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Discussion Starter · #1 · (Edited)
I'm working on the broken exhaust manifolds on a 1996 Impala LT1 (iron heads) this weekend, either welding a nut onto the broken bolts or if that doesn't work, replacing the gasket with something thicker (possibly by doubling up).

I'm trying to fix a suspected vacuum leak where air is entering the system at the exhaust manifold and causing the engine to run rich by throwing off the O2 sensors.

I like to fix things once and be done with them, so what replacement parts / part nos should I put on my shopping list?

I believe I'll need:
  • grade 8 bolts and studs
  • spacers
  • exhaust manifold gaskets (to engine, and to cat?)
  • possibly 2 O2 sensors
I remember before the forum crash some people complained about the new GM grade 8 bolts. Is there a better source?

Unless I have a reason not to, I'll get my parts from the local Kragen / Napa / Autozone, but would make a run to GM or a specialty store if there's a part I should consider.

Edit: just found the archived recommended parts list. Here's what I have so far:


2 x AC Delco AFS 75 (O2) GM Part # 19178930

Not sure which one of these is right:

Exhaust - Manifold Gasket Felpro - Reg Square Fel-1404 $ 18.95
- or Exhaust - Manifold Gasket Felpro - Big Square Fel-1405 $ 18.95
- or Exhaust - Manifold Gasket Felpro - Big "d"-port Fel-1406 $ 18.95
- or Exhaust - Manifold Gasket 93-96 12552469 $ 6.02
- or 12552469 Exhaust manifold gasket set
 

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Definately fix all the bolts. dont double gasket it, it will just blow out. I used the fel pro d-port ones and didnt have a problem with the stock manifolds. the gm bolts were fine too. but you prolly can get em quicker locally. If you do i recommend getting a flange bolt(washer built in). Otherwise i think you have it covered
 

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Agreed - don't double gasket and Felpro is good. You'll have a hard time finding the stud in grade 8 - GM didn't make it. You can make it by buying a long bolt in grade 8 and cutting off the head, then double nut it at the right spot.
 

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If you have 100,000 or more on your Imp, I would go ahead and replace all four O2's with new ones you can pickup through a Local Stealership, or you can get them at a discount from http://www.rockauto.com/catalog/raframecatalog.php then just Google for the Latest Rock Auto Discount Code, if there is one here on the Forum..... Me Personally, I like the Factory AC Delcos/Delphis, and are worth the money, but the Bosches/DENSO/Standards are decent replacements on a Budget....

For Replacement Bolts, I would Recommend ARP's Chromemoly Smallblock Chevy 12-Point Header Bolts(if you can get them to fit)..
Here is their Header Stud Bolts, and they also have Standard Length Header Bolts Available from Summit or any well Stocked Auto Parts Stores...
http://www.summitracing.com/parts/ARP-100-1402/?image=large
 

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Discussion Starter · #5 ·
You can make it by buying a long bolt in grade 8 and cutting off the head, then double nut it at the right spot.
How do I know where to put the double nuts on the chopped bolt?

Also, what length bolts / studs do I need? (Man, I wish I could search the old messages).

From the factory service manual, it looks like the exhaust manifolds are attached with:

Driver's side: 5 bolts, 1 stud, 4 spacers.
Passenger's side: 4 bolts, 2 studs, 4 spacers.
 

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I'm working on the broken exhaust manifolds on a 1996 Impala LT1 (iron heads) this weekend, either welding a nut onto the broken bolts or if that doesn't work, replacing the gasket with something thicker (possibly by doubling up).

I'm trying to fix a suspected vacuum leak where air is entering the system at the exhaust manifold and causing the engine to run rich by throwing off the O2 sensors.

I like to fix things once and be done with them, so what replacement parts / part nos should I put on my shopping list?

I believe I'll need:
  • grade 8 bolts and studs
  • spacers
  • exhaust manifold gaskets (to engine, and to cat?)
  • possibly 2 O2 sensors
I remember before the forum crash some people complained about the new GM grade 8 bolts. Is there a better source?

Unless I have a reason not to, I'll get my parts from the local Kragen / Napa / Autozone, but would make a run to GM or a specialty store if there's a part I should consider.

