The car was perfectly fine before and now it has this odd tendency to heavily vibrate when I let off the gas. Doesn't matter which gear I'm in, doesn't matter at what speed. There is NO vibration during acceleration no at idle and the only way of getting rid of it is to keep my foot on the gas or shift to neutral. The vibration is also present during gear changes.

Motor mounts are fine and the header is not causing the vibration. What gives?

 

sounds like a partially obstructed exhaust, maybe the cat.

 

I've got 500 miles on the full exhaust system and the problem started at 300 miles. Regardless of when I had no cat. and after installing a high flow cat. the problem was still present.

Axles are brand new, new hub bearings, and I don't believe this is suspension related.

The main thing here is it only vibrates when I let off the gas while in a gear - it gets real rough when I completely take my foot off.


Modified by ketchup at 12:34 AM 8/2/2008

 

does the vibration come more from the driver side or passenger side? more from the rear or the front? does it feel like an unbalanced tire or loosened lug nuts? How does the engine sounds during these vibrations? partially obstructed fuel injector or failing fuel injector could cause a weak explosion in 1 cylinder when less gas is pushed through.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Kronn 98SH &raquo;</TD></TR><TR><TD CLASS="quote">does the vibration come more from the driver side or passenger side? more from the rear or the front? does it feel like an unbalanced tire or loosened lug nuts? How does the engine sounds during these vibrations? partially obstructed fuel injector or failing fuel injector could cause a weak explosion in 1 cylinder when less gas is pushed through.</TD></TR></TABLE>

Front drivers side of the car and I'm able to feel the vibrations thru the gas pedal. It feels like the motor is set on [VIBRATE MODE] and just keep rattling. Doesn't sound any different when you downshift - just the echoing in the cabin from the vibrating.

New fuel filter. Also the motor doesn't sound like it has a misfiring cylinder, wouldn't that be present at all times? My idle is fine, acceleration is good, just when I let off that gas it vibrates. This is insane.


Modified by ketchup at 12:47 AM 8/2/2008

 

if the engine doesn't sound any different, i would guess it isn't a firing issue or piston movement issue.... maybe loose motor mount? What happens if you're stationary, in neutral, and you rev the engine then let off the gas? same thing? If so, that should rule out anything suspension-related or transmission-related.

 

I believe it vibrates if I hit the gas and let go in neutral as well. No vibes during any pedal, again only when I let go. Could it be the EGR/vaccum plugged somewhere?

 

Motor mounts possibly or something in the tranny perhaps? A video or sound clip would do wonders maybe?

I noticed you said motor mounts. Have you reved the motor up and down while watching the motor? If so how does the motor shift?

I would say an inbalance somewhere in tranny or motor maybe.

If not, I would than suggest fuel related. What an interesting scenario

 

Yeah your not going to like what I have to say here. But you should check to make sure every bolt is toruqed down there. Not just your mounts, but the brakets that hold the mounts to the motor. Also check out your flywheel too, make sure all teeth are there.

 

yeah i'd put my money on motor mounts as well.

 

yea but if it were the motor mounts, wouldn't it vibrate ALL the time?

Motor doesn't seem to move while I rev it.


Modified by ketchup at 4:36 AM 8/2/2008

 

Well when you rev it motor is in one position. when you down shif or let go of gas in gear motor is in dif position, that's why its posible that it has something to do with mounts, loose or something. or something els, I had simmiler problem but it was hafe way down my exsahust, tuching a plate at 3-4 RPM. Hope this help's
my 1.5 cents

 

I made a video clip while in the car driving around. You can't really tell that the car is vibrating so I'm not going to upload it. I'll try to get one of the engine bay. The motor looks pretty stable under load. I'm gonna re-torque everything down. 90lbs on the motor mounts? What's the TQ Spec on the bolts holding the mounts to the engine/tranny?

Exhaust isn't rubbing on anything, would have a rattling noise if it was?

 

nevermind.


Modified by ketchup at 2:20 AM 8/4/2008

 

balance shaft/belts? maybe too.

any luck yet?

 

Just because it doesnt wobble or shake at high RPMs doesnt rule out its a bad motor mount.

Take for instance you swing a small child around very slowly in circles, he can still move his legs and arms. But you swing him really fast and he is seating in the force of the swing and can only scream .

So when your motor is idleing at .8k rpms, it has room to move around and shake and make all kinds of funny noises cause there is no force holding it in place. Now if you swing that motor up into Vtec, the mounts are all forced into place by the ammount of presure the motor is generating by moving that fast.

Understand

 

haha good analogy

I found a bolt loose while re-torqing all the mounts. The culprit was the driver side mount, one of the bolts from the motor's bracket.

After tightening it all back together, I marked all the bolts so I'd be able to tell if they've come loose from the engines vibrations.

Thanks for the help fellas