Porsche 924 Factory Service Manual
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Table of Contents
1. Cover.
2. Index
3. Forward, Purpose, Summary, Disclaimer
4. Introduction to CIS (Continuous Injection System)
5. Getting Started …First place to start your troubleshooting
6. Troubleshooting Chart ….Second place to look
7. Wiring Diagrams …Block diagrams that are easy to read
8. Theory of Operation … Know the sequence of events during engine start-up and run
9. Testing of Components (parts) …Test the suspected part
10. List of Fuel Injection Parts
11. Definitions …Know what the part does
12. Technical Information …Tune-up, idle speed, etc.
13. General lnformation …Horsepower. Compression, Torque, etc.
14. Photos of CIS Fuel Injection …Know what the part looks like
15. Tool List and where to find them
FAQ (Frequently asked Questions)
2
CIS TROUBLESHOOTING HANDBOOK FOR THE 73-83 PORSCHE 911
Compiled and Written by Jim Pennington
FORWARD
Have you ever taken a close look at the troubleshooting manuals today?
The information you receive is incomplete. At best,you get only general information.
Have you ever gotten to a point that you are frustrated with the time spent researching
material to just get your Porsche 911 running?
I have the solution to your frustrations.
I have written the best troubleshooting handbook for the CIS FUEL INJECTION system
for the non Turbo Porsche 911.
I have been in the fuel injection repair business for over twenty years. Each time I went to
work on a 911, I had to refer to a component list then refer to another book for the
specifications. I have made it easier for you to work on your car by having just one book to
refer to for information. This troubleshooting manual has troubleshooting charts geared to
your car. You will find photos, wiring diagrams, component location, component photos and
simple procedures to test the fuel injection in your Porsche 911.
PURPOSE
The purpose of this handbook is to provide .information in one easy to follow book. This book
will answer your questions on CIS fuel injection. It will allow you to follow simple instructions,
without having to refer to a number of other manuals. You will find that each year of the CIS
system is covered. This handbook will not go into the complete theory of operation of the
system. There are many books written on the subject. This handbook will help you with a brief
description of each component, photo, specifications and the procedures to test the
component.
SUMMARY
The hand book covers the CIS fuel injection on the non turbo Porsche 911 from 1973 through
1983. Tech Tips, troubleshooting charts, and" how to test" sections are clearly written. The
handbook is a reference book that all mid year Porsche 911 owners will want for their library.
DISCLAIMER
By using this hand book, the user assumes all responsibility of safety, possibility of damage to
the vehicle, and his/her ability to perform the tasks required.
The user of this handbook will be working around high gasoline pressures, hot temperatures
and electrical current, all of which are dangerous to the health of the user.
By using this handbook the user will hold the writer harmless of any damage or injury that
may occur.
This book is put together with information available at the time of printing. This handbook
is not meant to be the definitive answer to all CIS fuel injection problems. The person using
this handbook is assumed to have the mechanical ability and have the knowledge of the
mechanical, electrical and safety aspects of working with fuel on an automobile.
This handbook is for informational purposes only and if the user has any doubts of their
abilities, consult a specialist.
3
Introduction to CIS (Continuous Injection System)
There were two types of CIS used on the Porsche 911 from 1973 through 1983.
They are the K-jetronic and K-jetronic with Lambda.
K-jetronic- K is for continuous, the system is mechanical with parts that control cold start
and idle that are electrical or electrical with vacuum assistance.
The amount of fuel is controlled in proportion to air flow to give the correct
air- fuel ratio. Air flow is measured by a metal plate in a cone shaped cylinder.
A plunger is connected to this plate. The plunger controls the pressure in the fuel
metering unit. The pressure is produced by the fuel pump operating at a specified
pressure particular to each vehicle. There is a differential pressure controlled by
the plunger. This differential pressure operates the injectors. The greater the air
the greater the differential pressure, the more fuel that is injected. The fuel is
continuously injected rather than with each intake opening.
K-jetronic with lambda- operation is the same as above with the addition of a lambda
(oxygen sensing). The lambda was added to further help the emissions of the
vehicle. By sensing the oxygen in the exhaust, the lambda will adjust the
co content.
NOTE: I have included a Theory of Operation to help in the understanding, operation
and troubleshooting of the CIS system.
4
Getting Started:
There are a few things that you should do before trouble shooting the fuel system.
You will need to ask a few questions to your self. By doing this you may be able to
find the problem and not have to test the system.
Ask the following questions ...
What is the problem? Cold start ...Hot start...Driveability...
When did the problem start? Overnight ..After driving ...Damp day...After fueling ...On startup
How was the car running before the problem started? Good ...Fair ...Poor...
What was done to the car at the last service? Oil change ...Tune up ...Engine overhaul…
Were there any other problems before the new problem started? Low battery ...Bad fuel pump
Correct starting procedure:
1973-1975 required the hand throttle to assist in starting. 76-83 did not.
