shaking at high engine speed


3rdChevynow
11-29-2005, 02:31 AM
Hi guys,
First-time poster, reader of this site for some weeks now. Got useful info for fixing problems of my 2001 9C3 impala with a 3.8 engine and 89000 km on it: ISS lubed (steering noise gone) and the cat replaced (acceleration improved a little).
However, a difficult problem: the engine bursts/shakes loudely with a countable frequency, when the pedal is pushed hard toward bottom, in driving or parking. For this: spark plugs changed, air/fuel filters changed, and wires checked, no fixes. When the cat was changed 3 weeks ago, GM technician detected some exhaust leak in the rear exhaust manifold. I made replaced the rear exhaust gasket by a third-party shop (to save money, maybe a mistake: not sure whether the job was well done). The mechanics who changed my spark plugs suggested to do a fuel injection cleaning. Looking at the wear of the original plugs which still are in perfect condition , I do not think that the combusted dirt is the problem.

My question: could the shaking be related to an unsolved exhaust leaking and/or to a possible vacuum leaking at the air intake?

Thanks in advance for suggestions

James

bigrod118
11-29-2005, 06:08 PM
could be the motor mounts, I believe that some 9C? owners found the same problem and it was the motor mount bushings.

park your car on a level surface and pop the hood and try to push your motor back and forth, if it moves a lot, its the motor mount bushings. or at least it should be.

bermis519
11-29-2005, 10:30 PM
could be the motor mounts, I believe that some 9C? owners found the same problem and it was the motor mount bushings.

park your car on a level surface and pop the hood and try to push your motor back and forth, if it moves a lot, its the motor mount bushings. or at least it should be.

You don't physically move the motor, the goal of the test is so rock the car back and forth with it shut off and in park, with the hood open and with the car rocking back and forth, you might see the motor physically move back and forth with the rocking forwards and backwards of the car. If the motor moves then I would suggest getting the motor mounts examined.

Not to be a smart ass, just clarifying what he ment to say...

mike

bigrod118
11-29-2005, 10:31 PM
thank you, I remember reading about it earlier but I couldnt quite remember exactly what others did.

I was close tho. but yeah, do what bremis says.

3rdChevynow
11-29-2005, 11:27 PM
thank you, I remember reading about it earlier but I couldnt quite remember exactly what others did.

I was close tho. but yeah, do what bremis says.

Thank both of you very much for the quick responses, Bigrod and Mike. Very refleshing point, totally beyoud my imagination.

Yha, I tried to push the car, the motor move clearly, judge from the two front torque strut mounts, but not a lot. I can also hear a clicking sound from the lower back of the engine. This click sound can frequently be heard during normal driving, when accelerating or deccelerating. I ignored it because people on this site said it could not be dangerous.

However, I still have difficulty to relate this engine movement to an abnormal engine output. At higher engine vibration, a certain sensor could send wrong signals to the PCM?

I will get the monts checked. Can Anyone gives an approximate estimation for the replacement of the lower motor munts?

Thanks again.

James

One can never learn enough

bigrod118
11-30-2005, 04:03 PM
well unless the mounts and brakets themselves are bent or damaged, they shouldnt need repalceing, what you would have to replace is the bushings. I nkow they sell polyurathane ones for the top, but im not sure about the bottom, you might want to look around, polyurathane is much better than the stock rubber ones. but heres a link to the top ones.

I suppose they do call them motor mounts, but they really are only the bushings.

http://www.3800performance.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MSP-MM-TBv2&Category_Code=EC&Product_Count=0

3rdChevynow
11-30-2005, 10:07 PM
Great info, Bigrod. I appreciate it very much.

Today, I brought the car to a shop. The nice shop manager has apparently no experience in dealing the problem and doubted the motor-mounts' involvement. His inquiry call to our local GM dealer got a firm "Never" response regarding the mounts problem. After seeing the reproduced engine shaking, he stated that it is a normal reaction of the programed engine protection.

I am wondering how high the engine speed and what other signals could trigger the protective reaction.

Considering the facts that the enigine movement is still maginal and the car is still drivable (with a gentle acceleration, though), I might need just to keep in mind of this problem for the moment and to focus first on other more urgent issues, such as a possible air leak of the plastic intake manifold. The plastic surface contacting the throttle body is obviously curved, a visble heat effect. The part around the EGR pipe could be worse. I will replace it with a new and better one.

I will replace the upper bushings by myself and keep the expenssive replacement of lower bushings as the last resort. I will keep you informed.

Later.

James

bigrod118
11-30-2005, 10:15 PM
well I just thougth of it today, but what kind of shop did you take it to. I take it a mechanical fix my car type one. you might want to swing by a firestone or tire shop and have them check the cv joints and the suspension in general.

3rdChevynow
12-01-2005, 02:03 AM
well I just thougth of it today, but what kind of shop did you take it to. I take it a mechanical fix my car type one. you might want to swing by a firestone or tire shop and have them check the cv joints and the suspension in general.

I dropped to a local mechanical shop around my work place.

I will make checked the cv-joints by a speciallist. The suspension had been checked for the under-hood clicking sounds. They suspected the strut catchadges and wanted to take them out just for an examination. I do not believe it, because the noise is not car-movement related, but engine-engagement related.

