I hope you're well. I have a question for you regarding your diagnostic software and a no start condition on my '93 (early) 928 GTS.

I have almost 180,000 miles on the car. Earlier this summer, I couldn't get the car to start. It cranks fine but won't fire. It has plenty of gas. I sprayed some starting fluid into the intake and it still wouldn't fire. I'm finally getting around to working on it and was wondering if the diagnostic software can be used to troubleshoot the problem. It seems to me that the diagnostic software is designed for use when the car is already running, and of course, it won't start

Paul.
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First of all: a 928 engine can get flooded by fuel when for some reason it did not start. It happens sometimes and it takes a while for fuel to evaporate before it can start again. It can help disconnecting the LH cable, charge the battery and make sure it stays full, and start the engine a few times while pressing the gas pedal to the floor. Since the LH cannot inject anymore the airflow will help getting rid of fuel mixture. Talking the plugs out will even help more but is more work.

Next: verify that relays work. Test the LH, EZK, and Fuel pump relay in the horn socket and use the horn relay (hardly ever used) as test in the LH EZK and Pump socket.

Unplug one ignition cable and undo the sparkplug (or use a spare one). Hold the plug against the engine and have someone try to start. Do you have sparks? If so, the TDC sensor works and the EZK works.

Next: while having someone start: put a long screwdriver on every injector housing and the other side against your ear. You should hear a loud click while starting. If so, the LH and IMR work.

Next, when starting, do you hear the fuel pump run? It should be humming while you try to start. If so, the LH is active and the LH relay and pump relay work.


Let me know how we can help…
Regards
928-ecu-repair
Paul & Theo
Theo Jenniskens
1992 928GTS midnight blue
http://928gts.jenniskens.eu
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Theo, you're a genius! After reconnecting the UDT999 and running through everything I could do with the car off and finding no faults, I disconnected the LH computer and tried to stay out with the gas pedal floored. The car immediately started and ran for a few moments! After it died, I reconnected the LH and now it's running and starting fine again. I haven't driven it all summer!

Now the question is, why would it flood and not start? I checked my fuel pressure and delivery when I was troubleshooting. I have 3.75 bar pressure when the fuel pump relay is bridged. After several hours, it had dropped to 3.5. Would that indicate an injector leak?

Thank you again! I would never have thought to disconnect the LH computer and try and start it.

Paul
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Hello Paul,
Thanks for the nice feedback and super that your 928 runs again.
The 928 does this sometimes. I think it is because of a failure to start while injecting quite a bit of fuel. The LH ecu adds fuel when the engine is cold. A bad temp2 sensor, leaking pressure dampers and regulator, or leaking injectors could even make things worse. However… this flooding happens only when something went wrong in the first place. A simple “a few times: no start and try again” can trigger this. Sparkplugs get wet and the engine won’t start. I know these things from experience.

A leaking injector can add to the problem, but if your 928 fuel pressure drops just 0.25 in a few hours I’d say it is ok. No issue, normal behaviour. If the injectors or dampers would leak your pressure would drop a lot faster.

Enjoy your 928 !!!
Regards Theo