Tech-Tip - V6 Exhaust
by Ron Dittmer - Revised February 2002
The Fiero 2.8 liter V6 engine is prone to developing exhaust manifold
problems due to cracks, failed gaskets, and loose or broken bolts.
The function of the exhaust manifolds is to tie the engine to the exhaust
system, specifically the engine heads to the cross-over or "Y" pipe.
There is one manifold on each side of the engine, mounted just below the spark
plugs. Each manifold has three branches, or "Ports" as they are named,
which mate to the engine head, and one main exit tube which bolts to the
"Y" pipe. Each engine cylinder has one dedicated port, totaling six.
A common symptom for a problem manifold can be a loud engine exhaust sound,
similar to a bad muffler. Another symptom can be described as a ticking sound
from the engine. This sound can give you the impression the engine itself has an
internal problem, such as a noisy valve. In reality, the engine is fine, but the
exhaust leak at a manifold causes the engine to "tick".
The first thing to do is to investigate if your V6 Fiero had all Pontiac recalls
performed. One recall involved the replacement or servicing (pending the year)
of the "Under The Rear Window" manifold along with it's gasket, bolts,
and related. General Motors is obligated to perform the recall only once per
vehicle, at their expense. Pontiac does not keep records of vehicles over 10
years of age, so you must research yourself, if the car had the manifold recall
performed. Detailed information about this recall can be found on the internet
by searching for "88-C-24". Some web sites have excellent diagrams.
NIFE may have this data available soon on their website. If your V6 Fiero had
the "manifold" recall performed, the problem is yours alone.
Unfortunately, there is no easy or reliable method for inspecting the manifolds
for cracks and gaskets for leaks, without dismounting them from the engine. Auto
supply stores sell small telescoping-handle mirrors for a few dollars, which are
useful in checking for missing or broken manifold bolts. It is advisable to
first assure all mounting bolts are present, then tighten them adequately to see
if your symptoms go away. If you still have symptoms after tightening the bolts,
then remove the manifolds for a complete inspection.
In preparation for manifold removal, driving the rear wheels up on car ramps
provide a good work environment, much better than jack stands, both in height
and working area. Large thick cardboard is a great help in comfort and makes for
easy sliding in and out. Once the car is propped up safely, disconnect and
remove the battery.
The "Trunk Side" manifold is the easier of the two for obvious
reasons. I prefer to access the six bolts from below. A socket wrench and a box
wrench are the tools of choice. Also inspect the two bolts to the "Y"
The "Under The Rear Window" manifold is quite a challenge to do
anything with. Access from below is the lesser of the two evils. Removing the
exhaust system, specifically the catalytic converter, makes a big difference.
But if you have long and relatively thin arms, you can manage with it in place
with some grief. To further improve access, remove the large relatively flat
heat shield by the cat.
Pontiac's procedure for easier access is to dismount the a/c compressor
assembly, then remove the two front engine cradle mounting bolts, leaving
everything else connected. Then lower that end a maximum of six inches. An auto
shop vehicle lift and tall jack stands are at their disposal. Doing that at home
would require some ingenuity.
Next, remove the round heat shield which surrounds the manifold. This shield is
mounted on manifold bolt studs, using flimsy stamped nuts, which are difficult
to remove with a socket because of their low profile. Find suitable replacement
metric nuts and lock washers at your local hardware store.
If you have air conditioning, access to two manifold bolts by the compressor are
achieved by first removing the lower steel a/c bracket. Then dismount the upper
alloy a/c bracket and compressor together from the engine. Do not detach the
compressor from the upper bracket. Three bracket mounting bolts are accessed
near the battery, requiring the battery removal. Once the a/c bracket is
dismounted, rest the compressor and bracket assembly on the engine cradle,
keeping the Freon sealed within.
A side note... During a/c assembly, if you experience difficulty in reassembling
the upper a/c bracket to the engine, loosen the one big bolt that holds the two
pieces of the dog bone bracket. This will allow for self-centering action for
the a/c bracket mounting bolts to lead in the threaded holes properly.
You will need to remove the oil dip stick to remove the "Rocker Cover Oil
Deflector". Simply remove the one mounting screw and pull out the dipstick
housing using some force. Don't skip this step, as you will want to clean these
manifold mating surfaces for a good seal. If the Oil Deflector is in poor
condition, compromising the seal, you will need to find a replacement.
Unfortunately, the only way to order a new one is through buying the recall kit
described further in this article. Finding a good used deflector can be a
challenge, as they are often in poor shape.
Once you have removed the manifolds, look closely for cracks and failed welds.