By the way, I have already ordered the stronger upper bushings you have passed on the link for. It seems to be one of least expenssive ways to get the problem. I need to fix the anoyant noise anyway.

Thanks again

james

MCO_Death
12-03-2005, 01:34 AM
Does the car do this engine shaking while your in Neutral / Park? Or always while phsycially driving around.

bermis519
12-03-2005, 01:41 AM
I think the clicking sound your hearing might either be, just the sound of the transmission internals moving from the weight shifts back and forth, and for you other guys. what are the signs symptoms of the engine cradle with bad welds, I remember reading awhile ago about those welds, also the clicking could be the CV joints.

I had a back shaking in my impala and i could never figure out what it was, i had both lower control arms replaced, the tie rods replaced, both of the parts were bad, but low and behold, the damn shake was still there, so i got new tires..still there, moved the tires around thinking it might be a bent rim, still there, so i just gave up and then got rid of it a month ago!!

Mike

3rdChevynow
12-03-2005, 03:31 AM
Does the car do this engine shaking while your in Neutral / Park? Or always while phsycially driving around.

One time was on the highway ramp, during acceleration. The car was such shaked as if the passenger door was not well closed. After a while, the shake disappeared without any interventions. Mostly, the less violent shake occured in an uphill driving, together with the struggling engine sounds and a special, brief come-and-go electronic-sound-alike hissing (transmission sound?).

When the car is in park with engine running, the pushing of the gas pedal toward the botom can always cause the engine and car body shaking.

A good news is that the load-related sound/shaking have been greatly reduced after I have applied some sealing grease to the ends of the vacuum hose connecting the airbox and the throttle body. I also applied liquid gasket to the warped plastic intake manifold contacting the throttle body. I need to confirm this result with a replacement of the whole upper intake manifold.

I am interested in getting a ODB II scan tool (a ProScan kit for $100 on ebay). It should be very useful to pinpoint the problem by myself.

Good night

James

3rdChevynow
12-03-2005, 04:14 AM
I think the clicking sound your hearing might either be, just the sound of the transmission internals moving from the weight shifts back and forth, and for you other guys. what are the signs symptoms of the engine cradle with bad welds, I remember reading awhile ago about those welds, also the clicking could be the CV joints.

I had a back shaking in my impala and i could never figure out what it was, i had both lower control arms replaced, the tie rods replaced, both of the parts were bad, but low and behold, the damn shake was still there, so i got new tires..still there, moved the tires around thinking it might be a bent rim, still there, so i just gave up and then got rid of it a month ago!!

Mike

Great inputs again, Mike.

Someone in another site said that if a mount problem is not fixed in time, it could ruin the transmission. That scares me. I want to get the click sound now.

The dealer's shop had spent two hours x 3 persons trying to get the click sound source. They concluded nothing but a vague blame of the engine mounts. Since the mounts were not covered by their limited warranty and they seem to know little about the recent GM cars, I just walked away.

If the mounts are a cause, a strenthened upper bushing pair could help to reduce the clicking sound. Then I will process to change the lower ones. I have a pair of performance upper bushing on the way.

Just curious, the replacement of your sold Impala's lower control arms did not cost you a forture, I hope.

The domistic vehicles have more problems, it is true. However, usually the fixing is simple and relatively inexpenssive. Its huge price advantage for owbing the car might pay off all of the repairing and the headachs. If you like to fix things, the headach for others could become enjoyment for you.

Have a nice weekend.

James

billyo69
12-03-2005, 09:12 PM
can you tell if the shaking is in the steering wheel or whole car?And does it get worse when you are on the throttle heavy.And does it go away when you let off the gas.At 80 mph put the car in nuetral and see if it changes things.

3rdChevynow
12-04-2005, 11:15 AM
can you tell if the shaking is in the steering wheel or whole car?And does it get worse when you are on the throttle heavy.And does it go away when you let off the gas.At 80 mph put the car in nuetral and see if it changes things.

Whole car while accelerating, gone after letting off the gas
Now the road shaking has gone after sealing the vacuum leak around the throttle budy.
Thanks for the testing trick.
James

3rdChevynow
12-27-2005, 11:37 PM
well unless the mounts and brakets themselves are bent or damaged, they shouldnt need repalceing, what you would have to replace is the bushings. I nkow they sell polyurathane ones for the top, but im not sure about the bottom, you might want to look around, polyurathane is much better than the stock rubber ones. but heres a link to the top ones.

I suppose they do call them motor mounts, but they really are only the bushings.

http://www.3800performance.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MSP-MM-TBv2&Category_Code=EC&Product_Count=0

An update,

The engine shaking at high speed has completely disappeared after I had replaced the front upper bushings with the performance ones that fix well the enigine movement. Also, the strange transient electronic sound during acceralation has disappeard. It was well the engine mounts that cause the problems, combining apparently with other issues such as vacuum leaks.

The engine noise became somehow louder during acceleration, maybe because of an unbalanced vibration between the new upper bushings and the unchanged lower mounts whose clicking sounds can still be clearly heard time to time. That is another problem to fixe in the near future.

By the way I have replaced the Dexcool with the Prestone extended-life coolant. Next driveway-project will be the replacement of the intake plenum and the EGR pipe tail on the lower intake manifold.

Thank you again for your inputs, guys.

James

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