Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
MFI simplification thread (1st draft)

The Bosch “timed indirect injection” or mechanical fuel injection (MFI) system used on early 911s up until the factory changed to a mechanical continuous injection system (CIS) half way through the 1973 model year is one of the most complex yet rewarding fuel delivery systems ever used on a production car. Below is an attempt to describe the various components of the MFI system in an easily understood manner. The goal is to make the operation of the system more understandable and thus assist with repair diagnosis. Please view this as an open solicitation to those with knowledge of the MFI system to suggest additions, deletions or modifications to any of these descriptions. I’d also like to add my thanks to all those who contributed to the original post which fleshed out some of these definitions. Here goes ...
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)
Old 02-05-2008, 01:56 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
MFI Overview

MFI Overview: The Bosch Mechanical Fuel Injection system is designed to inject exact quantities of fuel in relation to inducted air to achieve better combustion of the air fuel mixture. The system is comprised of two main parts, the Injection Pump and the Control and Compensating Unit. The main elements of the Injection Pump are the pump camshaft, roller tappets, injection plungers and plunger control rack. All of these elements are lubricated by the engine lubrication system through a connecting line and filter and an oil return line to the crankcase. The Control and Compensating unit’s major elements are the contoured cam and roller sensor, centrifugal governor, shut-off solenoid, enrichment solenoid, thermostat and barometric cell.

Operation: An electric fuel pump designed to deliver fuel at a rate of approximately 29 gallons per hour delivers fuel from the tank to the fuel filter. The fuel filter contains an overflow valve which regulates the fuel flow at approximately 12psi to the injection pump. The fuel pump is specifically designed to provide excess fuel capacity so that the injection pump stays a cool as possible. The excess capacity is routed back to the fuel tank via a return fuel line. The ignition pump is powered by a “spur belt” running off the left engine camshaft. The pump contains six injection plungers which are actuated by the injection pump camshaft. The plungers force fuel through six pressure lines of equal length into the injection nozzles in the cylinder heads at a pressure of approximately 210-265 psi. This system is known as “timed indirect injection” because injection is timed so that fuel is injected into the inlet valves just as they begin to open.

When the car is started and the accelerator pedal pressed, air is drawn into the engine through an air cleaner then down two triple-duct velocity stacks bolted on the throttle bodies. The air/fuel mixture ratio is maintained at 14.8:1 (1 pound of fuel to 14.8 pounds of air) by a complex “compensating unit” featuring a contoured cam mounted on the control unit camshaft and moved axially and laterally by a centrifugal governor and by the accelerator linkage. A roller sensor riding on the cam relays the required fuel volume to the rack via a “control lever.” A barometric cell is included to compensate for outside air pressure, a thermostat reacts to varying engine operating temperatures and an enrichment solenoid (on pre-1971 pumps) or a “thermoswitch” (on post 1970 pumps) provides correct fuel enrichment. Finally, a shut-off solenoid cuts off fuel supply when the car is decelerating in gear. All of these devices work together to move the plunger control rack back and forth to compensate for external variations and assure that appropriate levels of fuel are provided.

Here is a picture of Porsche six cylinder engine with the Bosch MFI system.

© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-26-2009 at 03:03 PM.. Reason: Changed "14.8 psi" in paragragh 3 to "14.8:1 (1 pound of fuel to 14.8 pounds of air)". Thanks to Bill in post 27
Old 02-05-2008, 01:57 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Barometric Cell

BAROMETRIC CELL – compensates for changes in air pressure by varying the amount of fuel injected based on the atmospheric pressure. The barometer used on all timed indirect injection (MFI) Porsches is of the aneroid type and is made up of thin elastic metal disks contained in a chamber which sits on the top of the injection pump. The chamber is partially evacuated of gas and prevented from collapsing by a strong spring. The design of the chamber means that the barometer is not serviceable by a home mechanic. When the elastic metal disks are subjected to small changes in atmospheric pressure they are designed to shrink or expand. This expansion and contraction drives a mechanical lever inside the injection pump which alters the position of the control rack and allows the quantity of injected fuel to be increased when the car is operated at high air pressure (for example, sea-level driving) and decreased when operated at low air pressure (for example, mountain driving). The barometric cell is identified in the diagram of the post-1970 injection pump below.


© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)
Old 02-05-2008, 01:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Cold Start Solenoid

COLD START SOLENOID – located on the top of the fuel filter, this device is an electromagnetic switch that mechanically opens a circuit allowing fuel to be injected when electric current is run through it. When the starter is engaged, an electric current goes through a thermal sensor located at the top center of the crankcase. This thermal sensor measures engine temperature. If the engine is cold, current is allowed to pass through to the Cold Start Solenoid which activates allowing an injection of raw fuel to be sent to the intake stacks. When power is removed from the starter, the cold start solenoid is shut off to avoid flooding the engine. The purpose of the cold start solenoid is to supply extra fuel only when the weather is cold and the engine is harder to start. The cold start solenoid is identified at #4 in the diagram below.


© Dr. Ing. h.c. F. Porsche A.G., Factory Workshop Manual, Volume III, chapter 2, page 0.1-1/4. Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-26-2009 at 02:37 PM.. Reason: Corrected the diagram to show proper flow into and out of the filter. The diagram is incorrect in volume I, page SF12 of the factory workshop manual. Thanks to Grady Clay for spotting this error!
Old 02-05-2008, 01:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Control Unit

CONTROL UNIT – is located inside the Injection Pump. The control unit consists of a contoured cam mounted on a fixed camshaft together with a centrifugal governor that controls the speed of the engine by regulating the amount of fuel admitted so as to maintain a near constant speed whatever the load or fuel requirements. When the accelerator is pressed the contoured cam is rotated and moved forward, back and axially on the camshaft by the centrifugal governor (a mechanical transfer device) so that fuel delivery can be altered based on engine load or speed. Riding on the contoured cam is a small roller sensor. This sensor maps the information received from the rotary motion of the engine, the accelerator position, the atmospheric pressure (from the barometric cell) and the engine temperature (from the thermostat) and transfers that fuel volume information to the control rack by moving the governor control lever. The purpose of the control unit is to supply the engine with different quantities of fuel under varying engine speeds and loads. The control unit and its various parts are identified in the diagram below.


© Glenn’s Diesel and Gasoline Fuel Injection Manual. Posted here for educational purposes only.

Here is a picture of the three-dimensional space cam which is the heart of the control unit.

© Bruce Anderson's 911 Performance Handbook. Posted here for educational purposes only.



Paul, screen name pjh69911, proposed this clarification:

Quote:
The heart of the control unit is the 'contoured cam'. It is a 3-dimensional cam whose radial dimension varies both with rotation and with axial displacement. The 'governor control lever' (connected to the throttle) only acts to rotate the contoured cam. The 'centrifugal governor''s weights fly outwards with increasing speed, causing the contoured cam to move axially. The 'sensor on the contoured cam' moves radially in response to the rotational and axial contour variations, and thereby provides a specific output of radial displacement for any combination of throttle position and engine speed. This radial displacement of the sensor is fed to the flat metal plate with rectangular slots via the upper pin in the rectangular slot. The lower pin in the lower slot acts on the fuel rack. The ratio of the input upper pin to the output lower pin is influenced by the thermostat and barometric cell, that move the pivot center of the flat slotted metal plate, further or closer to the rack lower pin. Refer to earlier control compensating unit illustration.
If this makes more sense to the board I'll be happy to change the definition I suggested or merge the two. I just couldn't make a merger work but I'm open to suggestions!
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-06-2008 at 07:14 AM.. Reason: Add picture of "Space Cam"
Old 02-05-2008, 01:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Enrichment Solenoid

ENRICHMENT SOLENOID – is located beside the Thermostat on pre-1971 Injection Pumps. When the ignition is activated, a time-limit relay closes the solenoid circuit for two seconds moving it beyond the full power position and pushing the plunger on the control rack to allow maximum fuel rate delivery for starting. When engine temperature is below 50° Fahrenheit, a thermo-limit switch keeps the circuit closed for an appropriate period of time to allow additional fuel for starting. The purpose of the Enrichment Solenoid is to enrich the combustion mixture in cold or hot starting conditions. The Enrichment Solenoid was removed from the Injection Pump beginning in Model year 1971. On 2.2 and 2.4 liter engines, a thermoswitch in the breather cover operates the cold start valve. The pre-1971 Enrichment Solenoid is pictured below and at # 28 in the diagram of the early Injection Pump.



