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NINES, The SAAB Club Newsletter
TECHINICAL
TALK
Technical articles written by subscribers may recommend procedures
Or parts not approved by Saab-Scania of America, Inc. The SAAB Club
and NINES cannot stand behind the correctness of information in these
articles, but offers them based solely on the experiences of the writers.
Early 99 fuel systems
There has been a lack of articles lately
pertaining to early 99s, i.e. pre-'74. The follow-
ing describe the fuel systems of those models.
They are reprinted from the January and April,
1976 issues.- TW
Throttle Position Switch
There seems to be an absence of
knowledge about the workings of the
Throttic Position Switch (TPS) in 99s with
Bosch Etectronic Fuel Injection (EF1), and
| hope the following will be informative, if
not helpful.
This pertaing to '70 -"74 99s, and while
two different units are used, one for 1.7 &
1.85 liter engines, and one for 2.0 liter
engines, they perform the same basic
functions.
The throttle position switch or throttle
valve switch as it is also called, serves both as
an acceleration pump (on a typical carb)
and as a deceleration valve, (such as that
used on the later V4's),
Because of the design of the small
printed circuit inside the switch, upon
depression of the accelerator, the control
box (computer) signals the injectors to
spray, in very rapid succession, small
amounts of fuel, which makes for a
momentary lag in response. Additionally,
the TPS on the 2.0L engine provides for full
throttle enrichment, in an effort to suppress
detonation.
On the Decel side of the switch, there
are points which are normally open during
cruise, but with trailing throttle the points
close and allow the injectors to cease
injecting (no signal from trigger points) and
the engine decelerates both smoothly and
without polluting the air during this, the
next most dirty mode of operation. (Idle is
worse), In the long run, it also improves
one's gas mileage, especially ifa great deal
of city driving is done,
Very often the TPS will be out of
adjustment in such away that even during
Decel the injectors are still operating. It
does not get out of adjustment by itself.
There are those owners and mechanics who
have insufficient data as to the care and
feeding of the switch, and since they cannot
adjust it properly, put it way out in left field
as (6 forget it. When I say that they can’t
adjust it properly, it’s actually a matter of
patience and a thorough road test to see
that it is correct. If it is not right, one will
either have the injectors “on” all the while,
or ¢ven more fun, will have it in such a
position that at city cruising speed, in 2nd or
3rd gear, if the throttle is opened and closed
lightly the vehicle will begin a sort of ground
resonance that will put you through the
windshield and give you whip-lash almost
simultancously. A truly enjoyable experi-
ence. A homespun methad for adjusting
the TPS will get it in the bali park, and the
following method may be utilized.
We will assume that the setting is
incorrect, and therefore the two Phillips
screws may be loosened first. Then remove
the capacitor lead from the ignition coil
(primary lead) to keep from cooking the
points. Turn the ignition switch to the K
position and turn the TPS back and forth,
and you will notice a clicking noise coming
from two of the injectors. For easier
orientation, I shall describe the procedure
first for the 1.7 and 1.85 liter engines.
The shaft that the throttle position
switch is keyed to runs along the longitudi-
nal axis of the vehicle, so that the plastic
cover on the switch faces forward. fn this
position, movement of the switch will be left
Or right, as seen from the drivers seat.
Basically, rotating the switch right causes the
injectors to operate constantly, while
rotating it to the left causes them to shut off
during deceleration. Further rotation to the
left will cause jerking at cruise (as described
above) and at the left stop, the engine will
“hunt” at idle, if it will idle at all.
The procedure for the 2.0L engines is
the same except for the orientation of the
TPS. In this case, the throttle shaft which
the switch is keyed to runs along the lateral
axis. The cover for the TPS will face the
right hand side of the car, or towards the
cam cover. If we transfer the movements
above to the 2.0L TPS, we will have
injectors in continuous operation if the
switch is rotated towards the rear of the
vehicle, Conversely, rotation towards the
front results in Operating characteristics the
same as those described for “rotation to the
left” as noted above.
Earlier I mentioned a clicking noise
upon rotation of the TPS. It will normally
occur about in the center of the travel. As 4
rule of thumb, one will be safe if the TPS is
Set just on the offside of the click. 1.71. &
1.851: left; 2.0L forward.
After you've done this, tighten lock
screws, run engine and listen closely for the
injector sound at idle. Bring RPM’s to 3000
and clase throttle. At this point the injector
click should disappear, and only resume
after the engine has reached no higher than
1600 RPM's. A lower engine speed is OK,
as long as there is not t00 great a tendency
to stall,
One more check can be made, and it
goes like this: If the above has been
successful, open the throttle (again by hand)
and bring the RPM’s up to about 2,000,
then ever so slightly close the throttle until
RPM's begin to drop off, then hold the
throttle position. If the engine hunts at this
setting, it is adjusted too far towards the off
position and must be moved a few degrees
in the opposite direction.
Again, with patience and understand-
ing, this procedure will take only a short
time, all in the interest of reduced emissions,
better fuel economy, and the knowledge
that you did the job right, yourself!
John S. Fog
January, "76
injectors
Let’s look at two other components of
the EFI in the ongoing effort to supply a
degree of technical enlightenment for those
who desire it.
The injectors are solenoid operated
valves which are made up basically of a valve
SSS SSS
14
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Fluctuating idle - 99 carb
Should your ’69 - "74 99 equipped with
a Zenith Stromberg 175 CD exhibit a
fluctuating idle (up and down) one can
generally assume it is because of a malfunc-
tioning deceleration valve. First, one should
try to adjust it by turning the adjusting screw
gut couter clockwise (CCW), which
displaces a plunger in to increase tension on
the spring to push the brass valve tighter on
its seat. Should that fail, disassemble and
clean the valve and try again. Ef that docan’t
do the job, replace the decel valve (it causes,
problems with regular and frequent
ERORONN Tt is also referred to as the
“owerflow valve”.
Another accessory on your Zenith
Stromberg is the Temperature Compensa-
tor. This rarely causes trouble, but after
high mileage may get carboned up, and it
can be cleaned. It is closed when cold, open
On the early 175’s ("69 -'72) the CO is
adjusted by raising or lowering the metering
needle. On models "73 - m4 the Main Jeti
threaded and can be raised or lowered as
needed. The knob is on the bottom of the
float bowl, and raising it (clockwise) leans
the mixture, while lowering it (counter
clockwise) richens the mixture. These ad-
justments are best made with the aid of an
exhaust gas analyzer, to insure a compro-
mise between fuel economy and engine
_ power, capecially at full throttle.
Should one have one’s carb apart, it is
to be noted that the correct float level is
obtained when. the mold line on the plastic
float is parallel with the casing. Incorrect
(high) float level may cause stalling around
corners. The carb vent hole should be on
‘the portion of the carb towards the driver.
Also, if the ZS 175 CD equipped
vehicle refuses to run past idle, or will run
only with the choke on, one may very well
suspect the diaphragm has split. ‘Therefore,
the piston, which must move up and down
to act as a variable venturi, will in this case
remain stationary, hence the reluctance to
Tun property.
John S. Fog
January, '76