Changing the Spark Plugs on a Mitsubishi 3000GT or Dodge Stealth

Changing the Spark Plugs on a
Mitsubishi 3000GT or Dodge Stealth

These instructions apply to 1995 NA and TT DOHC Mitsubishi 3000GTs, but are easily transferable to any model/year or 3000GT or Dodge Stealth.

Also note that these instructions involve removing the plenum and throttle body; if you only want to change the plugs (not check compression), it is possible to change the plugs without completely removing the plenum.

The Procedure


Remove Center Cover from Front Bank Valve cover
  Front Center Valve Cover
  This plastic plate is held in by the 8 bolts at its edges and covers the front spark plug wires/wells. Use either a large Phillips screwdriver or a 10mm socket. Picture shown with plate removed.


Remove the Accelerator Cable Bracket
  Removing the Accelerator Cable Bracket
  Two 10mm bolts (5 N*m) hold the accelerator cable to the rear of the intake plenum. Remove the bolts and pull the bracket away from the plenum. Leave the accelerator cable attached to the throttle body. Note when reinstalling the bracket, adjust the bracket position so that there is minimal play in the cable, but be sure that the throttle plate is completely closed when you are not pulling on the cable! You can also check out the Throttle Cable Adjustment page for more information.

Non-Turbo shown above; Turbo shown below.


Remove Rear Turbo Compressor Outlet Pipe [Turbo Models Only]
  There is a single 12mm bolt that holds the black outlet pipe to the compressor housing. Remove the bolt. There is also a 12mm bolt that secures the pipe to the plenum. It's about halfway down the pipe on top of the plenum - remove this bolt, too. Finally, you need to loosen the hose clamp on the hose that attaches to the other end of the pipe. At this point, the pipe is free and you should be able to remove it.


Remove Wiring Harnesses from Left Side of Intake Plenum
  Removing the Wiring Harness
  Two 10mm bolts hold the bracket to the left side of the intake plenum. Remove the bolts and push the connectors away from the plenum. It is not necessary to unplug the connectors. Note that the OEM FWD (Non-Turbo) setup is shown on the left and the Turbo setup (with ek2Development cover plate) is shown on the right.


Remove the Front Wiring Harness Rail
  Removing the Wiring Rail
  Two 10mm bolts hold the wiring rail to the front of the intake plenum. Remove the bolts and pull the rail away from the plenum. Again, note that the OEM FWD (Non-Turbo) setup is shown on the left and the OEM Turbo setup is shown on the right.


Disconnect Clutch Booster Vacuum Hose [Turbo Models Only]
  Remove the clamp by pinching it and sliding it off of the hose. Then the pull the hose off of the nipple on the plenum.


Disconnect the PCV Hose [Non-Turbo Only]
  Disconnecting the PCV Hose
  Remove the Positive Crankcase Ventilation (PCV) Hose from the intake pipe. If it is stuck, twist the end near the intake pipe carefully before pulling it off.


Disconnect the Intake Pipe
  Disconnecting the Intake Pipe
  • Loosen the two hose clamps at the ends of the intake pipe. The Turbo models have two hoses to disconnect at the end toward the front of the car.
  • Disconnect both ends of the intake pipe and lift it out of the engine bay. The fittings are pretty tight, so you may have to wiggle it a bit to get it loose
Note: Non-turbo shown above, Turbo shown below.


Remove Intake Pipe
  Removing the Intake Pipe
  Now that the pipe is disconnected, remove it from the engine bay.


Disconnect Brake Booster Hose
  Disconnecting the Brake Booster
  Remove the brake booster vacuum hose by pinching the clamp to loosen it and then slide the hose off the nipple on the plenum.


Disconnect Fuel Pressure Vacuum Hose [All] And BPV Hose [Turbo only]
  Disconnecting the FPR Vacuum Line
  Remove the vacuum hose that goes to the fuel pressure regulator by sliding the hose off of the protrusion on the intake plenum. As with other hoses, if it is stuck, grasp the hose near the end and carefully twist it about the protrusion so as to break it free. It will then slide off. Note that the Turbo models will have another vacuum line that goes to the turbocharger bypass valve (BPV). That's the larger, disconnected red hose in the upper middle of the 2nd picture.


Remove the Throttle Body Stay Bolt
  Removing the Throttle Body Stay
  One 12mm (18 N*m) bolt secures the rear of the throttle body to the engine. Remove the bolt. Pretty, shiny throttle body courtesy Mopar Combustion Chamber Cleaner (Chrysler P/N 04318001).


Remove the Throttle Body
  Removing the Throttle Body
  Four 12mm bolts (13 N*m) attach the throttle body to the intake plenum. Remove the bolts, and the throttle body will now be free from the plenum and its mounting bolt. Gently pull the throttle body away from the plenum, being careful not to lose the gasket (next step). Note that the throttle body will still be attached to some coolant lines and some vacuum lines, so do not attempt to remove the throttle body from the engine bay.