© Haynes Porsche 911 Automotive Repair manual. Posted here for educational purposes only.


© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.

Here is a picture of the thermo-time switch which keeps the enrichment solenoid closed longer than the 2 second time limit relay to assist with starting very cold engines. The picture is from this thread: cold start enrich '71E



The function of the thermo-time limit switch is shown in this diagram from the same thread (originally from the CMA manual).

© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-05-2008 at 03:07 PM.. Reason: Add picture of thermo-time limit switch
Old 02-05-2008, 02:00 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Mechanical Fuel Injectors

FUEL INJECTORS - The six fuel injectors used in the Bosch MFI system are mechanical in operation. They are threaded into the cylinder heads behind each intake valve. The injectors operate by opening up when fuel is forced through the hard fuel line connected to the injector and through a filtering screen at approximately 210-265 psi. The fuel comes in from the bottom of the injector and is forced upward against a spring, where it forms a cone and is finely atomized and sprayed out of the injector into the intake port (a picture of proper fuel atomization is shown below). The injectors should be tested regularly to assure that they hold pressure and have a perfect spray pattern with a nozzle tester similar to the one shown below.

Below is a picture of a Bosch mechanical fuel injector for the MFI system:


Here is a picture of the appropriate nozzle spray pattern for the Bosch fuel injectors:


Here is the mechanical nozzle tester used to check for leaks and spray pattern.

© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-06-2008 at 03:58 PM.. Reason: Fix Typo
Old 02-05-2008, 02:00 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Fuel Pump

FUEL PUMP – is an electric roller-cell type with a delivery capacity of up to 33 gallons per hour. The pump is mounted on a bracket under the fuel tank. The fuel is delivered from the tank to the fuel filter. The fuel filter contains an overflow valve which regulates the fuel flow at approximately 12psi to the injection pump. The fuel pump is specifically designed to provide excess fuel capacity so that the excess fuel can be used to cool the injection pump. After flowing through the injection pump, the excess capacity is routed back to the fuel tank via a return fuel line. If fuel pressure increases above 14psi, an independent bypass valve installed in the fuel pump routes excess fuel to the fuel tank.

The Exact Fuel Pump Specifications are:
Regulated pressure = 14.2 PSI, 0.8±0.2 Bar
Flow rate = 125 liters/hour
Porsche P/N = 901.608.105.00
Bosch P/N = 058097 0001
Current draw = 3.5A @ 12V
RPM = 2800

The fuel pump is # 2 in the Fuel Injection System Diagram and its location is shown in the diagram below.


© Chilton's Porsche 2 Repair and Tune-Up Guide (1973). Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-06-2008 at 02:20 PM.. Reason: Fix typo
Old 02-05-2008, 02:01 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Injection Pump

INJECTION PUMP: The MFI Injection Pump consists of two major parts: (1) the pump assembly which contains the camshaft (#19 below), the six plunger units (#s11-14 below) and the toothed control rack (aligned horizontally behind #27 below); and (2) the control and compensating unit (described above). Each of the six plunger units consists of a plunger and a cylinder. Each plunger has teeth which mesh with the control rack on top and a roller tappet (#20 below) which rides up and down on one of the camshaft lobes on the bottom. As the camshaft rotates, the movement of the lobes forces the tappet into the plunger. At the same time, the various components of the compensating unit (thermostat, barometer, enrichment solenoid, etc) are sending instructions via connecting levers to the toothed control rack causing it to slide back and forth in the teeth of the plunger. This movement of the control rack causes the plunger to rotate exposing a slanted "metering land" in each plunger. This metering land is designed to close or open the inlet port to the fuel injector (see diagram below). The amount that this inlet port is open determines the quantity of fuel to be delivered with each stroke. As a result of these complex movements, the fuel contained in the plunger chamber is forced out in appropriate quantities through the hard fuel pressure lines then through the injectors and into the intake port.


pre-1971 MFI Injection Pump

© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.


