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Home > Tech Info Center > The 911 Series > 911 Q&A > Page #2

Pelican Parts: 911 Questions & Answers
asked by our readers
Page #2

     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).

Bob Tindel

    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 other unpleasantness.

     The rpm transducer puts out 12v above about 1600 rpm, and 0v below it. It’s connected to the MFI shut-off solenoid through a microswitch that’s activated by the accelerator linkage—the 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., you’re coasting at speed, then 12v is applied to the relay and it shuts off the pump. If you’re below 1600 rpm, even though the switch is closed, i.e., you’re idling, the solenoid is not activated because the sensor is putting out 0v, and fuel is pumped to the engine.

The transistor leads corrode and break over time. Virtually any generic NPN, like a 2N2222, will work.

Bob Spindel

     What is the correct torque value for the oil drain plug on the bottom of the engine?

    The correct torque setting for the oil tanks drain plug and also the oil screen cover is 42 Nm or 31 ft-lb.

terry steer

     What exactly is a dry oil sump system?

     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, you’re measuring the level IN THE TANK. That’s why you must measure the oil level while the engine’s idling; if the engine isn’t 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?

     The 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 driver’s side of the engine compartment. It’s 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 percent.)

     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.

Bob Tindel

     Which oil cooler is the best upgrade for the older tuba style types on the early cars?

     IMHO, the 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.

Bob Tindel

     I've got this annoying clutch chatter on my 911SC?   What is causing this?

     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:

     "For a 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 cable—the 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.

     Defective motor 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.

Bob Tindel


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