By answering the above questions you may be able to narrow the possible problems to just a
few.
1. Make sure the Battery is in good condition.
2. Check the Connections to the battery. Clean the connections just in case.
3. Make sure the Ignition System is in good condition.1nspect plugs, check condition of
distributor, check the wiring, check the coil and check the timing. You need to be sure all
of these are in good condition before starting. You can check each of the above with out
the engine running. Do a static test on the timing if the engine is not running. Pull each
plug, clean if necessary, replace if needed.
4. Make sure the condition of the Engine is good.
5. Check the Starter.
6. Check the outside of the engine Rubber boots, Hoses, Electrical connections and Vacuum
Hoses.
7. Do a sniff test if the car has been sitting for a long period of time. Carefully sniff the fuel.
If the fuel smells like varnish, drain the fuel tank and fill with clean fuel.
8. Keep in mind that if the fuel is bad you may have some components that are covered with
this bad fuel. Examples would be the mixture control unit, fuel filter, cold start valve, fuel
accumulator, fuel pump, fuel check valve and fuel injectors. If you have bad fuel and there
is evidence of varnish, a brownish, sticky material, is indication that the car has been
sitting for a long period of time, it would be a good idea to inspect and clean all of the
above. I would suggest not disassembling the mixture control unit, buy a reconditioned
unit from a good parts supplier, you will save a lot of time and frustration.
9. Check the condition of the wiring. There should be no cuts, burns or stiffness in any of the
wires. Check the ground wires and the ground to the battery.
10. Check to see if the flow sensor plate moves freely. You will have to remove the air cleaner
to do this check. While you are there check to see if there is evidence of "backfire". See if
an anti backfire device has been installed. If it has not been installed, it is recommended
that you install one, see the photo in the photo section.
11. If all the above has been checked and the condition of the engine is found to be safe,
apply power and start a process of elimination.
12. Apply power to the car and try to start the engine.
If the engine does not start go to the Trouble Shooting Chart.
5
Trouble Shooting Chart:
Engine does not start/starts hard cold:
1. Sensor plate or plunger not moving freely:
Remove air filter and gently apply pressure to the sensor plate. If the plate does not
move, there may be an internal problem. Look for any possible cause for the binding
externally. If this fails, remove the fuel distributor and have it repaired or replaced by
a qualified repair shop.
2. Auxiliary air valve does not open:
Remove the hoses from the valve and verify that the valve is open. If not check that the
electrical connection is good and that there is voltage present with the ignition on.
3. Electric fuel pump not operating:
Check the fuel pump fuse and the pump relay, if both are good check voltage at the fuel
pump, if good replace fuel pump.
4. Thermo time switch defective:
Disconnect the connection to the cold start valve. Put a test light across the terminals.
Run the starter, the light should stay on for a few seconds, depending on the temperature
of the engine. If the light does not work, check for voltage on the yellow wire between the
starter and the Thermo switch. If there is voltage to the switch and the light does not
work, replace the Thermo time switch.
5. Cold control pressure out of tolerance:
Check the control pressure Regulator. Check the voltage at the connector to the
regulator - at least 11.5 volts. With power off and the connector off, check for continuity,
if none replace the regulator.
6. Injector leaking, opening pressure low:
With the engine not running pull the suspected injector and look for any leaks. If leaking
replace with it new injector.
7. Injected fuel quantities not equal:
Suspect that there is an injector problem. Pull each injector and test for quantity of fuel
injected into a measuring container. Run the engine for a short time for each injector.
Compare the amounts of fuel. Replace the injector that is not operating correctly.
8. Basic idle setting incorrect:
Check the speed and adjust as necessary.
9. Fuel Accumulator and/ or Fuel Pump Check Valve:
These keep pressure on the system.
6.1
Engine will not start Warm
1. Air flow sensor plate not adjusted correctly:
Remove the boot and the air filter and check the position of the plate as compared to the
barrel. The plate should be even to the bottom of the barrel, a tolerance of +/- .020 is
allowed. You can adjust the plate: 1973 ½ - 1975 by bending the clip and 1976- 1983 by
adjusting the screw with an allen screw driver. The screw driver is put m at the top of the
mixture control unit through a hole.
2. Fuel pressure is not correct:
Check fuel pressure at the fuel pump.
3. Cold Start valve leaking:
Check the cold start valve by removing the part from its location. Leave the fuel line
connected. Remove the connector, place the valve over a container and apply voltage to
on of the connectors and a ground to the other. Look for a coned shaped injection of fuel.
Turn off the power and wait a few seconds. Watch for leaks. If either of the above does
not work, replace the valve.
4. Vacuum Leaks:
Carefully inspect the complete engine for any cracked or worn hoses.