It is possible to weld the problem areas back into usable condition. There is a
definite procedure on welding. These manifolds MUST be mounted to something flat
and solid during the welding and cooling process. It is preferred to bolt it to
an old engine head or steel block. If you don't fixture the manifold adequately,
it will twist during the welding and cooling processes, preventing the manifold
from mounting flush against the engine head.
If welding is required from the stainless pipe to one of the rusty steel
flanges, it is best to strip the rust for a good weld. I have used a few
different rust removing products like CLR and Muriatic Acid. All can be found in
home improvement centers and hardware stores. You need to be more careful using
the acid, but it works extremely quick and at about 10% the cost kitchen
products like CLR and Lime Away.
Because of the labor involved, I recommend replacing the gaskets with new,
regardless of condition. You'll not want to do this again. You MUST replace the
gaskets with the high performance variety for use with the Fiero's high output
engine. The industry sells both standard and performance gaskets for GM 2.8
liter engines. The standard gasket will fail prematurely. The performance gasket
has much more impregnated metal than the standard version. The high performance
gasket pair sells for under $30.00, compared to the standard ones for under
$10.00. Specifying the V6 Fiero engine should get you the proper gasket set.
Always replace all bolts with new ones when replacing the gaskets. Manifold bolt
selection is critical. Considering both manifolds, you will need nine bolts, GM
part number 11509843, and three bolt/studs, GM part number 373928. If you buy
"off the shelf" bolts, the "hardness" code number on the
head of the bolts should be a minimum of 9.8 like the factory originals, as a
lower number is a softer material which will encourage bolt stretching,
eventually breaking or loosening the bolt over time. It is also easier to twist
off a softer metal head during installation, as well as breaking a stubborn bolt
during disassembly. A lower rated bolt also rusts more aggressively. Standard
stainless bolts are extremely soft, a poor choice. The "Y" pipe bolts
can be purchased at a hardware store, with the same rules applied.
As previously mentioned, three of the 6 bolts that mount the "Under The
Rear Window" manifold are Pontiac specific studded bolts which provide
mounting points for the encompassing heat shield. You can use generic metric
nuts and lock washers to mount the heat shield to the studs, as their hardness
rating is not critical given their purpose.
If you don't feel comfortable repairing a manifold and want to purchase new
ones, consider ordering the "Manifold Recall Kit" GM #10154785, which
supplies the "Under The Rear Window" manifold, mounting hardware,
gasket, oil deflector and many PCV system parts. As of 10/2001, the cost of the
kit listed at $240, much less than buying everything individually. Some dealers
will negotiate a better price. GM #10154787 listed at $101, which is everything
except the manifold itself. The "Trunk Side" manifold is different, so
don't order two recall kits.
If you break a bolt during removal, or if you find that you have broken bolts,
there are some tools available that will be helpful in removing the left-over
stud. I do not have personal experience with these specific tools but I was
told, three parts can be ordered from Kentmore tools at 1-800-345-2233. Drill
bushing #J38782-1 around $10, Drill fixture #J38782-2 around $9, and screw
extractor #J38782-4 around $6. Total around $26 plus UPS. You will also need
three hold down bolts, M8x1.25x40mm, and a "best you can buy" 5/32
drill bit. If the broken bolt is at the #2 cylinder, you will probably need a
right hand drill attachment.
During assembly, apply anti-seize compound to the threads of all bolts to
prevent future "rusted-in" condition.
At every oil change, inspect the tightness of the bolts, as they often become
loose. The ones most prone are the mounting bolts for the ports closest to the
"Y" pipe. This is probably due to the extra stress on them from the
engine-to-Y pipe movement. Fortunately those bolts are easily accessed from
below. Given, most manifold cracks form near the "Y" pipe, I suspect
loose bolts introduce excessive stress on the manifold, causing the cracks to
If you plan to hire a mechanic to do this job for you, perform your own
inspection in advance of the 12 mounting bolts, 6 per manifold. Brief your
mechanic in on your findings, and emphasis your concern over any missing or
broken bolts. This will help insure he addresses every mounting point.
Doing this job myself three times on three different Fiero-GTs, I have to say it
is a dreaded project. I have always had other cars to use during the down time.
The key to a speedy process is to buy all new gaskets, bolts, studs, nuts, and
lock washers, in advance. A cracked manifold will add to the down time, unless
you have fast convenient access to a welder, or have replacement manifolds on
I did one other process for all three Fieros, when servicing the exhaust
manifolds. That was porting them for an estimated 8 horsepower increase. See