Hi List I need some help. The other day after some spirited driving I
return Home all is ok. I rev the engine because I have a slight vibration
and I'm trying to isolate it. One other thing I had very little gas. While
during my high revving thing A large black patch of smoke comes out of the
exhaust and the car dies the engine made no weird noise it just stops. I
try to restart no go. I let it cool down and try again no go. So now I'm
thinking bad fuel. So I disconnect the fuel line and blow them out with
compressed air. I try again no start. I blow out the lines again. I have
fuel and pressure for sure. Next thing I check is for spark. I do have
spark. Then I then take off all the plugs and clean them. One thing now
all the intake tubes have a oil on them and a lot in the 2 side thingy
where it 32v Porsche blah blah blah. Clean those out reassemble and try
to start no go. I have tried Starting fluid in the throat no start. I
think I hear the injector ticking when it trying to crank. So now I'm
thinking - it jumped timing, it's a new belt and recently re tensioned.
OUCH!! Well how can I tell if this it the issue and if, well you know the story, I have bent valves and big $$ in front of me. Any Help is appreciated Roy
Back to basics: Fire, Fuel, Air , Compression.
Your '86.5 has basically two different ignition systems. You have spark - Where? Do you have a regular strong spark at all eight plugs? Safest way to check is with an inductive pick-up timing light. The 928 system is powerful enough to hurt you or the system if you try to check by pulling plug wires. If you had no spark, the most common answer is the EZK relay.
You need fuel flow, pressure and injection. First check is usually to hear the fuel pump buzzing as the starter operates - if no buzz, the most likely problems are fuel pump relay, bad fuse connection, bad pump connection and bad pump, in that order. Plugged lines or filter is very rare. Injector check is to actually listen to the injectors as the starter operates. A mechanic's stethoscope is the best way, but a long rod will work. If no clicking, the most common problem is the LH relay. Black smoke is an indication of too much fuel or not enough fire. Each of the fuel pressure regulators and dampeners have a vacuum line attached. Pull each vacuum line and check for any trace of fuel in the line. Replace any leaking unit.
Not commonly a problem on the 928, but watch for shop rags and birds sucked into the intake.
Timing belt failure isn't common, but it does happen. If you turn the engine so that the crank is on 0 deg (TDC), remove the air intake tubes, and look into the two little spouts on the top of the belt covers, you should be able to see the cam sprocket timing marks - IF ... IF you know what you are looking for. The cam sprocket marks are tiny notches in the BACK edge of the sprockets, that line up with the marks cast into the cover backing plates. IF you are at TDC firing instead of exhaust. If you see no marks, turn the engine one turn back to TDC and look again. You can also look thru the ventilation spouts at the belt as someone operates the starter. The belt should look perfect, and should move smoothly in time with the crankshaft.
Ok, first of all, my '88 auto always starts when I hit the key, 1-2 seconds
and it's running, maybe 3 seconds on a very very bad day. So, just finished
torque tube rebuild and t-belt replacement, turn the key and it immediately
fires, 2 seconds later stops, won't fire again. Pump runs when it should, all
wires ok, but now with the ignition in the "on" position, it sounds like a
miniature jackhammer from somewhere in the middle of the motor, can't tell
exactly where, stethoscope didn't help. Never heard that noise from a 928
Gas tank almost full, battery fully charged, etc.
Since you said you just did a timing belt, it raises the radar. The symptom
you are getting matches exactly the symptom I was getting from an 85 that jumped
the belt. I had just bought the car knowing the mechanic had identified the
problem as a jumped belt. As a lark after the car was tow to my place I tried to
start it. Immediately it started and ran two or three seconds and then shut
down. All the cranking in the world and no start.
Since it was a few days before I could get into the motor I disconnected the battery. When I got back to the job I got the same symptom of an immediate
Check the timing on your belt!
Dan the Pod Guy
I have a black on black, 1987 5spd, w/50K miles. I am pretty useless as far as fixing anything, hence the lurking! I find myself having a few problems w/the shark and hope someone can lend some insight. Car has new battery, plugs, wires, coils, filters (everything from 928 Specialists) and has been running fine for the last year. I went through a period of not driving it (8 weeks) and the battery died on me, even though I had the Porsche battery maintainer installed, I did not use it (afraid it might cause a problem to the computer).
