Engine
L and LH Jetronic Diagnostics
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 backyard 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