Pump Plunger and Cylinder showing fuel delivery.

© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-07-2008 at 01:36 AM.. Reason: Fix Typo
Old 02-05-2008, 02:01 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Thermostat

THERMOSTAT - The thermostat is located on the front of the injection pump and is one of the compensation units on the pump along with the barometric cell and the enrichment solenoid. Its purpose is to compensate for various engine operating temperatures. The unit consists of several pairs of thermal expansion discs which shrink or expand based on engine operating temperature. The thermostat receives its heat signals from a double walled hose connected to the driver's side heat exchanger. When the engine is cold, the control rack is set to fully enrich the fuel mixture for easier starting. As the engine warms up, hot air is feed through the hose to the thermostat. This causes the discs to expand moving a lever in the injection pump which alters the control rack to lean out the mixture. Thermostat has no effect on the control rack after a temperature of approximately 113°. The thermostat is number 1 in the diagram of the Ignition pump above. Here is a detailed schematic of the thermostat and the expansion disks:

Schematic drawing of MFI Thermostat.

Copied from the MFI thermostat spacers thread. Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-07-2008 at 01:40 AM.. Reason: Label diagram
Old 02-05-2008, 02:02 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Shut-Off Solenoid, Micro-Switch and RPM Transducer

SHUT-OFF SOLENOID, MICRO-SWITCH AND RPM TRANSDUCER CIRCUIT: The shut-off solenoid is part of the control and compensation unit (on the lower right in the diagram below). Its function is to move the control rack to the fuel off position when the vehicle is decelerating in gear. The shut-off solenoid is controlled by a micro-switch in the accelerator linkage and an RPM Transducer on the relay panel which receives its RPM signal from the distributor. The RPM transducer senses engine speed. It is supposed to activate the shut-off solenoid cutting off the fuel supply when the throttle is closed (for example when the car is decelerating) and engine speed is above 1,500 RPM. If everything is working correctly, the solenoid is supposed to release when the RPM transducer senses engine speed dropping below 1,300 RPM regardless of throttle position. This allows the fuel supply to resume and the car to idle correctly. If engine speed is again increased, the solenoid circuit is interrupted by the micro-switch allowing the RPM transducer to again become activated at 1,500 RPM.


© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.

The RPM Transducer is #5 in the diagram below and wired through #30b on the terminal.

© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.

Here's a schematic of the RPM transducer thanks to Warren Hall - "Early S. Man" (may he rest in peace) and Mike Gillies of Brisbane, Australia.


Finally, below is a simplified wiring diagram and description for the micro-switch and RPM transducer (#5 in the schematic). * Provided by Pelican member Jim727.

Pin 1: Output to shutoff solenoid;
Pin 2: Power from engine fusebox;
Pin 3: Ground and pin 31 of time limit switch;
Pin 4: CD Ignition and distributor.

The RPM Transducer (also known as the "Speed Switch") receives a signal proportional to the engine RPM from the distributor (contact 1 on component 1 in the diagram); this signal is also used to trigger the CD Ignition pulses (contact "C" on component 3 in the diagram). Circuitry in the RPM Transducer bridges contact 1 to contact 2 (on component 5 in the diagram) when engine RPM is above 1500 and opens the connection when engine RPM is at or below 1300 and falling. The final link in the chain is the microswitch which allows the output of the RPM Transducer to energize the shutoff solenoid when the throttle is closed and the above conditions are met.


© Intereurope Workshop Manual, Porsche 912, 911T, 911E, 911S, page 62 (October 1972). Posted here for educational purposes only.
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)

Last edited by David E. Clark; 02-06-2008 at 03:55 PM.. Reason: Correct wiring description for RPM Transducer
Old 02-06-2008, 05:05 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered User
 
Join Date: Dec 1969
Posts: 923
Very nice. Thanks for all the work to put this info together.
Old 02-06-2008, 07:06 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
 
Tree-Hugging Member
 
Jim727's Avatar
 
Join Date: Oct 2006
Location: Northern California
Posts: 1,676
David -

It still says "...RPM Transducer on the relay panel which receives its RPM signal from the ignition coil". Your diagram indicates othewise.

