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Discussion Starter #1
I have a 2006 M6 which is a great car except: The engine vibrates like it is out of balance on anything over about 30% throttle. On decel or out of gear, it is smooth as can be. But put it in gear and get into the throttle and at about 3200 it shakes like it has the wrong pistons in it. You feel it in the shifter and the clutch pedal. It has to be a significant imbalance in the combustion or cylinder loading to shake like it does. The local dealer's best heavy mechanic has an auto and says his is much smoother, but that does not even come close to answering the question. I love the car and want to solve the problem and would prefer to keep the local mechanics out of it. Hey, what could be more fun that a car that we have to test at WOT? I'm looking for serious suggestions on how to solve the problem. Again, it is not static balance or it would vibrate the same irrespective of throttle position. I drove blown gas hydros for many years, so I'm not expecting a Lexus shifter. Something is wrong!
 

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Missin' the Goat
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625 Posts
Is the vibration violent or a little more noticeable than another person's GTO? I had the same thing happen but not with my Goat, it was when I was a teenager and jumped my parents car off of a hill. I ended up shattering a motor mount and a cv joint. It was fine when I was sitting in idle, but as soon as I gave it gas, the engine started jumping around. I'm sure that your's isn't anywhere near how bad that was, but maybe the engine is off balance somewhat. I've never heard of a problem like this, so I'm sorry that I'm not a great help with this. I'm thinking that you should definitely take it back to the dealer so that they can take care of it. It should be on their dime, not yours.

Jerad
 

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Discussion Starter #3
The car only has about 1500 miles on it and I did not notice it until the first time I got on it after about 500 miles. I've driven two other M6 cars and while the vibration was there, it was no where near what mine does. My biggest problem with the dealer is that I think there is 50 times the knowledge on this forum than there is at the dealer. I really don't want to have them try to figure it out. Unless the ECM throws a code, they are at a loss. The only thing I've thought of is putting it on a dyno and checking the manifold temps at each cylinder with an infrared gun to see if there is a marked temperature difference. A lean cylinder would be hotter, and a rich one cooler.
 

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god of the sea people
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did you check for a miss? i'd say you may have a bad coil pack, spk plug, etc, and may not notice it at idle... it may be a dumb question, but have you checked? or done a compression test?
 

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Discussion Starter #5
Not a dumb question at all. The engine is dead smooth at idle and the exhaust manifold temps are within a few degrees on all cylinders. I'm going to try swapping plugs first, to see if I have one that's dropping out under load. But you have a good point about the compression test, because it would also show a bad cam lobe. A short lobe would still idle oK, but not do well under load. I'm a pretty good wrench and have built my share of engines, but I'm not completely up on how you'd find and injector that was only spraying 50% - which would sure cause the problem!
 

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god of the sea people
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hptuners can show pulse and flow rates for injectors.. at least injector banks, as in driver/passenger i believe.. if you know a guy who uses that program, hook it up to your car and run around the block. it will log every value for the whole run.. inj pulse, knock retard, o2 voltage, throttle position, a/f ratio etc.... worth a shot.. im pretty sure the 2 inj banks should be equal in both pulse and flow.. if you don't have hptuners handy, i'd suggest pulling the inj. plugs and checking the resistance across each injector. i don't know what the value should be, but if there's one that's different it could indicate a problem....
 

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Discussion Starter #7
I know that it is easy to see the pulse rate and time that the ECU is setting for the injectors and tyring a data logging program may be worthwhile. I have an Autotap system for Ford and I think it is time to buy the GM software/adaptor. My concern is not that the ECU is giving bad commands; I suspect that there is a component, like a plug, injector, cam lobe or port which is not up to spec. The ECU can command a given pulse for an injector, but how do we know that the correct amount of flow is actually occuring? If one cylinder on a bank is lean, the ECU will simply add fuel to the other three to make the whole bank look happy to the O-2 sensor.
 

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god of the sea people
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but it will take time for the ecu to see the lean condition and compensate. you should be able to see it happen, at least with hptuners. i'd have to think it's worth a try.
 
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