Porsche 928 S4 Service

John Pirtle, October 7, 2002
http://members.rennlist.org/pirtle

Intake manifold

Two excellent references are available for this job. David Chamberland's reference article is in the Journal on the 928 Owners Club site, and Fred Rourke's is in my email keepers. David Schmidt has posted some fabulous pictures of his '90 GT Flapectomy.

The official procedure is in the Porsche Workshop Manual on page 24-223 under the title "Removing and Installing Rotary Idle Actuator" (eleven steps for removal, and three for installation!). However, an absolutely invaluable diagram showing all vacuum connections and hoses is on page 24-216 (see below).

There are many reasons for this job -

replace the intake flap actuator (the vacuum diaphragm tears)
replace ten hoses (something like oily, dried, crumbly play-dough)
replace six gaskets (think baked, hard, and crusty)
replace the oil filler gasket (you may have an oil lake in the "Vee")
replace two knock sensors (the connectors melt)
replace three vacuum lines (cooked and leaky)
clean, blast, and powdercoat metal parts

New intake parts

This is also a good opportunity to replace the fuel pressure regulator and two dampers, and have the fuel injectors cleaned.

I did not remove the crossbrace as specified in the Workshop Manual. I also attempted to remove the manifold without removing the fuel rails, but the passenger side would not clear the crossbrace.

Torque values
from the Workshop Manual pages 10-07 and 24-224

	Nm	ftlb
intake manifold nuts	15	11
throttle-body housing bolts	20	14
knock sensors	20	15
fuel rail mounts	15	11
intake manifold temp sensor	40	30
NTC II temp sensor	12	9
coolant temp sender	25-30	18-22
All other nuts and bolts M 6	8	6
M 8	20	15
M 10	40	30

Intake manifold diagram
from the Workshop Manual, page 24-216
(click for larger image)

Hose part numbers are in blue.

1 - Fuel pump
2 - Fuel filter
3 - Fuel line
4 - Distributor-type fuel injection tubes
5 - Injectors

A - Throttle housing
B - Idle speed actuator
C - Intake jet pump
D - Pressure damper
E - Pressure regulator
F - Vacuum valve
G - Electric tank breather valve
H - Oil filler neck
I - Secondary-air valve
K - Vacuum-operated switch valve (tune-intake flap)
L - Vacuum unit (tune-intake flap)

a - from fuel tank
b - to fuel tank
c - from activated charcoal cannister
d - from vacuum reservoir
e - to automatic transmission

Before installing the fuel rails, I wrapped them in some 1/2" (inner diameter) pipe insulation (Home Depot, $1.49).

Tuning flap

If you have your intake powdercoated you will need to remove the tuning flap (popularly called the "flappy"). During the powdercoating process the heat will melt the plastic piece under the spring, and pretty much kill the spring too.

Pop the actuator's cup off the ball of the flap pivot, and remove the two hex bolts that attach the actuator to the intake manifold. Remove the side covers from the "air distributor". The flap is held in place with two screws. Remove them and carefully slide the flap plate out of the pivot - note that the edges are cut at an angle and may be sharp.

Next remove the E-clip and washer from the top of the pivot. Then from underneath pull the pivot out. Be sure to block off the holes to protect the upper and lower bearings (or remove and replace them too).

Powdercoating

A previous owner had painted the intake while it was still installed. In some areas the original paint was flaking away.

I took the manifold and the oil filler neck (mine is the alloy version) to be sandblasted.

The powdercoater finished the pieces in bright silver and then added a clearcoat. As a porous magnesium alloy it is important that the pieces are first baked to outgas the metal. Otherwise when the powdercoat and clearcoat are heated the trapped gasses will be released and the finish will blister.

A future project is to do my valve covers - red!

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