Jim
__________________
~~~~~
Politicians should be compelled to wear uniforms like NASCAR drivers, so we could identify their owners.
~~~~~
Old 02-06-2008, 12:57 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Registered User
 
Join Date: Dec 2004
Location: Montgomery, AL
Posts: 689
In the "Fuel System" figure, the fuel pump in the diagram is #2, not #1
__________________
Steve B.

1972 911t
1999 328is
Old 02-06-2008, 01:21 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Quote:
Originally Posted by Jim727 View Post
David -

It still says "...RPM Transducer on the relay panel which receives its RPM signal from the ignition coil". Your diagram indicates othewise.

Jim
Jim,

Can you please explain what you are talking about in more detail? As I understand the system, the RPM Transducer gets it's RPM signal from the ground connection on the coil. I agree that it was confusing to say that they are "connected" but unless I've been misinformed (or read my reference materials wrong) the RPM signal is from the coil. This is what I'm trying to say anyway! Can you think of a better (or less confusing) way to say this?

I found this description of the RPM Transducer on the Question and Answer page but it doesn't help with this issue:

Quote:
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
btindel@gte.net
Quote:
Originally Posted by sballard View Post
In the "Fuel System" figure, the fuel pump in the diagram is #2, not #1
Thanks Steve. Even I should be able to tell the difference between the fuel pump and the fuel tank!
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)
Old 02-06-2008, 02:43 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Tree-Hugging Member
 
Jim727's Avatar
 
Join Date: Oct 2006
Location: Northern California
Posts: 1,676
Pin 1: Output to shutoff solenoid;
Pin 2: Power from engine fusebox;
Pin 3: Ground and pin 31 of time limit switch;
Pin 4: CD Ignition and distributor.

The RPM Transducer (also known as the "Speed Switch" receives a signal proportional to the engine RPM from the distributor (contact 1 on component 1 in the diagram); this signal is also used to trigger the CD Ignition pulses (contact "C" on component 3 in the diagram). Circuitry in the RPM Transducer bridges contact 1 to contact 2 (on component 5 in the diagram) when engine RPM is above 1500 and opens the connection when engine RPM is at or below 1300 and falling. The final link in the chain is the microswitch which allows the output of the RPM Transducer to energize the shutoff solenoid when the throttle is closed and the above conditions are met.
__________________
~~~~~
Politicians should be compelled to wear uniforms like NASCAR drivers, so we could identify their owners.
~~~~~
Old 02-06-2008, 03:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296
Great explanation! Thanks. I made the changes. Is it clearer now?
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)
Old 02-06-2008, 03:51 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #17 (permalink)
Tree-Hugging Member
 
Jim727's Avatar
 
Join Date: Oct 2006
Location: Northern California
Posts: 1,676
Works for me. Good stuff.

Jim
__________________
~~~~~
Politicians should be compelled to wear uniforms like NASCAR drivers, so we could identify their owners.
~~~~~
Old 02-06-2008, 04:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #18 (permalink)
Autodidactic user
 
David E. Clark's Avatar
 
Join Date: May 2003
Location: Summerfield, NC
Posts: 1,296


Now that I've got your attention. Any more corrections, additions or deletions?
__________________
Please help the MFI community keep the Ultimate MFI resources thread and the Mechanical fuel injection resource index up to date. Send me a PM and I'll add your materials and suggestions.

1973 911E Targa (MFI)
Old 02-09-2008, 02:36 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #19 (permalink)
Max Sluiter
 
Flieger's Avatar
 
Join Date: Mar 2006
Location: So Cal
Posts: 19,573
Garage
What is the function of the injectors which go into the intake stacks?

From another thread, I believe that they are responsible for enrichment for cold start, etc.

My stacks are plastic. The injector is on the inside on each runner. Each is connected to a braided fabric line which eventually connect together and then lead to the top of the fuel filter. Is it clear what I mean?

I want to know how these work and whether mine need to be modified, as I have no heater, therefore thermostat/cold enrichment circuit. I have a screw type adjustment. Also, I have no plenum on the motor presently.

Thanks for any information!
__________________
911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 02-10-2008, 03:10 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #20 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 

Tags
mfi


All times are GMT -8. The time now is 05:24 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.