Friday, June 24, 2016

3.4L GM Engine: How to replace the lower intake manifold gaskets

     Coolant was present in the oil of my friend's 2003 3.4L Pontiac Aztec. Both the 3.4L and very similar 3.1L have been plagued with leaking lower intake manifold gaskets. This job is not technically difficult, but the sheer volume of components and wiring to remove or re-route make it a frustrating and time consuming repair. In this post I will go into great detail to help someone attempting this job at home. Plan to be without the car for two hard working days minimum. These engines are found in many models of GM vehicles made from 1998 to 2005, such as the Chevrolet Lumina, Malibu, Venture and Monte Carlo; the Pontiac Grand Am, Grand Prix, Montana, Transport and Aztek; the Buick Century and Rendezvous; and the Oldsmobile Alero and Silhouette.

                                                  The job at a glance

  • Tools: a set of 3/8" and 1/4" metric sockets. breaker bar, inch and foot pound torque wrenches pry bar, ramps, shop vac
  • Materials: Oil, coolant, steel wool, 
  • Parts:  Fel-Pro gasket set  MS98003T
  • Cost of parts:  $64.98 
  • Time: 16-20 hrs.

                                      Removal of the upper manifold

1) Drive the front of the vehicle up on ramps or set on jack stands. The wheels stay on.
2) Disconnect the battery.
3) Drain the oil and remove oil filter.
4) Drain the coolant. Open the petcock on the lower left corner of the radiator. 
5) Remove the serpentine belt. This can be done now, or later. 
6) Unwire (13mm) the battery plus lug from the alternator. Then remove the wiring from atop the upper manifold. 
7) Mark and remove all six spark plug wires from the coil assembly. I marked them 1-6 from left to right for accurate and easy re-install. Disconnect the front bank wires from the rear wiring routing and stow the wires (still connected to the front plugs) out of the way.
8) Unplug 10 electrical connectors from the large harness crossing over the left (rear) of the top of the engine. Mark the cables and sockets if desired. I find it desirable. Here is a list of the components, their location in the order I removed them:
       1) Mass Air Flow sensor (MAF): located before the large rubber air inlet duct.
       2) Inlet air temperature sensor: atop the large rubber air inlet duct.
       3) Inlet air control valve (IAC) atop the throttle body
       4) Evaporative canister purge solenoid: Just behind the IAC valve
       5) Throttle position sensor: On the firewall side of the throttle body.
       6) Exhaust gas recirculation valve (EGR) 
       7) Coil assembly wiring harness right side
       8) Alternator control wiring
       9) Coil assembly wiring harness left side       
      10) Upstream Oxygen sensor: on the left side of the coil assy

Now tuck the big harness between the radiator and the front engine mount.

9) Disconnect the cruise and then the throttle cable from the spring loaded winder. Rotate the winder counter-clockwise a half turn and hold it there. The cruise control cable simply unsnaps in a downward direction. Slip the barrel end of the throttle cable out of the slot. 

8) Option: Either unbolt the throttle mounting bracket (three 10mm nuts-the one underneath is very hard to get to until the six inch wide rubber air inlet is removed.) or leave it mounted and squeeze the black plastic spring retainers below where the cables go through the bracket and then pull them through. I opted for the latter. 

Squeeze and release the throttle cable from the mounting bracket

9) Remove the larger vacuum line from the top of the rubber air inlet duct. The other end fits into the rear valve cover and will remain there for now. 

10) Remove the air inlet duct. this is tight squeeze, but it can be is rubber.

11) Remove the evaporative canister purge solenoid valve (remove one 10mm bolt from the upper manifold and then loosen the two upper throttle bracket bolts to allow a little clearance to pull a vacuum line out from under it. Then pull the PCV valve from the front valve cover. Do not disconnect these lines from the valve.. Let them rest out of the way off to the side.

12) Remove the large rubber brake vacuum hose from the plenum.
13) Remove the MAP sensor. This is mounted to a bracket at the mid back of the upper manifold. Remove the two 7mm bolts mounting the MAP to the bracket. Remove the small rubber vacuum hose just under the MAP and also the thin vinyl hose going to the right front corner gas regulator. Remove all as a unit.

