Vibration under engine braking

[LAWLence]

Ever since I installed the Vorshlag nylon engine mounts, I have had an occasional vibration when lifting off the throttle. I assume this was masked by my soft (and partially disintegrated) stock mounts. No problems with the nylon mounts or the subframe that they're attached to.

It only happens under a light lift, perhaps every 1 out of 30 times and continues down the RPM range unless I apply a bit of throttle to smooth it out. This is on an S54.

The engine has conforti software on it. There are mentions of throttle transition map modifications compared to stock. Perhaps this wasn't as refined as it should have been? It feels as if the injectors are still running but there is no spark. I don't have a way to replicate it.

It's not really a huge issue, but with the stiffer mounts, it does send a nasty vibration through the chassis and is louder at the exhaust than a normal lift off the throttle.

Ideas?

[Serious]

That doesnt sound Like an engine problem. I would investigate the drivetrain

[flink]

Weird noises under decel can be due to the chains.

My s52 used to emit a distinct rattle from the front of the engine under decel. Put the car in neutral and blip the engine to 4k and you could hear it rattle as the revs fell through 1500-2000. Teh goog told me this is a sign of a worn hydraulic chain tensioner so I installed a (stupidly expensive) new one. And lo, that fixed it.

I still get a different crunchy/rattling sound under various decel conditions, even braking hard in a low gear. NFI what causes it and it's lasted 6+ hard weekends so shrug, wait until it gets worse or something drops off.

It appears that the S54 primary timing chain tensioner is very similar to the s52. It would be an easy experiment to borrow one out of a buddy's car and see if that fixes your car. There's a big single-use aluminum crush ring under the tensioner and they do wear out. Check for leaks afterwards - you might have to buy a couple of new ones.

It might be an issue with the secondary timing chain(s) or the oil pump chain too.

[RJME]

My car was experiencing exact same as you describe. Barely noticeable at first but then became a bit more frequent. No effect on performance.
I too assumed it was engine related.
Check Flex Disc/Guibo. Mine was developing a crack and was sending a vibration through the drivetrain.

[LAWLence]

Weird noises under decel can be due to the chains.

My s52 used to emit a distinct rattle from the front of the engine under decel. Put the car in neutral and blip the engine to 4k and you could hear it rattle as the revs fell through 1500-2000. Teh goog told me this is a sign of a worn hydraulic chain tensioner so I installed a (stupidly expensive) new one. And lo, that fixed it.

I still get a different crunchy/rattling sound under various decel conditions, even braking hard in a low gear. NFI what causes it and it's lasted 6+ hard weekends so shrug, wait until it gets worse or something drops off.

It appears that the S54 primary timing chain tensioner is very similar to the s52. It would be an easy experiment to borrow one out of a buddy's car and see if that fixes your car. There's a big single-use aluminum crush ring under the tensioner and they do wear out. Check for leaks afterwards - you might have to buy a couple of new ones.

It might be an issue with the secondary timing chain(s) or the oil pump chain too.

Thanks, I'll have a look under the valve cover after my event tomorrow. I revved it a few times in neutral and didn't notice any noticeable rattling noises.

Wanted to add: This happens most often around 3000-3500 RPM on the highway when I'm driving to/from the track when I lightly lift to match traffic speed. I've only noticed it happening once while on track.

My car was experiencing exact same as you describe. Barely noticeable at first but then became a bit more frequent. No effect on performance.
I too assumed it was engine related.
Check Flex Disc/Guibo. Mine was developing a crack and was sending a vibration through the drivetrain.

Thanks, I'll have a look at that right now as my car's in the air.

EDIT: It seems you're right about the guibo. It's not as bad as the one that was in my 323iT, but I'll replace it and report back. There are cracks around the three bolts facing the tranny in the direction of the engine's rotation. Thankfully, I think this is the last rubber piece on my car that needs replacing!



I imagine it's been like this for a while. I also did the transmission mounts at the same time as the engine mounts, so this totally makes sense.

[xsport652]

Wanted to add: This happens most often around 3000-3500 RPM on the highway when I'm driving to/from the track when I lightly lift to match traffic speed. I've only noticed it happening once while on track.

Been having the exact same problems with AKG 80A motor mounts, 95A vorshlag trans mounts. Checked torque's on everything in the driveline and nothing is out of whack. I have checked the guibo multiple times and it looked fine without any cracks, etc, but I'll probably replace it this winter when doing the clutch/flywheel just to check another thing off the list.

[VengeanceM3]

Same problem after I installed Vorshlag nylon motor mounts and their harder transmission mounts. Plan to replace the guibo, csb, and diff mounts this winter as well.

[LAWLence]

I've just been informed that it may be the harmonic damper. Being that this is an S54 (and I recall seeing several threads about it), I think this is the problem.

[nickdrivesm3]

I've replaced a flywheel and clutch assembly for vibration on decel, stock car though.

[PCarroll]

One of our guys had an S54 harmonic balancer go. It sounded like crap - metal rattling sounds just at idle in the pits.

[albrazzi]

I get that with RPMs falling through 3500 with only poly trans mounts (M44), I suspect it will get worse with Engine mounts also but when Im sure its that I can somewhat disregard it as an issue. Can you rule out as only the mounts by temporarily reinstalling OEM, I know its a lot of trouble but it would be good to know if thats the only cause.

[TostitoBandito]

Resurrecting this.

Did anyone ever come to any conclusions here? I recently installed Vorshlag 95A/80A motor/trans mounts and am having the same issue where I get a brief vibration when lifting off the throttle in gear. I first noticed it on the freeway and it felt almost like I was on a rough patch of road or a gentle rumble strip. At lower speeds it's more subtle.

I'll probably replace my guibo at some point soon, but I'm not convinced it's actually causing this. It's old, but intact by all appearances. I get the impression that this might just be a normal byproduct of the stiff mounts revealing all the varied engine/transmission quirks.