I just justified cam swap/dod delete...or at least tuning out afm - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 21 (permalink) Old 11-18-2012, 02:21 PM Thread Starter
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I just justified cam swap/dod delete...or at least tuning out afm

Ok so I am still new here, I've only had my car for about 3 weeks. It's an 08 GT with about 50k miles. I didn't notice it when i bought the car (because I was just excited as hell about the car) or maybe it just started happening, but i get a nasty vibration from about 1100-1350rpm. It has never happened in first or second gear, but right around 40mph on my local roads makes it very noticeable.

At first I figured this was a problem with the balancer. Even when I bought the car I noticed the balancer is plagued with a wobble, as I've seen all over on these boards. I figured no big deal, I'll slap an sfi rated balancer on there and call it a day (which is still the plan).

Well i was out driving today and realized that if I put in in manual mode, theres no vibration in any gears. Guess that rules out the balancer and means its the afm? Hopefully someone here can shed some light on the issue.

I would not mind doing a cam swap, and actually look forward to it, but I can't fund it right now.

I guess my question is- do you guys think it is in fact a problem with the afm, and do you think its doing any damage as it runs this way?

I know its hard to diagnose anyone else's problems through a computer, but any info would be appreciated!
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post #2 of 21 (permalink) Old 11-18-2012, 02:27 PM
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This is normal. You'll feel a slight vibration when the AFM kicks in, AFM does not engage in manual mode.


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post #3 of 21 (permalink) Old 11-18-2012, 02:34 PM Thread Starter
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I guess i could have explained a little better. Lets say I'm cruising at 40mph, if I keep my rpm between 1100 to about 1350, I will have a steady vibration that does not go away until I give more throttle and exit that rpm range. The vibration is even noticeable to the girlfriend (who doesn't know jack **** about cars).
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post #4 of 21 (permalink) Old 11-18-2012, 02:35 PM
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Have them replace the motor mounts with the newer ones

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post #5 of 21 (permalink) Old 11-18-2012, 03:11 PM
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AFM does give an abnormal amount of vibratation as 768mph said. I noticed it on my car when cruising too.

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post #6 of 21 (permalink) Old 11-18-2012, 03:45 PM Thread Starter
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Originally Posted by PSMG8GT View Post
Have them replace the motor mounts with the newer ones
I have read a few guys complaining about the old mounts. I don't think that is the problem in this case (could be wrong) but it sure couldn't hurt. Anything I should tell them to make them cooperate and do the swap?
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post #7 of 21 (permalink) Old 11-18-2012, 08:31 PM
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Definitely the motor mounts. That's the first thing I had replaced under warranty after I bought the car. The updated mounts eliminated 80% of the vibration. You can still tell when it kicks in, but much less noticeable. AFM will always cause vibration as it changes the balance of the engine. The updated mounts are designed to absorb more of it.


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post #8 of 21 (permalink) Old 11-19-2012, 04:55 AM
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I thought the TSB on this issue stated that the dealer should replace the Transmission mount, not the motor mounts. I had the same issue....vibration and then a moaning sound....and the new tranny mount cured it.

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post #9 of 21 (permalink) Old 11-19-2012, 06:31 AM Thread Starter
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Definitely the motor mounts. That's the first thing I had replaced under warranty after I bought the car. The updated mounts eliminated 80% of the vibration. You can still tell when it kicks in, but much less noticeable. AFM will always cause vibration as it changes the balance of the engine. The updated mounts are designed to absorb more of it.



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Wow ok, good info. Thanks! Was it hard convincing them to swap mounts?
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post #10 of 21 (permalink) Old 11-19-2012, 06:34 AM Thread Starter
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I thought the TSB on this issue stated that the dealer should replace the Transmission mount, not the motor mounts. I had the same issue....vibration and then a moaning sound....and the new tranny mount cured it.
Thanks! Good info, and I guess it couldn't hurt to have the motor and tranny mounts swapped! Only a few months left on the 5 year, so better now then later!

I guess you guys have successfully disproved my AFM theory......