Edit: just found the archived recommended parts list. Here's what I have so far:


2 x AC Delco AFS 75 (O2) GM Part # 19178930

Not sure which one of these is right:

Exhaust - Manifold Gasket Felpro - Reg Square Fel-1404 $ 18.95
- or Exhaust - Manifold Gasket Felpro - Big Square Fel-1405 $ 18.95
- or Exhaust - Manifold Gasket Felpro - Big "d"-port Fel-1406 $ 18.95
- or Exhaust - Manifold Gasket 93-96 12552469 $ 6.02
- or 12552469 Exhaust manifold gasket set
Zippy I am having the exact same issue. my 94 pala is running crappy and you can hear an audible noise at the manifold when you hit the gas. Been thru the gauntlet of checks. Egr,fuel pressure good.replaced pcv valve FF. cleaned maf. plugs wires good. Cleaned TB. NO CEL either and it just runs like pure s***.How does your car run?
 

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How do I know where to put the double nuts on the chopped bolt?

Also, what length bolts / studs do I need? (Man, I wish I could search the old messages).

From the factory service manual, it looks like the exhaust manifolds are attached with:

Driver's side: 5 bolts, 1 stud, 4 spacers.
Passenger's side: 4 bolts, 2 studs, 4 spacers.
You don't need any stud on the driver side and only 1 on the passenger for the alnernator bracket. Match up and duplicate the old to the new - at least one out of 3 of your old should be complete.
 

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Discussion Starter · #9 · (Edited)
help with pass side exhaust manifold

There's a connector on the passenger side manifold that seems to be holding the manifold in place. I think it's the secondary air connector. I can't figure out how to get at it to disconnect it, and the factory service manual doesn't spell it out.

Any tips?

I've removed all 3 studs connecting to the cat, and I still can't lift the exh manifold out. It's free from the engine, but stuck down b y the cat flange.

Suggestions greatly appreciated.
 

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if you want ac delco 02 sensors, you will have to get them from gm or a online parts seller, az and aa do not carry them
 

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There's a connector on the passenger side manifold that seems to be holding the manifold in place. I think it's the secondarry air connector. I can't figure out how to get at it to disconnect it, and the factory service manual doesn't spell it out.

Any tips?

I've removed all 3 studs connecting to the cat, and I still can't lift the exh manifold out. It's free from the engine, but stuck down b y the cat flange.

Suggestions greatly appreciated.
Yes, that is the EGR tube. I got at it with a box-end wrench from beneath the car two nights ago when I fixed my exhaust leaks.
 

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I broke 4 out of the 6 exhaust manifold bolts tot he down pipe - I drilled them all our - tapped them - chased them and installed new studs
Kit from Napa - 600-3231 - correct nuts and studs
 

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Discussion Starter · #14 ·
The EGR tube was my downfall. I couldn't see or feel a way to get at the bolt from the top or below. But I also didn't take out the oil check tube, which the FSM recommends, and that might have given me more room to get in there.

So I never managed to fully remove the passenger side manifold, but it had enough play for me to replace the gasket on that side.

Here's what I found during the process.

Driver's side manifold had several bolts that were fingertight (!) and one random non-graded bolt in position 1 (front). Replaced all bolts/studs with grade 8 bolts and washers (flanged bolts unavailable). The old gasket was made of three thin layers of metal, and I found signs of exhaust leakage on one of the ports. The new Felpro gasket is thicker and more compressible.

Passenger's side was a nightmare. Bolt/stud 4 completely gone, bolt 6 (rearmost) broken off 1/8" - 1/4" inside the hole. Signs of exhaust leak on two of the ports, including rearmost.

Due to EGR problem above, was unable to get to pos 6 to pull out bolt. Replaced gasket, replaced all bolts and studs with grade 8 (only used one stud on this side for alternator mount).

Except bolt 4. This one part consumed what felt like hours of my and my friend's time. We'd take turns trying to get the bolt in, and never succeeded. Finally he looks at the bolt hole with a mirror and determines that there's a helicoil in there. No wonder!

So today's another trip to the hardware store to find a 1/4" bolt and see if it fits.

With most of the day gone, despite our best intentions, we gave up on doing it right and just put it back together. 2 passenger side bolts are still missing. But with the new gaskets, grade 8 parts, and proper torquing all around, the engine runs without codes and is noticeably quieter. But we'll see how it's doing a week from now.

In the end, we did no harm and made the engine better. But I still want to do a proper job.

Having started this once, Here's my summary. First off, the advice here was great, and made the job much easier.

The driver's side job is a cake walk. If you've never done the exhaust manifolds, do this side on day 1 as practice. Save day 2 for the passenger side.

The passenger's side is more challenging. Harder than replacing an Optispark, in my opinion. Many of the angles are difficult and you'll be working blind. And the EGR (secondary air) tube that runs to the manifold is in a spot I couldn't get to even with the factory service manual open. The manual says where the bolt is, but not how to reach it. Probably my fault for not taking out the oil tube. That EGR bolt is the one part that kept us from properly doing the job.
 
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