Vibration coming from Engine?

[IanAtkins]

Dear All,

I have had persistent vibration problems as some of you will remember, and in advance of my meeting tomorrow with Terry Gates, I think I might have something...

There is a roughness at idle, which I thought had nothing to do with the vibration.

But, when I moved the revs up - in neutral - i noticed that at 1000, 1500, 2000 not only did the rough rhythm not go away, but it didn't change according to the revs, so not an uneven idle I surmised..

While driving the car from standstill, accelerating very slowly up to 15, 20, 30mph I noticed that it's the same vibration always following, which reaches a peak and starts coming through the steering wheel at 60-ish mph..

So I think I might have found the source of the vibration - the engine - and it's referring through the exhaust and transmission and then through the wheel...

Any thoughts?

 

[Eno]

Maybe the engine mounts and transmission mount to start with??? This is what come into my mind first...


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[gsxr]

Engine vibration is USUALLY failed, or failing, engine mounts. How old are the mounts, and are they OE (Genuine MB) or OEM Boge?

Shot mounts are usually most apparent at idle, not at speed, but you never know...

 

[IanAtkins]

Chaps, the engine mounts (+trans) were redone 15 months ago, with perhaps 7-8000 miles done since then. I don't know who made them, but they cost like $400 for the pair....

 

[IanAtkins]

and the vibration was occurring before and after the mounts were renewed..

 

[IanAtkins]

According to a gearbox specialist, it's possible that it could be the torque converter, but extremely unlikely.. he's going to have a look/listen on Friday to see what he thinks..

 

[gerryvz]

Hopefully they are good quality mounts, and the folks who replaced them didn't charge the MB list price for sub-par Chinese product that a lot of shops are wont to do.... a sneaky money-maker for them.

The rough idle is what I'd focus on.

First, has the upper wiring harness been replaced?

Second, have you checked, re-set, driven the car and then re-checked the codes?

Third, have you checked the ignition components, including the insulator disc behind each distributor? Wires, plugs, distributor cap and rotor, etc.

Fourth, have you checked for vacuum leaks? Has the engine been either been put on a scope (to check ignition siguatures), or attached to a STAR system to check live data and see if anything is out of the ordinary?

The rough idle IMHO is going to affect running and vibration.

Normally, with shot motor mounts, you'll see and hear/feel a vibration in the dashboard at idle.

Cheers,
Gerry

 

[gsxr]

Hopefully they are good quality mounts, and the folks who replaced them didn't charge the MB list price for sub-par Chinese product that a lot of shops are wont to do.... a sneaky money-maker for them.

+1. You can confirm by inspecting the mounts visually. OE/OEM mounts will have clearly visible markings that aftermarket/junk mounts do not have.

Converter seems like an extreme long shot, I wonder if you can unbolt the converter from the flex plate and push it back towards the trans, then run the engine (disconnected from the converter) to see if the vibration is still present?

 

[IanAtkins]

Gerry thanks, I'm going to tell Terry all that tomorrow - the vibration's not so much in the dash, more through the seat. I don't think I've had the harnesses replaced, and re insulators sounds right. I've had the distributor caps replaced a couple times... We'll do all the rest..

 

[gerryvz]

You can check the date on your upper harness yourself; there are instructions in a sticky on how to do this.

It's here: https://www.500eboard.com/forums/showthread.php?t=1784

Upper harness should be replaced as a baseline before ANYTHING else is done.

 

[IanAtkins]

Gerry, why do you think the harness is so crucial if all the electrics are working fine?

 

[gerryvz]

The upper harness is electrically connected to the fuel injectors and other critical places that directly manage and control the engine.

In addition, a deficient upper engine wiring harness is a well-known contributor to all kinds of nasty and mysterious engine running conditions, up to and including "frying" the engine computer(s).

And, having a "known good" harness is baseline to being able to identify and diagnose a poorly running engine. Having a good harness eliminates many potential variables and permutations that can be caused by various degrees of degraded wires shorting together in the bundle.

Trust me, a known-good wiring harness is ALWAYS the first step to ensuring a stable base-line of diagnosis. Even better, but not critical, that the ETA and lower wiring harness also be of known-good wiring.

That's why I put it as the first step.

Have you determined the age of your harness per the above posted instructions by GSXR?

 

[IanAtkins]

no but i'll do that asap, thanks again.

 

[IanAtkins]

Well, the harness is ok (dated 2004) so that's not the issue. I did a basic test on my way to the mech, which was to hold the car at 100kph on a descent and switch off the engine to see if the vibration was still there. It was - so I think that means that it's not coming from the engine? The mech told me also that the idle is fine.