14) Unbolt the coil assembly. There are two upper 10mm and two lower 13mm mounting bolts. The lower are best removed from under the car, at least on this Aztek. Then the unit can be pulled up and another wiring connector at the right rear of the unit unplugged. Then pull the whole unit up and out.

15) Remove the other end of the vacuum line that came from the large intake duct.

16) Unbolt the EGR valve from the upper manifold. There are two 10mm bolts holding it in place. A 10mm nut for the transmission dipstick mounts on the right side stud. There is precious little room to get the right side one out. A universal socket adapter works well here. There is a gasket that goes between the EGR and the upper manifold. The EGR will stay in the vicinity, still connected to a small exhaust pipe. 

17) Unbolt the front 15mm alternator bolt. There is a bracket using the left rear upper manifold bolt/stud that provides a nut for that front alternator bolt. This must be removed. Leave the two bolts back by the firewall alone for now. There isn't room to remove the alternator until the upper manifold is removed. 

18) Disconnect the coolant lines that run through the throttle body.  With a 13mm deep well socket remove a nut that holds a bracket to the throttle that is connected to a water pipe that runs to the right of the throttle body. Unclamp these two lines and pull off the rear one. The front one is so short and straight it must be uncoupled when the upper manifold is pulled out toward the front of the engine. A blow dryer works well to swell and soften these rubber lines.

19) Unbolt the five 10mm bolts holding down the upper manifold (intake plenum).  There is a bracket in the middle that held the MAP sensor that will come out with the plenum bolt. There is a 13mm stud/bolt on the left rear corner that contains the nut for the long upper alternator bolt. First remove the nut holding the bracket, then the bracket. On the front left and middle the bolts also mount a wiring harness. 

20) Remove the upper manifold, pulling it off that little coolant hose under the throttle body. 

Removing the lower intake manifold

1) Unbolt the remaining two rear 15mm alternator bolts and remove it over the top of the engine. A box end wrench worked best here. 
2) Remove the alternator bracket. There are four 10mm bolts. One in the back, two on the front of the engine and one for the tensioner.

The alternator mounting bracket is three or four parts in one

3) Disconnect two electrical cables, one in front of the front valve cover for the camshaft position sensor and one above the power steering pump for the fuel injectors, map sensor and coolant temperature sensor.
4)  Remove the three power steering pump bolts using the through holes in the pulley for access. Move the pump to your left as far as possible. DO NOT disconnect the steel lines from the pump.
5) Relieve fuel pressure with a small allen wrench after cap is removed. A bit of fuel will jet out. 

Using a small allen wrench to relieve fuel pressure

6) Remove three 10 mm fuel rail bolts, two on the lower manifold and one on the lines toward the back of the engine.

The 3rd 10mm bolt is on the metal fuel lines to the right

7) Now gently pry up with a screwdriver and remove the rail and injectors from the manifold. They are simply seated in their respective ports. 
8) Disconnect the coolant temperature sensor at the water outlet to allow freedom to set the fuel rail off to the side without disconnecting the fuel lines. 

Lift out and set aside the fuel rail 

9) Remove an 8mm bolt holding the metal coolant line atop the lower manifold. Back up the hose clamp and remove the hose from this tube. 

Now remove another 8mm bolt holding down a coolant union between the rubber hose and the long metal line running in front of the front valve cover.

 This line can now be moved up and forward to allow clearance to remove the valve cover. 

10) Remove the press fit end of the coolant line atop the manifold from the water outlet. this took some prodding and prying and penitrant.

stubborn pipe removal

All components are now out of the way for valve cover and lower intake manifold removal.

11) Remove the front valve cover.  There are four 8mm retentive bolts. The lower two will require socket extension bars. 
12) Remove the rear valve cover.  The stud on the right  for the rear mount of the coil assembly is right in front of the lower right bolt. This necessitated removal of the stud. I had trouble here. The 5.5mm hex end stripped  when I applied too much torque. I had to use a vice grip on the smooth lower portion to turn it off.

