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Dick Hussey's Tech Corner

1993 Allanté Plenum Replacement


If you haven't done so already, a good preventative measure is replacing the fuel pressure regulator of the 1993 Allanté. If you are purchasing a 1993 Allanté, ask if this has been replaced. The smell of gas may be the only warning you get if your fuel pressure regulator fails.



Do you hear what sounds like a backfire under the hood? That may be a cracked lower plenum that needs to be replaced along with your fuel pressure regulator, especially if you have an early model 1993.



The fuel pressure regulator for the Northstar engine is mounted inside the plenum under the intake cover. Early 1993 Northstar Allanté engines were produced with rigidly mounted intake plenum covers with the nut resembling an acorn securing the cover to the top of the lower intake plenum.

When a fuel pressure regulator fails, it leaks gasoline into the plenum and a plenum explosion might occur causing something to give. With the rigidly mounted cover, the weakest link appears to be the aluminum intake plenum. A cracked intake plenum wilt produce an uncontrollable high idle speed, usually in excess of 2000 RPM. Once cracked, the lower plenum must be replaced. By the end of 1993 Allanté production, the design of the plenum cover had changed slightly, along with the mounting hardware to secure this cover to the top of the lower intake plenum. The round nuts with Torx sockets are on the newer models. ﷯ The first few steps are the same if replacing your fuel pressure regulator or replacing your intake plenum. Relieve fuel pressure inside the fuel rail only when the car is cold! Best method would be to use a fuel pressure gauge and a relief line. The less desirable way uses a small screwdriver and a rag near the Schrader valve fitting. Once the fuel pressure has been relieved, make sure you do not turn the ignition on again until the job is complete. Disconnect the front four spark plug wires and the wiring conduit, and lay it off to the side. ﷯ Remove the air inlet duct. Allanté Source


Remove the twelve intake plenum cover retainers. Lift off the cover.



The early style employs 8mm acorn nut style heads. The upgraded style wilt urilize a T30 mm Torx socket to unscrew the large diameter heads. Make sure you keep track of the large rubber grommets under the later style bolt heads. These rubber grommets are used to absorb the force of the explosion if one should occur. The cover lifts about ¼ of an inch to vent the force created. This venting saves the

plenum from damage.


Once the cover has been removed, if all you are doing is replacing the fuel pressure regulator, locate the regulator. It is under the fuel rail wiring harness cover, near the throttle body. You will see a small vertical port coming out of the top. Pick up the

harness cover to access the fuel pressure regulator, then pull the regulator out of the harness cover and free of the plastic fuel rail pipe.


New Delco fuel pressure regulators come with the lower seal and retainer separately in a small bag. It is imperative that these pans be installed in the bottom of the fuel pressure regulator prior to installing the regulator in the car.


If the plenum is being replaced, take off the throttle body by removing the four T-40 Torx head screws that hold the throttle body to the plenum.

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It is easier to disconnect the throttle body from the plenum and leave everything else attached to the throttle body.



Next locate and disconnect the wiring harness connectors that come out of the bottom driver side front corner of the plenum.



There are blue locking clips that must be removed prior to separating the connectors. Next remove the four bolts that secure the plenum to the engine.

Article Reprints from the Allanté Insider





﷯ Once the plenum is loose, there is one vacuum line pointing to the rear over near the throttle body mount that must be disconnected. ﷯ Disconnect smaller vacuum lines in the area of the EGR valve. ﷯ The last remaining challenge is disconnecting the two flexible fuel lines that are located to the rear of the plenum and under the power brake booster. It is highly recommended that you obtain the correct tool to disconnect these lines. ﷯ Allanté Source Page 3

The fuel line retainers are a four leg internal spring clip, and all four legs must be depressed to clear a small flange on the end of each metal tube. You can use a small pick and small screwdriver, but this

takes significant patience and perhaps a little bit of luck in a confined area. If the ends are destroyed during removal, they will have to be replaced all the way back to the fuel tank. With the tool properly

inserted, they release easily. Place rags over the exposed intake ports so nothing falls inside while exposed.



Notice the starter motor tucked in the valley between the rags.


To this point, these instructions can also be used for Northstar starter replacement.


Once the lines have been disconnected, the plenum can be lifted off.



Remove the injector harness and injectors and fuel rail from the old plenum. The replacement plenum will need to be fitted with the new fuel pressure regulator, the fuel rail, fuel injectors, and injector harness prior to being reinstalled on the engine.


Once these parts have been installed on the replacement plenum,



clean off the bottom surface of the plenum before



removing the rags and reinstalling the plenum back on the engine.



Reconnect the throttle body, fuel lines, vacuum lines, and harness connectors.

﷯ If you had an early style cover, try to replace it with a later style cover with the round grommets. ﷯ Finally, reinstall the spark plug wires, spark plug wire retainer, and air inlet duct. Allanté Source ﷯

Before starting the engine, it is a good idea to turn the ignition on then off a few times to pressurize the fuel system and check for any evidence of fuel leakage.



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