>>Neither the maintainer nor a properly-operating battery charger should damage the electronics in a 928.
After the car died, I plugged in the maintainer. I tried starting it today, after about 4 weeks on the maintainer, the car seems to turn over strong, but will not start. Seems like plenty of juice from the battery, no smoke, no clicking noises. I tried w/no accelerator and then holding the pedal down for >about 10 seconds. Starter and alternator are original.
>>"Relay, relay, relay." - J. Bailey
First, kneel by the rear bumper and listen carefully for the buzz of the fuel pump as someone operates the starter. If there is no buzz as the starter operates, swap relays XX (fuel pump) and XII (horn) and try again.
If the fuel pump buzzes, open the hood, turn the ignition on (don't try to start the engine yet), and listen very carefully for clicking from the injectors. If the injectors are clicking, the LH (injection) ECU has died.
If there is no clicking, have someone operate the starter and see if you can hear clicking from the injectors. If the injectors don't click, swap relays XXV (injection) and XII (horn) and try again..
If you have both the fuel pump buzz and injector click (only while the starter is operating!), swap relays XVI (ignition) and XII (horn) and try again. Don't worry that Relay XVI looks different - it is functionally identical.
928 Model year 1987 – 1988 System No Start Diagnostics (1989 and later 928
systems are similar):
Diagnostics should be only be performed by a trained technician. Always check for proper relay functionality and power/ground connections before undertaking further diagnostic testing.
a. Testing the engine RPM sensor. The EZK spark control is the system master, if engine rotation signals are not provided to the EZK, spark will not be generated and EZK will not provide a turn-on signal to the LH Jetronic fuel injection system. The RPM sensor input to the EZK is from an inductive RPM sensor. Inductive RPM sensors generate voltage so a VOM can be used for testing the sensor. EZK pins 23 and 6 are connected to the RPM sensor; pin 6 is ground and is connected to master-ground pin 18. EZK pin 24 is the shielding of the sensor cable and is connected internally to pin 18.
b. The Hall Effect engine position sensor can be tested with an LED tester. The EZK provides the power supply for the Hall Sensor at pin number 5 (12V). The EZK provides a 5V level at pin number 22, which the Hall sensor can pull down to ground. Pin EZK pin 22 is the "hot" signal cable and therefore is shielded. The cable shielding is connected to EZK pin 4, and pin 4 is connected internally to master-ground EZK pin 18.
c. The EZK spark module provides the signal to turn on the LH fuel injection module; it is the circuit from EZK pin 13 to LH control Pin 1. Check for continuity, if the wire is broken or the connection isn't clean, the car will not start.
d. The circuit from LH Pin 20 goes to the Fuel Pump Relay XX pin 85, check for continuity between these two points.
e. From the Fuel Pump Relay XX pin 87 the circuit passes through fuse 42 then to the fuel pump motor. Pull the fuse, check the fuse, and clean the connectors. Check the continuity of this path. Bridge Fuel Pump Relay XX socket points 30 and 87, the fuel pump should run.
f. There should be 12V (nominal battery voltage) at the fuel pump and LH relay pins 30 at all times. This same circuit connects to LH connector Pin 4, check for 12V there too.
g. The LH relay XXV pin 85 connects to LH connector pin 21, check for continuity between these two points.
h. The LH connector pin 18 connects to all the fuel injectors. The LH functions as the switch from the fuel injector to ground. With the LH relay jumpered between pins 30 and 87, there should be 12 V at pin 18. [Model Year 1989 and newer 928s have a spark monitoring system, consult the wiring schematics and workshop manuals.]
i. Power and Ground connections are key points to inspect and clean. The LH is grounded via Pin 17 to chassis ground point VIII. Use an Ohm meter to measure the resistance between LH connector Pin 17 and a chassis ground point. It should read as close to zero as possible. If it reads a high resistance, a corroded ground connection at MP VII or cut in the wire could be the problem.
j. If all of these items check out OK, and the fuel pump is functioning, then potential problems could be:
- The system fuel pressure is too low; fuel filter or pipes are restricted, fuel injectors are not functioning correctly
- The LH Jetronic fuel injection module is not functioning correctly and requires a rebuild.