I posted this previously. There are always new members so I thought I'd repost it.
There are always questions posted about how to cure hard starting, hot
or cold. I've taken the time to summarize the information provided in
the workshop manual.
Soap box:
Electronic pulsed fuel injections systems are complex and are not a
topic for back-yard mechanics. I highly recommend that unless you have
a set of workshop manuals, testing tools and gauges and posses an
understanding of injection systems that you do not attempt to service
the systems.
Before laying blame: check for vacuum leaks and proper spark; check
plug wires, distributor cap, and spark plugs first. These are easily
serviceable items.
Troubleshooting:
If the spark system is up to snuff and you're not going to tear into the
system yourself, it is very important that you find a
mechanic/technicians that is familiar with the L or LH Jetronic
injection system, this isn't a skill that all or most
mechanics/technicians would generally have. Next, it is good if the
Jetronic literate mechanic/technician be familiar with 928s. Being
familiar with the plumbing and quirks of the 928 could lead to less
troubleshooting time and a lower repair bill.
L-Jetronic (US/Japan 1980 - 1984)
There are always questions about fuel injection related problems. The
following is a summary of the symptoms, causes and corrections from
section workshop manual page 24 - 21.
Step 1: The ignition, engine mechanical, battery charge must be fully
operational before testing the fuel system. This includes checking for
vacuum leaks!!!
Symptoms:
1. Engine will not start
2. Engine starts, but stops
3. Rough idle
4. Poor acceleration
5. Engine misfires in all load conditions
6. Excessive fuel consumption
7. Maximum power output not reached
8. CO level at idle speed too high
9. CO level at idle speed too low
Symptoms / Potential Cause / Corrective Action:
1,2 / AFC Relay (XIV) defective/check relay and power system
1 / Fuel pump not running / Check pump fuse, voltage at relay and fuel
pump
1 / Cold start valve will not open / Resistance about 4 ohms, check
ejection
1,2,6,8 / Cold start valve leaks / Check for leaks in pressure test
1 / Temperature time switch / check switching point
1,2,4 / Auxiliary air regulator will not open / Visual inspection: warm
engine - valve closed, cold engine - valve opened , electronics OK
1,2,4,6,7,8,9 / Intake air sensor defective / Check movement of sensor
plate, remove any dirt
1 / Pump relay defective / Check relay and power system
1,3,4,8 / Leak in intake system / Check intake pipes, bolted equipment
and all hose connections for leaks
1,3,6,7,9 / Fuel injectors defective / Test injectors
1,3, 8 / Fuel pressure too low or zero / Check pressure, filter, fuel
lines, pressure regulator
6,8 / Fuel pressure too high / Pressure regulator, intake pipe
connection, hose connection, fuel return line clogged or pinched,
pressure regulator defective
1,2,6,8 / Temperature sensor II in engine defective / measure resistance
3 / Throttle won't close / Service throttle valve, align accelerator
linkage, adjust throttle
7 / Throttle won't open fully / Adjust linkage and accelerator cable to
final stop
1,2,3,4,5,6,7,8,9 / Break in wiring harness and plugs / Correct break
3,4,7 / Throttle switch defective / check adjustment, check full
throttle and idle contacts
6, 8 / CO level setting too rich / Check idle speed and CO level
3, 9 / CO level setting too lean / check idle speed and CO level
8 / Oxygen sensor defective / replace sensor
1,2,3,4,5,6,7 / Electronic control unit defective / replace "brain
box"
LH- Jetronic: (all except US/Japan 1984 onwards, US/Japan 1985 onwards)
The following is a summary of the symptoms, causes from section workshop
manual page 24 - 111.
