My 911 temperature gauge doesn't have any markings on it. How do I know
what temperature it's operating at?
If your temp gauge is like mine, it has a wide white band near the
bottom ("warm-up band"top of this band is 140F or 60C), then a white tick
mark (200F or 90C), a second white tick mark (250F or 120C), and a wide red band (bottom
of this band is 300F or 150C).
What the heck is this thing called the RPM transducer?
The rpm transducer is used to
activate the shut-off solenoid on the MFI pump. It prevents the pump from continuing to
pump fuel into the engine when coasting at high speed, which will result in backfiring and
The rpm transducer puts
out 12v above about 1600 rpm, and 0v below it. Its connected to the MFI shut-off
solenoid through a microswitch thats activated by the accelerator linkagethe
one on the left side of the engine, attached to the input stacks. With your foot off the
accelerator, the switch is closed, and if the engine speed is above 1600 rpm, i.e.,
youre coasting at speed, then 12v is applied to the relay and it shuts off the pump.
If youre below 1600 rpm, even though the switch is closed, i.e., youre idling,
the solenoid is not activated because the sensor is putting out 0v, and fuel is pumped to
The transistor leads corrode and break over time. Virtually any
generic NPN, like a 2N2222, will work.
The 911 uses a "dry-sump"
system, as opposed to the "wet-sump" system used by most passenger cars. In a
dry-sump system, the oil at the bottom of the crankcase is picked up by a pump which sends
it to an oil tank. After being de-aerated (completely) and cooled (somewhat) in the tank,
another pump sends oil from the tank to the engine. After flowing through the engine, it
ends up in the bottom of the crankcase again, and the cycle repeats.
When you measure the oil
level on the dipstick, youre measuring the level IN THE TANK. Thats why you
must measure the oil level while the engines idling; if the engine isnt
running, some oil will be in the crankcase, and your dipstick will erroneously read low.
How do I set the mixture properly on my 911 CIS motor?
procedure is to use a high-impedance (digital) dwell meter to measure the duty cycle of
the CIS frequency valve. You can do this from the test connection inside the electrical
panel at the left rear drivers side of the engine compartment. Its the little
black plug with a cap, near the CD box. Inside are three connector pins. Connect the
positive lead of the dwell meter to the green/white wire pin, and the ground to the brown
wire pin. When the engine is at normal operating temperature, the reading on the dwell
meter should dither around 45 degrees (using the 4-cylinder scale), typically ranging from
40 to 50 degrees. This translates to 50 percent duty cycle, meaning that the frequency
valve is on half the time, and that your basic mixture setting is good. (If you are lucky
enough to have a meter that measure duty cycle, obviously you are looking for about 50
If you see a higher dwell
reading, say 70 percent, it means that the system is trying to control a basic mixture
setting that is too lean. Conversely, if you see a low reading, say 30 percent, it means
that the basic setting is too rich.
The mixture is adjusted using a special
3mm Allen wrench, through the hole between the fuel distributor and the rubber air duct.
Turning this screw to the right makes the mixture richer, left makes it leaner. Never blip
the throttle while the wrench is in the hole, or you may bend the air sensor plate. Also,
you want to finish the adjustment by turning to the right.
All of the above assumes that you are
working on a 80-83SC, with the Lambda oxygen sensor. Correct basic mixture setting helps
smooth transition from cold start to warm running, and overall efficient operation.
Which oil cooler is the best upgrade for the older tuba style types on the early
best cooler for an SC is the 87 Carrera cooler, with the thermostat and fan. I tried
the Terbatrol and the 28-tube brass cooler, without much improvement. If you get the
Carrera cooler, I recommend that you have it ultrasonically cleaned before installation.
The 87 Carrera fender brace allows you to relocate the horns for proper clearance,
so get it too.
Also, you may wish to install a
manual switch for the fan. A rear window wiper switch in the stock position works well. If
you need more info, including a wiring diagram, send an SASE to 30822 Alta Mira Drive,
Redlands, CA 92373.
I've got this annoying clutch chatter on my 911SC? What is causing
This is for models with
auxilliary clutch spring (C-Shaped spring on bottom of transmission)
In trying to fix
slight, occasional clutch chatter in my SC, I chased down Technical Bulletin 8403,
Subject: Clutch Chatter. The entire text (no pictures) is:
complaint of clutch chatter, first check that the clutch cable guide tube is not
contacting the accelerator linkage. If contact is being made, adjust the guide tube to
ensure adequate clearance will be maintained."
I replaced the
clutch cablethe new one is plastic coated cable running in a plastic sheath, versus
the old bare wire cable in plastic sheath. The clutch action is noticably lighter and
smoother. The chatter is gone. I think the old guide tube was rubbing against the
transmission, maybe binding on the filler plug.
mounts also can cause chatter. They are easy to check, just support the motor with a floor
jack and remove one of the rear mounts for inspection.
If this type of
cable system has inadequate bow in the bowing tube, it can cause clutch chatter. To
increase bow, adjust the cable at the pedal end (under carpet at front of tunnel, under
dash) so that the threaded end of the cable just protrudes inside the yoke of the clevis.
This provides maximum cable length, and therefore maximum bow in the bowing tube.
Additionally, ensure that the clutch auxilliary spring is clean, lubricated, and free of
caked-on cosmoline, as this can also contribute to chatter.