13) Remove a coolant pipe leaving the thermostat housing at the rear of the engine. It is held to the lower manifold by a bracket. Push a wiring harness panel-type fastener through a bracket where it blocks access to a 13mm nut. Only loosen this nut to slip the "C" shaped bracket off the stud. 

14) Move the clamp on the upper radiator hose from the end that fits on the pipe to the thermostat housing. Then remove the hose from this pipe.
15) Remove the eight 10mm bolts for the lower manifold. The middle four are longer and easy to remove with a socket and ratchet. The four outer ones are shorter. The two tough ones are under the shelf of each side of the down part of the end air passage. These are harder to reach, particularly the ones on the engine front side. The one on the driver's side can be easily turned off with a wrench, while on the other side there is a limited turn radius. I used a wrench shortened to 3 3/4" to improve the turning radius. 

16) With all of them loose pry up under the right front corner. It broke loose rather easily 
17) Remove the lower manifold.
18) Remove the 12 pushrods. To remove, loosen the 10mm nut on the rocker arms just enough to allow the rods to be removed. Store the pushrods in a box, such as shoebox, in the same position as they were in the engine. They need to go back where they were. 

Make sure to store the pushrods in a box for correct re-assembly

19) Remove the two bad lower manifold gaskets.  

This gasket is compromised in several places

Other maintenance operations easier to do now

    Now it is much easier to do some routine maintenance on this engine, if needed or desired. The Thermostat can be easily be replaced. The rear spark plugs are right in the open for easy replacement.  

Installing the lower manifold 

1) Clean all mating surfaces thoroughly and finish with a solvent such as lacquer thinner. Vacuuming out the ports before reassembly is a good practice. 

2) Place the gaskets in position. They have guides to make seating foolproof.

3) Install the 12 pushrods back into their original position and torque to 168 inch pounds plus 30 degrees. 

4) Lay a 1/4" bead of black RTV in the valley between the two engine banks.

5) Prepare the manifold bolts if not using new. Using new bolts (usually already with sealant) is best. Apply thread sealant to the threads of the old bolts and the the top end of each long bolt. These have some history of allowing coolant seepage.

6) Place the manifold carefully down into place.

7) Install all the bolts in two stages, longer inner ones first. Use a crisscross pattern and torque first to 60 inch pounds and then to 120 inch pounds. Torque the four outer bolts to 18 ft lbs. 

A universal adapter plus an extension works on the under-shelf bolts

 8) Mount the valve covers. Turn the 8mm bolts in finger tight and then torque to 84 in          lbs.                           

                               Installing components on the lower manifold 

        (There are fewer pictures accompanying the install. Please refer back to the j-peg laden disassembly instructions if need on install.) 

1) Install new o-rings on the metal coolant lines. These are included in the Fel Pro kit.

2) Install the coolant pipe back into the water outlet. Tighten down the 13mm nut that holds the bracket for the pipe. A universal adapter helps here. Insert the panel fastener for the wiring back in the hole in the bracket. 

3) Reconnect the upper radiator hose onto the metal pipe. Clamp it back into place.

4) Clean the gasket channels in the valve covers and insert the new gaskets.

5) Install the coolant pipe crossing over the top of the lower manifold. It may be necessary to tap it gently into place with a hammer where it enters the manifold near the water outlet. 

6) Return the rest of the the coolant piping assembly back into position in front of the valve cover. 

7) Mount the coolant union back in the hole near the water pump and turn in the 8mm bolt. 

8) Connect the rubber hose into the coolant crossover piping and seat the clamp. 

9) Turn in the 8mm mounting bolt on the crossover pipe. 

10) Place the power steering pump back into mounting position. It doesn't need to be mounted yet, but the bolts can be started if desired. 

11) Install the fuel rail assembly. First plug in the coolant temperature sensor. Make sure the MAP Sensor wiring is correctly positioned, then position each fuel injector over it's port and gently rock the rail assembly until all are fully seated. Tighten down the the three 10mm mounting bolts.

12) Mount the right lower stand-off for the coil assembly bracket. Use a 5.5mm socket.
       This mounts over the right rear bolt of the rear valve cover. 

