplitude as engine revs increase, up to about 3200 rpm where it either peaks or at least levels off. The vibration is not random feeling. What I mean is that if the engine was misfiring randomly -- random sparks not occurring, say -- you would notice that randomness in the feel, it would feel jerky. That is not what happens. This vibration is very regular. It feels just like the normal engine vibration, but just at a greater amplitude. Does that make sense? That's about the best I can do. If you think of anything let me know, but I may just have to see if it gets worse or hope I can demonstrate it to a mechanic. The local dealer is about 25 minutes away so by the time I get there it may not be happening any more. I'd hate to have to leave it with them for a few days for such a minor problem. The car is quite drivable after all. But I worry that the vibration is indicative of something potentially serious. Besides, it's just annoying! Thanks, again. -- Doug Schwarz dmschwarz&ieee,org Make obvious changes to get real email address.
