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I'm not positive on f-bodies but I know on my vette there is an extra brace that bolts to the exhaust manifold on the passanger side. When I installed my headers I simply eliminated that bracket since it was a PITA to shim it out to work with my headers and I have a slight noticeable vibration with the ac on now.. don't know if this is your problem or not beause I don't know if you have a serp belt setup or a v-belt setup, and I don't know if this would even apply to an f-body, the ones I've owned never had A/C..

 

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Looks like this:

 

I know there was a bracket like that but it ddint run down to there it ran to on top of my manifold, I think they possbily left it off, will check tommarow

 

OK, I checked and the bracket I thouh tey could have left off is there, any other suggestions?

 

what is the engine rpm when it starts to vibrate?

 

Its what its always been at before I got the headers

 

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i meant when the car is vibrating what are the RPMS doing

 

Shop corrected!

 

it sounds to me like the vibration is actually the engine... if you slightly bring the RPMS up to about 750-800 will it go away? mine used to do that when i would use the a/c... the a/c puts quite a bit of strain on the engine at idle...

do you have a 02 sensor? might need to switch to a heated 02

 

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the heated O2 is important do to headers not retaining as much heat as stock manifoulds the exhaust in the header cools and screws with the O2 which is basically a fancy thermometer...

what headers did you have installed?

if this vibration was simply caused by a rubbing header... the car wouldnt have stalled when you tried to bring up the RPMS sounds like the o2 sensor is reading rich/ cooler the ECM is trying to lean it out when you try and open the throttle you only make it worse

 

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the it i assumed was the car... it is very common to need a heated O2 after headers... i think they also suggest one in the installation guides

 

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There's another bracket that supports the A/C compressor that is difficult to re-install with the addition of headers. It is U-shaped and mounts to the forward two exhaust manifold bolts in stock form. With headers a spacer is required to re-attach it and it may need to be trimmed to clear the headers.

Loss of this bracket could easily cause vibration problems when the A/C is on at low rpm. Once it spins up the vibration problem won't be as apparent.

If you think this may be your issue, I can post a photo of the modified bracket on mine.

 

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does it sound like a tin rattle? my guess is it's the heat shield or the cat itself. It had to be moved and jostled around a little bit when putting the headers in. I know many times it's that. it may look fine but when ITS COLD jiggle it and see if that is the source. then have someone start it and and put it to the troublesum rpm and see if that's it.

 

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Attached are two photos. The first shows the bracket on the rear of the compressor and you can see where it had to be trimmed around the headers (it used to mount to two exhaust manifold bolts). The second shows the nut on the stud that is used as a spacer for the bracket. In stock form it mounts to the outside of the manifold which is an inch plus away from the head, not so with the headers.

 

When your AC kicks on, does the idle speed go up? It should to compensate for the added load of the AC. If it doesn't, you could look into why, or you could raise your base idle on the car (first option is better).

 

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You're on an older car so things like the bracket and the location of the compressor are different. I don't see anything that I lill need ot mod.

You may have to purchase a bracket from Headmen depending on what headers you used. You're on an 84 and I have a feeling something isn't right with your A/C and or bracket setup. The instructions I have for my headers indicates an older model compressor reffered to as a long compressor MUST use a special bracket they sell. The other type of compressor like the Vett and I have needs that u-mount cut. I have never seen that u-mount on a F-body though. It's probably because I've only owned TBI cars.


Some cars just shake with the A/C on. I know my aunts Kia did. Felt like the world was ending lol. I would look into the bracket issue.

 

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Alright. Take the belt off the A/C compressor and run it. If it doesn't vibrate you'll know it's the compressor/mounts.

Different idle speeds will produce different vibrations, hence in neutral it stops. Turning can also affect idle when the power steering loads the engine.

 

I keep thinking you have an 84 for some reason.


Follow naf's suggestion.

 

I will do that when I get time and then I will report back here and let you guys know whats up, it may be a little while because I havent had much time to mess with my car.

 

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