13) Plug in the harness that runs over the top of the power steering pump.

14) Plug in the harness that runs along the front of the front valve cover. Install the locking clip in this harness. 

15) Mount the alternator bracket. There are four 15mm bolts of three different lengths. If you got them mixed up, here is some help:

16) Mount the alternator with back bolts only. It is helpful to slip the left rear 15mm bolt into place first as it is nearly impossible, at least on the Aztek I worked on, to put in after the alternator is in place. 

Installing the upper intake assembly and components and finish

1) Clean the mating surfaces of both the upper manifold and the lower manifold

2) Place the two new gaskets in position.

3) Set the upper manifold carefully in place. Make sure to attach the small rubber coolant lines still on the manifold before seating the manifold. Re-attach the clamps and bolt down the 13mm nut holding the bracket attached to the metal coolant lines. 

4) Install the six upper manifold bolts and torque, oppositely and in stages to 18 ft lbs. Most of these do double duty, holding accessories. The right front holds the front spark plug routing bracket; the front right and middle hold a wiring bracket; the middle rear holds the MAP sensor bracket and the left rear holds the front alternator bolt nut bracket.

Here's a reminder of the bracket and accessory positions

5) Install the long front alternator bolt into the bracket that mounts on the left rear corner of the upper manifold. Then install the 13mm nut on the stud and tighten.

6) Install the three 13mm power steering bolts and torque to 25 ft lbs.

7) Install the EGR valve with a 10mm bolt on the left and a 10mm stud/bolt combo on the right. I re-used the gasket, but coated both sides with RTV. This is a tough install due to extremely limited room on the right side. When mounted, make sure to mount the transmission dipstick to the right side stud with a 10mm nut. A universal socket adapter works best in this space. 

8) Install the large rubber intake hose and tighten the two band clamps.

9) Install the tubing into the rear valve cover that goes to the air intake hose. 

10) Install the coil assembly. plug in the connector at the right side.

11) Plug in the rear bank spark plugs into the coil pack.

12) Install the MAP sensor.

13) Connect the brake vacuum hose back into the upper intake manifold.

14) Install the EVAP purge solenoid with the 10mm bolt. It may be necessary to loosen the throttle bracket bolts to reinsert the vinyl line back into the upper manifold. Reinsert the PCV valve into the front valve cover. 

15) Plug the other end of the hard vinyl hose coming form the rear valve cover into the port on top of air intake duct. 

16) Re-install the throttle and cruise cables through the mounting bracket and load into the winder.

17) Snap the large wiring harness back into position in front of the front valve cover. 

18) Route the ten connector wiring harness back into position.

A reminder of  how to dress the large wiring harness

19) Plug in the ten connectors in reverse order of removal. Make sure to route the                 harness into the snap-in holders. 

20) Connect the B+ cable back on to  the alternator lug and secure with the 13mm nut. 
      Snap into the cable router. 

21) Plug the front spark plug wires back into the coil assembly. Snap them into position in       the right rear cable router

22) Install the serpentine belt.

Plenty of components in this belt path

23) Replace the oil filter and fill the crankcase with fresh oil

24) Fill with new coolant. 

25) Reconnect the battery

26) Test drive the vehicle and check for leaks. Nice work. You saved some serious jingle.

                                                                         foot pounds             inch pounds


  1. THANK YOU so much for this, have been following your YouTube series. About ready to take off the lower manifold, you saved my girlfriend's daughter $900, so yeah, serious jingle is right! :D

    1. You're welcome. And credit to you for tackling this tough job. I'm always glad to see my videos and blog get some good use.

  2. I am about to embark on this jurny as my car is giving signs of a bad manifold gasket. I am really glad I found this site cause I need all the help I can get. I have the 3100 series 3 motor but its basically the same thing as this one. I also want to rebuild the tranny but that will be a project for the future. The car has 185k miles and runs great all but when idling. It misses and bucks along with a bad gas smell similar to a vaccume leak but all vaccume lines are fine.

  3. Thanks for sharing the post.. parents are worlds best person in each lives of individual..they need or must succeed to sustain needs of the family.