Look for connections that may be loose or have come loose.
5. Control Plunger in Fuel Distributor binding:
Check this by first depressurizing the fuel system. Do this by relieving the fuel pressure at
the warm up regulator. Remove the fuel filter and carefully move the plate up and down.
This movement should be free and with no binding. If you detect binding, replace the fuel
distributor with a rebuilt unit.
6. Fuel Accumulator and/or Fuel Pump Check Valve:
These hold pressure in the fuel system.
7. Fuel injector Clogged:
Pull the injectors and inspect for correct operation. Apply power to the fuel pump,
jump the wire terminal numbers 30 and 87a. Caution fuel will flow from the injectors
when the air flow plate is moved in an upward direction. Check for correct operation.
8. Control Plunger in the fuel distributor binding:
Remove the air cleaner and carefully move the plate up and down, do not force the plate.
If it binds investigate. If it is not simple to repair replace the unit.
9. Idle speed, Ignition Timing, and mixture out of tolerance:
Check and adjust all of the above.
10. Faulty Ignition System:
Check the ignition system. 1973-1977 check point gap .016, correct plugs see chart,
Condition of cap and rotor, 1978-1983 check for a distinctive hum in the CDI with ignition
on in engine compartment, (if no hum the CDI may be defective) CDI is the ignition
module located on the relay panel in the engine compartment left side.
6.2
Low Power:
1. Fuel Pressure Incorrect:
Check for pressure to be at least 66 PSI.
If too low, test the fuel pump and the warm up regulator.
2. O2 Sensor defective:
Replace as needed.
3. Fuel injector clogged:
Test the fuel injectors for equal quantities at a given time. Jump the fuel pump relay #30
and 87a. Run the pump with the injectors in a container. Look for problems.
4. Fuel distributor binding:
Check the plate for free movement. Remove the air cleaner and the air intake and gently
move the plate. It must move freely, if not look for the problem.
If it is not easy to repair replace the distributor.
5. Idle speed, Ignition timing or bad Ignition system:
Check the timing. Check the points 1973 - 1976 gap .016, 1977 - 1983 Check the CDI for
a distinctive hum with the ignition on. CDI is located in the engine compartment.
The CDI is the ignition module.
6. Full Throttle switch faulty or not adjusted correctly:
1980 -1 983 cars. This switch is located on the throttle body. It will at full throttle
disconnect the O2 sensor and allow open loop (a richer mixture) and turn off the air
condition during full throttle. The switch looks like a little black box.
Test the switch for continuity.
6.3
Poor Fuel Mileage:
1. Fuel Pressure incorrect:
Test fuel pressure. It should be at least 66 PSI.
2. Cold Start Valve Leaking:
Test cold start valve. Remove the valve and leave the fuel line connected.
Disconnect the electrical connection to the valve. Apply 12 Volts to one side of the valve
and a ground to the other side. Fuel will spray so do this over a container. Remove the
power and look for leaks. If there are and replace the valve.
3. Fuel Leaks:
Look and sniff for leaks. Repair as necessary.
4. O2 Sensor faulty:
Replace as necessary.
5. Idle Speed, Ignition timing and Idle Mixture CO out of Adjustment:
Make adjustments as necessary.
6. Control pressure regulator faulty:
Disconnect the electrical connection at the regulator and turn the switch on, check for
a voltage of at least 11.5 volts. Turn the switch off and test for continuity. If either of
these test bad, replace the control pressure regulator.
7. Fuel pump not working:
Check the fuse and the relay. Test for voltage at the pump.
If these test good replace the pump.
8. Warm Control pressure to high:
Check the wann up regulator. 1973 ½ check the connections to the regulator. If this
regulator is defective, you will have to replace the regulator with a later version.
Consult a Porsche parts house for the correct replacement. 1974 – ‘83 check the
connections at the regulator. Check for voltage at the connection and units with vacuum
connections check for leaks.
9. Fuel system leakage:
Suspect a leak if you smell raw fuel in the engine compartment.
Inspect all connections and any injector or fuel connection.
10. Injected fuel quantities unequal:
Test the amount of fuel delivered by each injector. Pull each injector and collect the fuel
as you test run the fuel pump. Compare the quantities. Replace the defective injector if
the quantity is not the same as the others.
11. Basic idle setting not correct:
Check the idle and adjust as necessary.
6.4
Idle Bad with Cold Engine
1. Leaks in air intake system:
Check all air intake and vacuum connections. Any old hoses must be replaced.
Be sure to check the intake boots around the intake runners. Check all hose clamps.
Replace any collapsed hoses.
2. Auxiliary Air Valve does not open:
Check the hose connections to the valve. If these check good remove the valve and
check for leaks by closing off one end and applying a small amount of suction to the
other end, if air can be drawn through the valve, with the other end capped off,
replace the valve.