Symptoms:
1. Engine will not start
2. Engine starts, but stops
3. Rough idle
4. Poor acceleration
5. Engine misfires in all load conditions
6. Excessive fuel consumption
7. Maximum power output not reached
8. Engine hesitation
Symptoms / Potential Cause:
1,2,4,5,7,8 / Ground and plug connections
1,8 / Power supply for control unit and fuel pump
3,4,5,6,7,8 / Air flow sensor
1,2,3,4,6,7,8 / Temperature sensor II
4,5,6,7 / Throttle switch
1,2,3,4,6,7,8 / Fuel injectors and injection timing
2,8 / Auxiliary air regulator
3,4,6,8 / CO and idle speed adjustment
2,3,4,7,8 / Leaks in intake manifold
1,2,3,4,6,7,8 / Fuel
5,8 / Alternator - Regulator
Enjoy,
Rich
'93 GTS
'83S
Charter Member 928 OC
================================
Dan,
This isn't much, but I tried to identify the things that could keep the car
from starting and or running in the Fuel Injection system.
This assumes that the fuel pressure is OK.
This is tested mostly from the passenger footwell.
With everything connected get your volt meter and find a good ground point.
On my car the two lower bolts that hold in the bottom of the fuse panel
board, only the right hand bolt has a good ground. Your car may be
different.
These tests are for voltage between the selected pin and chassis ground.
Connector W is at the lower righthand of the fuse and relay panel.
1. Connector W14 to ground - With the ignition on this should have 12v.
2. Connector W23 to ground - With the ignition on this should have 12v.
3. Connector W21 to ground - With the engine cranking, I think, this
should
be less than 1 volt. This may go to less than 1 volt with just the
ignition
on.
Switch from measuring volts to Ohms.
4. Remove the LH connector - measure Ohms on the wiring connector.
5. Pin 2 to ground - This is temp sensor II input.
Should be 4K Ohms
to 7K Ohms at about 30 degrees.
Should be 400 Ohms
to 700 Ohms at about 100 degrees.
6. Pin 3 to ground - This is the Throttle Position Sensor,
Idle position.
Should read about 0 Ohms.
7. Pin 5 to ground - This is a chassis ground connection. Should be
.0 to
.4 Ohms.
8. Pin 11 to ground - This is a chassis ground connection. Should be
.0 to
.4 Ohms.
9. Pin 12 to ground - This is the Throttle Position Sensor,
WOT
position. Should read about infinate Ohms.
10. Stay on pin 12 to ground and press the accelerator all the way to the
floor board. Should read about 0 Ohms when the gas pedal is floored.
This
probably would not keep the engine from starting though.
11. Pin 25 to ground - This is a chassis ground connection. Should be .0
to
.4 Ohms.
12. Pin 6 to pin 7 - Should be 3 - 4 Ohms. This is the AMS hot wire.
13. Pin 6 to pin 14 - Should be in the range of 0 Ohms to 1000 Ohms. This
is the AMS mixture adjustment screw.
These are all of the things that should keep your car from running, at the
connector. If these are all OK, go to the engine compartment.
You'll need to get access to one of the rear fuel injectors. I had to
remove the Air filter housing. I did the drivers side rear injector.
14. Remove the Fuel injector connector and check the Ohms between the two
pins on the connector. It should be about 2 Ohms. ie. Each injector
should
be about 15.3 Ohms, devided by 7 = 2.~ Ohms.
This is where the fault was on my car. Mine was at .3 Ohms.
Hope this helps. Let me know how the tests go and I can probably help you
further.
Ken Postma 86.5 928S
==========
Basically, the LH has these inputs/outputs:
1 input from O2 sensor signal
1 input from AMF signal
1 input from coolant temp sensor (temp II sensor)
1 input from intake air temp sensor (on top of the manifold)
2 inputs from throttle switch (idle and WOT) for 2.4.1
1 input from A/C system telling it the compressor has been turned on
1 input from EZK ignition (similar to tachometer signal)
--
*1* output to batch-fire injectors
2 or 3 (in the 928's case 3) outputs to idle stabilizer valve
1 output to the charcoal canister purge valve
Dave