Engine vibration - The seemingly endless saga
 

So I've had engine vibration from my E55 for going on 4 months now. After 4 trips to the mechanic and replacing components on every trip, I have yet to completely solve the issue. I still have very noticeable vibration/shakes on cold start. While revving the engine in park, there is a consistent, sharp, quick vibration as the RPMs reach the normal idle level. Once the car is warm there is always a VERY minor vibration, though overall the problem is much less severe. I should mention the idle is perfect, there is no surging or bouncing in the engine idle RPM. The car shakes but the motor is smooth as silk. I don't get it.

Since this issue has begun, I have replaced many things to no avail. Though in all honesty, I'm still glad I am on top of the preventative maintenance.

First trip - 100k mile tuneup. (Plugs, wires, oil, oil filter, air filter, transmission fluid)
Second trip - Fuel filter & fuel pumps. Cleaned intake & throttle body.
Third trip - Pressurized fuel system cleaning & in-tank cleaning agent for 400 miles.
Fourth trip - brand new motor mounts and transmission mount

I'm running out of ideas... :confused: There are no fault codes, check engine lights, nothing. What am I overlooking? Though possibly a separate (or maybe related) issue, at times the car has a very rough supercharger engagement with chirp.

i have a similar issue on my s500.

My current plan is to pull the intake and fuel injectors for cleaning, as well as the EGR. also replacing all intake related items (gaskets, vac lines, etc) at the same time.

Its extraordinarily frustrating.

Have you considered the crank pulley/harmonic balancer?

This will probably be my next plan of attack

if you have access to DAS. you can go into the ECU and pull up the fault counter menu. This will show fuel / misfires issues / on each cylinder that are in the frequency of less than 3 times in a 10 sec period. Usually these low misfire frequency do not trigger a CEL.

I don't myself but the indy mechanic I take the car to does. When he hooked it up on my first trip in, he told me there were no fault codes. The car shakes/vibrates but the RPM needle never moves. Plus, the car now runs stronger than it ever has when you give it some throttle. I have no reason to believe the motor is running at anything less than 100%

yes there will no be no fault codes.
the fault counter is different from the fault memory in the ecu

i'll see if they have access when I make the next trip, but I have a good feeling that the car is not missing. if it is, what could be causing it that I haven't already looked at?

what mods do you have?

nothing, car is stock

in the DAS menu there will be and item check for smooth running of engine. try to see if that helps

alright i'll mention it to the shop. does anything come to mind hardware-wise that could be the problem?

Shardul is exactly right.. I had a very similar situation, dealer could not figure it out.. My indy howerver did, I had 2 slightly misfiring injectors.. Good luck, I know what a pain in the arse this is..

Alright, I'll pull the injectors this evening instead of waiting to take the car into the shop and having a computer tell me they're bad, if that's the case.

As mentioned earlier, is it possible the harmonic balancer could be causing this?

even if you pull the injectors, visually you wont be able to tell if they are bad

ok. shardul, is it worth checking to see if a worn harmonic balancer could be the cause of this? want to cover all the bases..

visually if the crank pulley does not have a wobble you can rule that out

cool i'll check that out tonight

where would you find that in das?

thanks

I seem to be running into indies using aftermarket STAR wannabes without enough knowledge to find this stuff. its frustrating.

anyone in NJ have star and would be willing to help?

took a look at the pulley and it appears to be fine. so i'll rule that out.

on the drive home I had some surging coming up to a stop sign. as the car in front of me drove away from the stop sign, i let my foot off the brake and gave a tiny bit of gas to creep up to the line. as I let my foot off the gas - the motor softly surged/lurched forward twice as if the car was getting gas when it wasn't supposed to.

i confirmed this when i got home. while revving the engine, i noticed the shaking/vibration occurs as the RPMs are falling and the throttle is closed. on one rev, the vibration came at approx. 2.5k rpm and at idle, consecutively. i don't know what to make of this but hopefully you can.

thanks

Do a compression test.

That will confirm the mechanical health of the engine.

If you have low compression in a cylinder it will not idle smooth as it should and you can feel it at other times.

G

That's a scary thought...Might be worth checking after I can rule out fuel & ignition issues. Keep in mind I have no check engine lights or fault codes. The car runs very strong and smoothly when accelerating (save for supercharger engagement, which could be caused by this root problem), it's just the part-throttle, idle, & on/off throttle response that is rough.
\

Honestly I think Shardul has told you exactly what to look for, everything you are describing here is indicative of a injector gone wild (well slightly clogged or sticky). My many years building cars I have never seen this level of deep computer integration like I have on the Merc vehicle with STAR or DAS etc etc and in most vehicles you will have to guess what Shardul just told you to look for.

PS if you wanna see if injectors have anything to do with it, put a full bottle of Techron or Seafoam into your less than half tank of gas, drive for a day or two and see if the problem gets better. If it does, then do what Shardul said and take that injector you identified and have it cleaned or repaired

clean the inside of the throttle body ...careful not to break the tab on the intake Y ....tab on bottom and on the top...good luck if you figure it out come back and tell us so it is not a dead thread... please

Thanks for the input. The injectors will be my next effort in tackling the problem.

Thanks and I will be sure to report back. I already have cleaned the TB but I'll hit it more thoroughly this time, maybe removing it from the manifold and cleaning the backside as well.