I still want a bigger cam though!
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post #11 of 21 (permalink) Old 11-19-2012, 12:28 PM
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Do the motor mounts. You can use the engineering mode to see when the AFM is operating when using normal mode.

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post #12 of 21 (permalink) Old 11-19-2012, 01:28 PM
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Originally Posted by Dfarnese518 View Post
Wow ok, good info. Thanks! Was it hard convincing them to swap mounts?
Not too bad. With any vibration they are gonna try and tell you to do a road force balance on the tires. Just be persistent and explain what is going on. Best way to tell for sure is to drive in sports mode until the vibration starts(make sure it's in 6th gear), then tap the shifter up to engage manual mode. There will be no gear change since your already in 6th, so the only thing that changes is AFM will be disabled. If the vibration stops then you have found the issue. Explain to them what you did and the results and they should fix it. Good luck!
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post #13 of 21 (permalink) Old 11-19-2012, 03:08 PM
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Thanks for that information, Joe’sFastG8. As I’ve told many members, I’m not a technician by any means and you helped me to understand the vibration from the AFM more.

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post #14 of 21 (permalink) Old 11-19-2012, 04:04 PM
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I guess you guys have successfully disproved my AFM theory......
I wasn't trying to disprove, I actually agree with you that the AFM is causing the vibration, but there is no way to eliminate the root cause without disabling or deleting it. The updated motor mounts simply absorb more of the vibration so not so much makes it into the cabin.
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post #15 of 21 (permalink) Old 11-19-2012, 04:35 PM
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Just to clarify as I think there is some misunderstanding now that I read through the thread again. The updated motor mounts ARE the fix for excessive AFM vibration. You can't eliminate the cause of the vibration, that is normal, you can only make it less noticeable.
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post #16 of 21 (permalink) Old 11-19-2012, 06:11 PM Thread Starter
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Thanks again joe, and I did understand what you meant. It makes perfect sense. Guess I need to get her to the dealer!
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post #17 of 21 (permalink) Old 11-19-2012, 06:24 PM
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Thanks again joe, and I did understand what you meant. It makes perfect sense. Guess I need to get her to the dealer!
Glad to help! Like I said I had the same issue and the first thing they pointed out was the aftermarket wheels and wanted to do a road force balance. That's when I explained that it stops immediately when switching to manual mode(without a gear change) which disables AFM and showed them the TSB for it. I told them I was positive it was from the AFM. They agreed and ordered the mounts. Maybe bring a copy of the TSB with you just in case.
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post #18 of 21 (permalink) Old 11-19-2012, 06:39 PM Thread Starter
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Glad to help! Like I said I had the same issue and the first thing they pointed out was the aftermarket wheels and wanted to do a road force balance. That's when I explained that it stops immediately when switching to manual mode(without a gear change) which disables AFM and showed them the TSB for it. I told them I was positive it was from the AFM. They agreed and ordered the mounts. Maybe bring a copy of the TSB with you just in case.
Yeah I actually already printed it out haha! My tires are pretty worn, so I expect to hear that as the diagnosis, but I think going in armed with all this info, I'll do just fine.

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post #19 of 21 (permalink) Old 11-20-2012, 11:39 AM Thread Starter
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Alright so she goes to the dealer Friday. The guy I talked to seemed to understand my problem and told me to just bring it in and they'll take care of it. Seemed pretty simple, so we'll see what happens.
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post #20 of 21 (permalink) Old 01-13-2013, 07:17 PM Thread Starter
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Just as an update I did finally get the motor mounts done! After brining my car in for the first appointment, they confirmed my problem was the motor mounts and agreed to fix them. They ordered the parts and told me they'd call me in a few days once they were in. Well the holidays came and I couldn't get my car over there, but I finally made it and the job is done.

The new mounts absolutely dampen the vibration better, now the AFM can only be felt in the gas pedal.

Thanks to the guys at Granite run Buick and GMC!

She is parked for the winter now, but come spring time, the next step is long tube headers, CAI and tune. Cam within the next year hopefully!
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