95 Firebird Formula Exhaust Manifold

Tiny
FIREDUCK
  • MEMBER
  • 1995 PONTIAC FIREBIRD
I have a 1995 Firebird Formula, V8, 5.7L, 6 speed, 110,000 kms. Just had the right side exhaust manifold replaced because it was 'broke" I was told.

Now my car runs worse than it did before! The entire car shakes, there's a low roar/rumbling sound throughout which causes all kinds of buzzing and rattles to dash, etc. and it feels like it's running in "bow low" gear....like a tank. And it just didn't have the same power as before. The engine seems to be running fine, it's not stalling or anything like that. I can hear a noise tho, faint ticking & sound of air. Hard to explain.

Commuter error code only showed faulty ERG value so replaced that as well as a sensor.(don't know what sensor tho). Has a bit more power but still shakes.

My Mechanic says he doesn't know what it could be. To install the manifold the motor mounts were taken off and motor had to be propped up. (pretty tight quarters under the hood!)

I think something got damaged when the motor was propped up. Mechanic says no.

Then he tells me he couldn't get the "right size manifold" for my car anymore, and that the one he got has the same size bolt pattern but it's also "only" 16th of an inch difference in size(smaller) but he said that shouldn't make any difference. (I'm not a mechanic and "just" a girl :-)) so I'm guessing this means a difference in size where the exhaust flows thru.

So I think that between perhaps something getting damaged when motor was propped up AND/OR the fact that the manifold is 16th inch smaller is why I having these troubles.

Seems to me that even 16th inch size difference on a part for a high performance car is the wrong thing to do.

Can anyone explain why it is doing this?

Thanks!


http://www.2carpros.com/forum/automotive_pictures/115431_Pontiac_Firebird_2.jpg

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Friday, November 9th, 2007 AT 2:30 PM

4 Replies

Tiny
BLACKOP555
  • EXPERT
First, nice car

second, check the motor mounts they may not be tight.

When he proped up the engine did he disconnect the tranny or did he jus pull it up? If so he could have damaged that causing it to sound like its running in "bow low".
Also 1/16 is quite the difference. Make sure all the o2 sensors are hooked back up properly also.
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Friday, November 9th, 2007 AT 8:23 PM
Tiny
FIREDUCK
  • MEMBER
Thanks for your reply blackop555. And thanks, it is a nice car. And it ticks me off when it doesn't run right!

Actually, I'm getting the motor mounts changed next week. Mechanic said that could be causing the shaking. However, the car didn't shake BEFORE the manifold was replaced. You'd think that if the mounts were loose, it would have been shaking all along.

Not sure if they disconnected the tranny or not, but that's why I think they damaged something when they propped up the motor. Not very much room under the hood to prop anything without hitting something.

If the O2 sensors weren't hooked back up properly, wouldn't that have shown up when we checked the computer? How many O2 sensors do I have anyway? The only error code we got was for the ERG valve.

But get this. Yesterday the "service engine' light came on. I checked under the hood but couldn't see anything wrong, other then the fan running non-stop. Was not over heating, oil pressure was fine, and didn't notice the engine missing or anything.

Turned engine off and light went out and has not come back on. Called mechanic, he said the error code would be stored and he'd check when I take car in next week.

Here's the kicker. The car runs better now! Not great by any means, it still shakes and engine still sounds like a ticking 4 cylinder, but I can notice/feel a difference.

Things that make you go "hmmm".

Any comments to that?

Also, if the 16th of an inch size difference in the manifold is alot, should I be insisting that it be replaced with the proper sized one? Could that be the sole reason for the cars poor performance?

:-)
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Tuesday, November 13th, 2007 AT 2:03 PM
Tiny
BLACKOP555
  • EXPERT
Well when he unproped it, it probably wasnt set back right on the mounts.

It should show the o2 sesnors when it was hooked, but then again it might not have.

If these do not help with the problem demand he puts a proper size exhaust manifold on!
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Wednesday, November 14th, 2007 AT 7:02 AM
Tiny
FIREDUCK
  • MEMBER
FIRST UPDATE:

I've been asking alot of people questions on my car problem. Was told that perhaps a plug wire could have gotten pinched after motor propped up and then put back. Or maybe the wire has a small cut in it and is arking. So, will have that checked out. Along with suggestions blackop555 made.

And, to heck with changing the motor mounts. One costs $221 the other $216 ! (Canadian $ from GM) They don't make after market ones for my car. Figures. I'm not spending that kind of money. And I don't think that's my problem anyway.I know my car and it doesn't FEEL like loose motor mounts. It FEELS like it's not running properly.

Car goes to the mechanic on Monday 19th.I'll let you know what we find out.

Cheers!
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Friday, November 16th, 2007 AT 2:53 PM

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