Remove the Throttle Body Gasket
  Removing the Throttle Body Gasket
  The throttle body gasket is in between the throttle body and the intake plenum. Remove it, making note of the direction in which it is installed. Do not reinstall the used gasket - replace it with a new one!


Remove the Intake Plenum Stay Bolts
  Removing the Intake Plenum Stay
  There are three 12mm (18 N*m) bolts that secure the rear of the intake plenum to the engine. Remove the bolts, noting that one bolt also secures a grounding cable to the chassis.
Remove EGR Connections [If Applicable]
  All Turbo cars, all OBD-II cars (1996 and later), and California-spec Non-Turbo cars from 1991-1995 are equipped with an exhaust gas recirculation (EGR) system. You'll need to disconnect the valve and the inlet pipe on the rear of the plenum to remove the plenum from the car. There are two 12mm bolts on the EGR inlet pipe (foreground in 1st picture, right side in 2nd picture) and two more 12mm bolts on the EGR valve (farther back in 1st picture, left in 2nd picture). Note that the second picture shows the plenum completely removed simply because it made showing where the parts are much easier. Getting a camera in the space above the rear turbo is difficult.



Remove the VIC Motor Wiring Harnessess [Non-Turbo Only]
  Removing the VIC Motor Connections
  There are two wiring harnesses attached to the Variable Induction Control(VIC) Motor. There is a silver wire clip (looks like a paper clip) that surrounds the harness connector. Carefully remove this with a small screwdriver. Then the harness connector will just slide off.


Remove the Remaining Intake Plenum Bolts
  Removing the Plenum-Manifold Connections
  There are five more 12mm bolts (18 N*m) and two 12mm nuts (18 N*m) that attach the intake plenum to the intake manifold. Remove the bolts and the nuts, being careful not to let the lock washers or the nuts fall down into the murky depths of the engine bay, lest you never see them again.


Lift the Intake Plenum Out of the Engine Bay
  Removing the Plenum
  At this point, the intake plenum is not connected to the engine, so you can simply lift it out. Do this carefully, and lift straight up until you clear the posts on the manifold. The picture shows the plenum partially lifted out, but not removed. You can also see the metal plenum-manifold gasket on top of the intake manifold.


Remove the Intake Plenum Gasket
  Removing the Plenum Gasket
  The intake plenum gasket lies between the manifold and the plenum and can be removed once the plenum is removed. This gasket must be replaced whenever the intake plenum is removed, as should all such gaskets. You now have access to all 6 spark plugs and wires. A few points of interest and the cylinder numbers have been labeled for reference.


Random Pictures of Manifold and Plenum [Turbo]

  These are pictures of a TT engine in good health with about 60,000miles on the clock. Water injection was installed about a week before these pictures were taken, and you can already see that the intake runners are getting cleaned out from the water.



Remove the Coil-side Connections of the Ignition Wires
  Removing the Coil Side Ignition Wires
  Gently pull straight up. Repeat for remaining 5 cylinders. Note that the numbers are actually printed on the engine approximately where the green numbers are located. From the front of the car, the connections are: 6, 3, 5, 2, 4, 1


Remove the Plug-side Connections of the Ignition Wires
  Removing the Plug Side Ignition Wires
  Again, gently pull straight up; repeat for remaining 5 cylinders.


Remove Spark Plugs
  Removing the Spark Plugs
  With your spark plug socket on a 6" extension attached to your socket wrench, gently remove the spark plugs from the spark plug wells. As you remove the spark plugs, place them somewhere where you can later remember which plug came from which cylinder as this can help diagnose problems. When replacing the spark plugs, tighten them to 25 N*m with your torque wrench so you don't strip the threads!


Inspect Spark Plugs

  These plugs had about 10,000 miles on them and came out of a healthy turbo engine.


Reverse the Instructions to Reinstall Everything
  Nuts and Bolts You Removed
  In case you forget where all the nuts and bolts you removed are supposed to go, here's a picture of all the parts you should have lying around if you're working on a Non-Turbo car without EGR. I've included the torque specifications in the above descriptions for each of the bolts you will be tightening. While it is not absolutely necessary to use a torque wrench, it is highly recommended, especially on the connections involving metal gaskets. If you have a car with EGR connections, don't forget the (4) extra 12mm bolts you'll have, and if you have a turbo car, don't forget the two extra 12mm bolts for the rear turbo compressor outlet pipe. [Clockwise from top left]
  • Intake Plenum Stay Bolts (With Washers)
  • Accelerator Cable Bracket Bolts (With Washers)
  • Wiring Rail Bolts (With Washers)
  • Wiring Harness Bolts (No Washers)
  • Throttle Body Bolts and TB Stay Bolt (With Washers)
  • Intake Plenum Nuts and Lock Washers (With Washers)
  • Intake Plenum Bolts (With Washers)
  • Intake Plenum (not pictured)

Wanna check your cylinder compression while you've got the plugs out?

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Last Modified Fri Jun 04 2004 18:08:12 PDT