Date: Sat, 22 Sep 2007 01:49:24 GMT
From: Doug Schwarz <>
Subject: Re: Intermittent engine vibration

In article <46f40520$0$13942$>, "Charles C." <> 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. > > So it should happen with the car stationary. Yes, it happens when the car is stationary. > > 4. It seems to peak in amplitude at about 3200 rpm. > > Ignition, any vacuum pipes. There is a possibility that the vibration > is there after 3200 rpm but its frequency is such that you can't tell. Yes, the vibration is there after 3200 rpm, it just seems to peak in amplitude there. I immediately suspected an electrical problem of some sort because of the intermittent nature, but the service advisor said that the "check engine" light would come on if one of the spark plugs was not firing. > > 5. The other day I did quite a bit of driving around town on a hot day > > (about 82 deg. F) and the vibration was absent so maybe it's temperature > > dependent. > > > > > > I called the local dealer and the service advisor said he'd never heard > > of anything like that before. I didn't get a chance to talk to a > > mechanic. > > Does the car have a Direct Ignition cassette? :-) No, it's the 2.3L non-turbo and there is no mention of the DI with this model. > Sorry, I had to have mine replaced recently (1997 9000) with the > symptoms being mainly a misfire (there is vibration for you) and having > got the new one I have realised that the car was rough for some time now > ... but I could not tell. > > > One approach is to drive the car until it gets worse. > > :-( > Charles Thanks for your comments (and Graham, too). I get the impression that the vibration would be far worse if one cylinder was not firing at all, but I will investigate further. There doesn't seem to be any loss of power and the car is perfectly drivable -- it just vibrates. Any other thoughts, anyone? -- Doug Schwarz dmschwarz&ieee,org Make obvious changes to get real email address.

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