  4. Please continue this great work and I look forward to more of your awesome blog posts. robot vacuum reviews

  5. Thank you for posting ,about to do this on my 2000 alero

  6. Thanks! This was a huge help in getting the removal steps in the best order. A note to others: be careful when prying up the fuel rails, on my engine an injector retaining clip broke before any injectors pulled out of the manifold. Disengaged the clips first, then popped the rails off the injectors. To remove each injector, pried up gently from the bottom while rocking the injector back and forth. It will slowly work its way out.
    Again, thanks for the massive effort it must be to make these posts/videos...

  7. WARNING: It's not just your intake gaskets!

    I'm the owner of a 94 Camaro with the 3.4 V6 that I just restored. Both the 3.1 and 3.4 have the same type of heads which use the intake manifold to complete the valve cover, gasket surface.

    When you remove the valve covers, you'll notice that the aforementioned surfaces are not equal in height. The intake surface will be lower than that of the head. The reason for this is because the intake bolts go "straight down" into the head, resulting in a "wedge effect" which will drive both heads downward and away from the intake's mating surface over time with expansion and contraction. The intake bolts are not directed at a right angle towards the head's intake surface(as they should be and had been for decades for this very reason).

    When you remove your heads (which you will), remove and take a close look at the four, metal dowels that hold them in place. You'll not only see thread marks within them from the head bolt, you'll see that they are distorted from being sheared between the block and heads. I recommend that you not only replace them, but find some that are beefier to help prevent the problem. The factory dowels are quite thin and must be replaced; along with the head bolts that stretch upon torque and are useless thereafter. Clean your block threads with a tap, too.

    Be sure to check all lifters to make sure none are flat. "KEEP THEM IN THE BLOCK, AS TO PREVENT MIXING THEM UP." I disassembled each of mine, using a bent coat hanger, plyers, and a copper gun cleaner brush to remove the residue within that causes collapse, and a dab of assembly lube on the lobe surface upon reinstalling each one. Upon finishing this task, which assures no collapsed lifters and proper starting height for valve adjustment, tighten the rocker nut while moving the pushrod "up and down" until it just barely can't be moved up and down anymore without depressing the lifter plunger. Don't do the twisting method; that's mindless and stupid. Just find the correct valve to crank position procedure and follow my advice. Also make sure to tighten the rocker nut "one full turn" after removing the aforementioned lash. You'll find that most books say 3/4 to 1 1/2 turns, as if valve clearance bears no relevance, lol. Idiots. I've been working on Chevy's since the 70's, and one full turn has always been the standard... worked for me.

  8. Is the process of taking things off the engine to easier access the intake manifold the same on say a Oldsmobile Alero? This guide is for a pontiac aztec which i assume has a more cramped engine bay so maybe we can skip some steps?

  9. Thank you for your information. But, when I removed the the push rods I miss the position of the pushrods. So, I cannot find the same position as they were in the engine. Do you know how can I find which ones to go back where they were?

    1. I know it's been 4 years since you asked this question but some others may have the same issues. On forward drive 3.1 L and 3.4 L back row starting on passenger side it goes E I E I I E
      Front starting from same place on passengers side E I I E I E

      E= exhaust which should be just a little over 6 in long of a push rod.
      I= intake and those pushrods should be approximately 5 and 3/4 in long. Hope this helps somebody.

  10. Thanks for this kind of help. Soon, I will replace my head gaskets in my 2002 Olds Silhouette and this is a good guide.

    I hope to be a lucky & smart guy! Greeting from Mexico!

  11. This article is very informative for gasket users and gasket manufacturers also.Metal Spiral Wound Gaskets are used with the flanges by oil industries to avoid the leakage of flange joints.

  12. Very helpful, thanx. Ps, do u know where I can buy the 10mm bolt that secures the 2 fuel lines coming from the fuel rail?

  13. Thanks super helpful got a question if still active

  14. I wanted to give you a big thank you for making this video. Without it I would not have tried to fix my 2004 Montana. I followed it to the T with no issues. It's been a year and a half with no problem. Thanks again The Montana is All I had at the time. It was do or die.