3. Cold Start Valve leaking:
Remove the cold start valve, located in front of the intake. Leave the fuel line connected,
place the valve over a container, disconnect the electrical connection, apply 12 volts
to one of the connections, apply a ground to the other side, look for an even conical
spray pattern, turn the power off, wait a few seconds, there should be no leaks. If
the pattern is not correct or the valve leaks, replace the valve.
4. Cold control pressure not correct:
Check the warm up regulator. I would look for a pressure of at least 1.25 -1.50 bar
(18-22 PSI) at freezing temperatures. Be sure to check the pressure coming from the
mixture control unit.
If the pressure is not correct, do a complete check of the warm up regulator.
5. Injector Leaking:
The opening pressure could be to low, opening pressure should be around 2.5-3.6 bar
(36-52 PSI). Check all the injectors for evidence of leakage. Test for opening pressure.
When you reinstall the injectors be sure to replace the o-rings.
6. Injected Quantities low:
Compare the fuel quantities of each injector. Place each injector over a container and
record the amount of fuel each produces at a given amount of time. They should be equal.
7. Basic Idle incorrect:
Check and rest the idle per the specifications. It is best to set it when the engine is warm.
Check the co output, also.
8. Fuel Leaks:
Inspect all fuel connections.
9. Fuel injector Clogged:
Pull the injectors and inspect for correct operation. Apply power to the fuel pump,
jump the wire terminal numbers 30 and 87a. Caution fuel will flow from the injectors
when the air flow plate is moved in an upward direction. Check for correct operation.
10. Control Plunger in the fuel distributor binding:
Remove the air cleaner and carefully move the plate up and down, do not force the plate.
If it binds investigate. If it is not simple to repair replace the unit.
11. Idle speed, Ignition Timing, and mixture out of tolerance:
Check and adjust all of the above.
12. Faulty Ignition System:
Check the ignition system. 1973-1977 check point gap .016, correct plugs see chart,
Condition of cap and rotor, 1978-1983 check for a distinctive hum in the CDI with ignition
on in engine compartment, (if no hum the CDI may be defective) CDI is the ignition
module located on the relay panel in the engine compartment left side.
6.5
Misses and Hesitates under a load
1. Fuel pressure incorrect:
Test fuel pressure.
2. Fuel injector clogged:
Same as above #9
3. Control Plunger Binding:
Same as above #10
4. Incorrect ignition timing or faulty ignition system:
Same as above #12
5. Clogged Fuel Filter:
Check the fuel filter. Replace if necessary.
6. Faulty injector:
Test all injectors for quantity and leaks.
7. Vacuum leaks:
Inspect all hose connections and clamps. Replace all old and loose fitting hoses.
8. Fuel Pump not working:
Check for voltage at the pump. If no power check the fuse and the relay.
Replace if necessary.
If there is voltage at the pump and it is not running replace the pump.
9. Warm Control Pressure too high:
Check for at least 40 PSI with out vacuum on the warm up regulator and 46 PSI
with vacuum on the warm up regulator.
10. Warm Control Pressure to low:
Check for at least 40 PSI with out vacuum on the warm up regulator and 46 PSI
with vacuum on the warm up regulator.
Hesitation on Acceleration
1. Air flow sensor plate not positioned correctly:
Check the plate. Remove the air cleaner and air intake. Check for at least a .020 clearance
between the plate and the bottom of the barrow. 1973-1976 adjust the clip. 1977-1983
adjust with a screw driver.
2. Fuel pressure not correct:
Check for pressure to be at least 66 PSI.
3. Fuel injector clogged:
Test the fuel injectors for quantities at a given time.
Jump terminal 30 and 87a to run pump.
6.6
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The Porsche 924 Factory Service Manual is a comprehensive guide that provides detailed instructions and specifications for maintaining and repairing Porsche 924 models. Whether you are a professional mechanic or a Porsche enthusiast, this manual will be an invaluable resource for ensuring the proper care and performance of your vehicle.
This manual covers various models of the Porsche 924, including:
- Porsche 924 Base
- Porsche 924 Turbo
- Porsche 924 Carrera GT
- Porsche 924 S
- Porsche 924 Turbo S
- Porsche 924 Carrera GTS
Each section of the manual provides detailed explanations, diagrams, and step-by-step instructions for a wide range of maintenance procedures, including:
- Engine maintenance and repair
- Transmission and drivetrain maintenance
- Suspension and steering system maintenance
- Electrical system troubleshooting
- Brake system maintenance and repair
- Body and interior maintenance
With the Porsche 924 Factory Service Manual, you can confidently tackle any repair or maintenance task, knowing that you have accurate and reliable information at your fingertips. Keep your Porsche 924 running smoothly and efficiently with this essential manual.
